# Atmospheric Chemistry / Climate Modeling

2020
Fu, XW, SL Xiang, Y Liu, J Yu, DL Mauzerall, and S Tao. “High-resolution simulation of local traffic-related NOx dispersion and distribution in a complex urban terrain.” Environmental Pollution 263 (2020).Abstract
Urban air pollution features large spatial and temporal variations due to the high heterogeneity in emissions and ventilation conditions, which render the pollutant distributions in complex urban terrains difficult to measure. Current urban air pollution models are not able to simulate pollutant dispersion and distribution at a low computational cost and high resolution. To address this limitation, we have developed the urban terrain air pollution (UTAP) dispersion model to investigate, at a spatial resolution of 5 m and a temporal resolution of 1 h, the distribution of the local traffic-related NOx concentration at the pedestrian level in a 1 × 1 km2 area in Baoding, Hebei, China. The UTAP model was shown to be capable of capturing the local pollution variations in a complex urban terrain at a low computational cost. We found that the local traffic-related NOx concentration along or near major roads (10–200 μg m−3) was 1–2 orders of magnitude higher than that in places far from roads (0.1–10 μg m−3). Considering the background pollution, the NO and NO2 concentrations exhibited similar patterns with higher concentrations in street canyons and lower concentrations away from streets, while the O3 concentration exhibited the opposite behavior. Sixty percent of the NOx concentration likely stemmed from local traffic when the background pollution level was low. Both the background wind speed and direction substantially impacted the overall pollution level and concentration variations, with a low wind speed and direction perpendicular to the axes of most streets identified as unfavorable pollutant dispersion conditions. Our results revealed a large variability in the local traffic-related air pollutant concentration at the pedestrian level in the complex urban terrain, indicating that high-resolution computationally efficient models such as the UTAP model are required to accurately estimate the pollutant exposure of urban residents.
2019
Qin, Yue, Yuanyuan Fang, Xiaoyuan Li, Vaishali Naik, Larry W. Horowitz, Junfeng Liu, Noah Scovronick, and Denise L. Mauzerall+. “Source attribution of black carbon affecting regional air quality, premature mortality and glacial deposition in 2000.”  Atmospheric Environment 206 (2019): 144-155.Abstract
Black carbon (BC) mitigation can reduce adverse environmental impacts on climate, air quality, human health, and water resource availability. To facilitate the identification of mitigation priorities, we use a state-of-thescience global chemistry-climate coupled model (AM3), with additional tagged BC tracers representing regional (East Asia, South Asia, Europe and North America) and sectoral (land transport, residential, industry) anthropogenic BC emissions to identify sources with the largest impacts on air quality, human health and glacial deposition. We find that within each tagged region, domestic emissions dominate BC surface concentrations and associated premature mortality (generally over 90%), as well as BC deposition on glaciers (∼40–95% across glaciers). BC emissions occurring within each tagged source region contribute roughly 1–2 orders of magnitude more to their domestic BC concentrations, premature mortality, and BC deposition on regional glaciers than that caused by the same quantity of BC emitted from foreign regions. At the sectoral level, the South Asian residential sector contributes ∼60% of BC associated premature mortality in South Asia and ∼40–60% of total BC deposited on southern Tibetan glaciers. Our findings imply that BC mitigation within a source region, particularly from East and South Asian residential sectors, will bring the largest reductions in BC associated air pollution, premature mortality, and glacial deposition.
2017
Guo, Yixin, Junfeng Liu, Denise L. Mauzerall, Xiaoyuan Li, Larry W. Horowitz, Wei Tao, and Shu Tao. “Long-Lived species enhance summertime attribution of North American ozone to upwind sources.” Environmental Science & Technology 51, no. 9 (2017): 5017-5025.Abstract
Ground-level ozone (O3), harmful to most living things, is produced from both domestic and foreign emissions of anthropogenic precursors. Previous estimates of the linkage from distant sources rely on the sensitivity approach (i.e., modeling the change of ozone concentrations that result from modifying precursor emissions) as well as the tagging approach (i.e., tracking ozone produced from specific O3 precursors emitted from one region). Here, for the first time, we tag all O3 precursors (i.e., nitrogen oxides (NOx), carbon monoxide (CO), and volatile organic compounds (VOCs)) from East Asia and explicitly track their physicochemical evolution without perturbing the nonlinear O3 chemistry. We show that, even in summer, when intercontinental influence on ozone has typically been found to be weakest, nearly 3 parts per billion by volume (ppbv) seasonal average surface O3 over North America can be attributed to East Asian anthropogenic emissions, compared with 0.7 ppbv using the sensitivity approach and 0.5 ppbv by tagging reactive nitrogen oxides. Considering the acute effects of O3 exposure, approximately 670 cardiovascular and 300 respiratory premature mortalities within North America could be attributed to East Asia. CO and longer-lived VOCs, largely overlooked in previous studies, extend the influence of regional ozone precursors emissions and, thus, greatly enhance O3 attribution to source region.
2016
Westervelt, D.M., L. W. Horowitz, V. Naik, APK Tai, AM Fiore, and DL Mauzerall+. “Quantifying PM2.5-meteorology sensitivities in a global climate model.” Atmospheric Environment 142 (2016): 43-56. Publisher's VersionAbstract
Climate change can influence fine particulate matter concentrations (PM2.5) through changes in air pollution meteorology. Knowledge of the extent to which climate change can exacerbate or alleviate air pollution in the future is needed for robust climate and air pollution policy decision-making. To examine the influence of climate on PM2.5, we use the Geophysical Fluid Dynamics Laboratory Coupled Model version 3 (GFDL CM3), a fully-coupled chemistry-climate model, combined with future emissions and concentrations provided by the four Representative Concentration Pathways (RCPs). For each of the RCPs, we conduct future simulations in which emissions of aerosols and their precursors are held at 2005 levels while other climate forcing agents evolve in time, such that only climate (and thus meteorology) can influence PM2.5 surface concentrations. We find a small increase in global, annual mean PM2.5 of about 0.21 μg m−3 (5%) for RCP8.5, a scenario with maximum warming. Changes in global mean PM2.5 are at a maximum in the fall and are mainly controlled by sulfate followed by organic aerosol with minimal influence of black carbon. RCP2.6 is the only scenario that projects a decrease in global PM2.5 with future climate changes, albeit only by −0.06 μg m−3 (1.5%) by the end of the 21st century. Regional and local changes in PM2.5 are larger, reaching upwards of 2 μg m−3 for polluted (eastern China) and dusty (western Africa) locations on an annually averaged basis in RCP8.5. Using multiple linear regression, we find that future PM2.5 concentrations are most sensitive to local temperature, followed by surface wind and precipitation. PM2.5 concentrations are robustly positively associated with temperature, while negatively related with precipitation and wind speed. Present-day (2006–2015) modeled sensitivities of PM2.5 to meteorological variables are evaluated against observations and found to agree reasonably well with observed sensitivities (within 10–50% over the eastern United States for several variables), although the modeled PM2.5 is less sensitive to precipitation than in the observations due to weaker convective scavenging. We conclude that the hypothesized “climate penalty” of future increases in PM2.5 is relatively minor on a global scale compared to the influence of emissions on PM2.5concentrations.
2015
Westervelt, DM, L. W. Horowitz, V. Naik, and DL Mauzerall+. “Radiative forcing and climate response to projected 21st century aerosol decreases.” Atmos. Chem. Phys. 15 (2015): 12681-12703.Abstract
2014
Shen, Z, J Liu, L. W. Horowitz, D. K. Henze, S. Fan, Levy II H, DL Mauzerall, J-T Lin, and S Tao. “Analysis of Transpacific Transport of Black Carbon during HIPPO-3: Implications for Black Carbon Aging.” Atmos. Chem. Phys. 14 (2014): 6315-6327.Abstract
Long-range transport of black carbon (BC) is a growing concern as a result of the efficiency of BC in warming the climate and its adverse impact on human health. We study transpacific transport of BC during HIPPO-3 using a combination of inverse modeling and sensitivity analysis. We use the GEOS-Chem chemical transport model and its adjoint to constrain Asian BC emissions and estimate the source of BC over the North Pacific. We find that different sources of BC dominate the transport to the North Pacific during the southbound (29 March 2010) and northbound (13 April 2010) measurements in HIPPO-3. While biomass burning in Southeast Asia (SE) contributes about 60 % of BC in March, more than 90 % of BC comes from fossil fuel and biofuel combustion in East Asia (EA) during the April mission. GEOS-Chem simulations generally resolve the spatial and temporal variation of BC concentrations over the North Pacific, but are unable to reproduce the low and high tails of the observed BC distribution. We find that the optimized BC emissions derived from inverse modeling fail to improve model simulations significantly. This failure indicates that uncertainties in BC removal as well as transport, rather than in emissions, account for the major biases in GEOS-Chem simulations of BC over the North Pacific. The aging process, transforming BC from hydrophobic into hydrophilic form, is one of the key factors controlling wet scavenging and remote concentrations of BC. Sensitivity tests on BC aging (ignoring uncertainties of other factors controlling BC long range transport) suggest that in order to fit HIPPO-3 observations, the aging timescale of anthropogenic BC from EA may be several hours (faster than assumed in most global models), while the aging process of biomass burning BC from SE may occur much slower, with a timescale of a few days. To evaluate the effects of BC aging and wet deposition on transpacific transport of BC, we develop an idealized model of BC transport. We find that the mid-latitude air masses sampled during HIPPO-3 may have experienced a series of precipitation events, particularly near the EA and SE source region. Transpacific transport of BC is sensitive to BC aging when the aging rate is fast; this sensitivity peaks when the aging timescale is in the range of 1–1.5 d. Our findings indicate that BC aging close to the source must be simulated accurately at a process level in order to simulate better the global abundance and climate forcing of BC.
Li, Xiaoyuan, Junfeng Liu, Denise L. Mauzerall+, Louisa K. Emmons, Stacy Walters, Larry W. Horowitz, and Shu Tao. “Effects of Trans-Eurasian Transport of Air Pollutants on Surface Ozone Concentrations over Western China.” Journal of Geophysical Research - Atmosphere (2014). Publisher's VersionAbstract
Due to a lack of industrialization in Western China, surface air there was, until recently, believed to be relatively unpolluted. However, recent measurements and modeling studies have found high levels of ozone (O3) there. Based on the state‐of‐the‐science global chemical transport model MOZART‐4, we identify the origin, pathway, and mechanism of trans‐Eurasian transport of air pollutants to Western China in 2000. MOZART‐4 generally simulates well the observed surface O3 over inland areas of China. Simulations find surface ozone concentrations over Western China on average to be about 10 ppbv higher than Eastern China. Using sensitivity studies, we find that anthropogenic emissions from all Eurasian regions except China contribute 10–15 ppbv surface O3 over Western China, superimposed upon a 35–40 ppbv natural background. Transport from European anthropogenic sources to Northwestern China results in 2–6 ppbv O3 enhancements in spring and summer. Indian anthropogenic sources strongly influence O3 over the Tibetan Plateau during the summer monsoon. Transport of O3originating from emissions in the Middle East occasionally reach Western China and increase surface ozone there by about 1–4 ppbv. These influences are of similar magnitude as trans‐Pacific and transatlantic transport of O3 and its precursors, indicating the significance of trans‐Eurasian ozone transport in hemispheric transport of air pollution. Our study further indicates that mitigation of anthropogenic emissions from Europe, the Indian subcontinent, and the Middle East could benefit public health and agricultural productivity in Western China.
2013
Fang, Yuanyuan, Denise L. Mauzerall+, Junfeng Liu, Arlene M. Fiore, and Larry W. Horowitz. “Impacts of 21st century climate change on global air pollution-related premature mortality.” Climatic Change 121 (2013): 239-253.Abstract
Climate change modulates surface concentrations of fine particulate matter (PM2.5) and ozone (O3), indirectly affecting premature mortality attributed to air pollution. We estimate the change in global premature mortality and years of life lost (YLL) associated with changes in surface O3 and PM2.5 over the 21st century as a result of climate change. We use a global coupled chemistry-climate model to simulate current and future climate and the effect of changing climate on air quality. Epidemiological concentration-response relationships are applied to estimate resulting changes in premature mortality and YLL. The effect of climate change on air quality is isolated by holding emissions of air pollutants constant while allowing climate to evolve over the 21st century according to a moderate projection of greenhouse gas emissions (A1B scenario). Resulting changes in 21st century climate alone lead to an increase in simulated PM2.5 concentrations globally, and to higher (lower) O3 concentrations over populated (remote) regions. Global annual premature mortality associated with chronic exposure to PM2.5 increases by approximately 100 thousand deaths (95 % confidence interval, CI, of 66–130 thousand) with corresponding YLL increasing by nearly 900 thousand (95 % CI, 576–1,128 thousand) years. The annual premature mortality due to respiratory disease associated with chronic O3 exposure increases by +6,300 deaths (95 % CI, 1,600–10,400). This climate penalty indicates that stronger emission controls will be needed in the future to meet current air quality standards and to avoid higher health risks associated with climate change induced worsening of air quality over populated regions.
Fang, Yuanyuan, Vaishali Naik, Larry W. Horowitz, and Denise L. Mauzerall+. “Air pollution and associated human mortality: The role of air pollutant emissions, climate change and methane concentration increases from the preindustrial period to the present.” Atmospheric Chemistry Physics (2013).Abstract
Increases in surface ozone (O3) and fine particulate matter (≤ 2.5 µm aerodynamic diameter, PM2.5) are associated with excess premature human mortalities. We estimate changes in surface O3 and PM2.5 from pre-industrial (1860) to present (2000) and the global present-day (2000) premature human mortalities associated with these changes. We extend previous work to differentiate the contribution of changes in three factors: emissions of short-lived air pollutants, climate change, and increased methane (CH4) concentrations, to air pollution levels and associated premature mortalities. We use a coupled chemistry-climate model in conjunction with global population distributions in 2000 to estimate exposure attributable to concentration changes since 1860 from each factor. Attributable mortalities are estimated using health impact functions of long-term relative risk estimates for O3 and PM2.5 from the epidemiology literature. We find global mean surface PM2.5 and health-relevant O3 (defined as the maximum 6-month mean of 1-h daily maximum O3 in a year) have increased by 8 ± 0.16 µg m−3 and 30 ± 0.16 ppbv (results reported as annual average ±standard deviation of 10-yr model simulations), respectively, over this industrial period as a result of combined changes in emissions of air pollutants (EMIS), climate (CLIM) and CH4 concentrations (TCH4). EMIS, CLIM and TCH4 cause global population-weighted average PM2.5 (O3) to change by +7.5 ± 0.19 µg m−3 (+25 ± 0.30 ppbv), +0.4 ± 0.17 µg m−3 (+0.5 ± 0.28 ppbv), and 0.04 ± 0.24 µg m−3 (+4.3 ± 0.33 ppbv), respectively. Total global changes in PM2.5 are associated with 1.5 (95 % confidence interval, CI, 1.2–1.8) million cardiopulmonary mortalities and 95 (95 % CI, 44–144) thousand lung cancer mortalities annually and changes in O3 are associated with 375 (95 % CI, 129–592) thousand respiratory mortalities annually. Most air pollution mortality is driven by changes in emissions of short-lived air pollutants and their precursors (95 % and 85 % of mortalities from PM2.5 and O3 respectively). However, changing climate and increasing CH4 concentrations also contribute to premature mortality associated with air pollution globally (by up to 5 % and 15 %, respectively). In some regions, the contribution of climate change and increased CH4 together are responsible for more than 20 % of the respiratory mortality associated with O3 exposure. We find the interaction between climate change and atmospheric chemistry has influenced atmospheric composition and human mortality associated with industrial air pollution. Our study highlights the benefits to air quality and human health of CH4 mitigation as a component of future air pollution control policy.
Avnery, Shiri, Denise L. Mauzeral+l, and Arlene M. Fiore. “Increasing global agricultural production by reducing ozone damages via methane emission controls and ozoneresistant cultivar selection.” Global Change Biology 19 (2013): 1285-1299.Abstract
Meeting the projected 50% increase in global grain demand by 2030 without further environmental degradation poses a major challenge for agricultural production. Because surface ozone (O3) has a significant negative impact on crop yields, one way to increase future production is to reduce O3-induced agricultural losses. We present two strategies whereby O3 damage to crops may be reduced. We first examine the potential benefits of an O3 mitigation strategy motivated by climate change goals: gradual emission reductions of methane (CH4), an important greenhouse gas and tropospheric O3 precursor that has not yet been targeted for O3 pollution abatement. Our second strategy focuses on adapting crops to O3 exposure by selecting cultivars with demonstrated O3 resistance. We find that the CH4 reductions considered would increase global production of soybean, maize, and wheat by 23–102 Mt in 2030 – the equivalent of a ~2–8% increase in year 2000 production worth $3.5–15 billion worldwide (USD2000), increasing the cost effectiveness of this CH4 mitigation policy. Choosing crop varieties with O3 resistance (relative to median-sensitivity cultivars) could improve global agricultural production in 2030 by over 140 Mt, the equivalent of a 12% increase in 2000 production worth ~$22 billion. Benefits are dominated by improvements for wheat in South Asia, where O3-induced crop losses would otherwise be severe. Combining the two strategies generates benefits that are less than fully additive, given the nature of O3 effects on crops. Our results demonstrate the significant potential to sustainably improve global agricultural production by decreasing O3-induced reductions in crop yields.
2011
Saikawa, E, J Kurokawa, M Takigawa, J Borken-Kleefeld, DL Mauzerall, L. W. Horowitz, and T Ohara. “The impact of China’s vehicle emissions on regional air quality in 2000 and 2020: a scenario analysis.” Atmospheric Chemistry and Physics 11 (2011): 9465-9484.Abstract
The number of vehicles in China has been increasing rapidly. We evaluate the impact of current and possible future vehicle emissions from China on Asian air quality. We modify the Regional Emission Inventory in Asia (REAS) for China’s road transport sector in 2000 using updated Chinese data for the number of vehicles, annual mileage, and emission factors. We develop two scenarios for 2020: a scenario where emission factors remain the same as they were in 2000 (No-Policy, NoPol), and a scenario where Euro 3 vehicle emission standards are applied to all vehicles (except motorcycles and rural vehicles). The Euro 3 scenario is an approximation of what may be the case in 2020 as, starting in 2008, all new vehicles in China (except motorcycles) were required to meet the Euro 3 emission standards. Using the Weather Research and Forecasting model coupled with Chemistry (WRF/Chem), we examine the regional air quality response to China’s vehicle emissions in 2000 and in 2020 for the NoPol and Euro 3 scenarios. We evaluate the 2000 model results with observations in Japan, China, Korea, and Russia. Under NoPol in 2020, emissions of carbon monoxide (CO), nitrogen oxides (NOx), non-methane volatile organic compounds (NMVOCs), black carbon (BC), and organic carbon (OC) from China’s vehicles more than double compared to the 2000 baseline. If all vehicles meet the Euro 3 regulations in 2020, however, these emissions are reduced by more than 50 % relative to NoPol. The implementation of stringent vehicle emission standards leads to a large, simultaneous reduction of the surface ozone (O3) mixing ratios and particulate matter (PM2.5) concentrations. In the Euro 3 scenario, surface O3 is reduced by more than 10 ppbv and surface PM2.5 is reduced by more than 10 µg m−3 relative to NoPol in Northeast China in all seasons. In spring, surface O3 mixing ratios and PM2.5 concentrations in neighboring countries are also reduced by more than 3 ppbv and 1 µg m−3 , respectively. We find that effective regulation of China’s road transport sector will be of significant benefit for air quality both within China and across East Asia as well.
Kopacz, M, DL Mauzerall+, J Wang, EM Leibensperger, DK Henze, and K Singh. “Origin and radiative forcing of black carbon transported to the Himalayas and Tibetan Plateau.” Atmos. Chem. Phys. 11 (2011): 2837-2852.Abstract
The remote and high elevation regions of central Asia are influenced by black carbon (BC) emissions from a variety of locations. BC deposition contributes to melting of glaciers and questions exist, of both scientific and policy interest, as to the origin of the BC reaching the glaciers. We use the adjoint of the GEOS-Chem model to identify the location from which BC arriving at a variety of locations in the Himalayas and Tibetan Plateau originates. We then calculate its direct and snow-albedo radiative forcing. We analyze the seasonal variation in the origin of BC using an adjoint sensitivity analysis, which provides a detailed map of the location of emissions that directly contribute to black carbon concentrations at receptor locations. We find that emissions from northern India and central China contribute the majority of BC to the Himalayas, although the precise location varies with season. The Tibetan Plateau receives most BC from western and central China, as well as from India, Nepal, the Middle East, Pakistan and other countries. The magnitude of contribution from each region varies with season and receptor location. We find that sources as varied as African biomass burning and Middle Eastern fossil fuel combustion can significantly contribute to the BC reaching the Himalayas and Tibetan Plateau. We compute radiative forcing in the snow-covered regions and find the forcing due to the BC induced snow-albedo effect to vary from 5–15 W m−2 within the region, an order of magnitude larger than radiative forcing due to the direct effect, and with significant seasonal variation in the northern Tibetan Plateau. Radiative forcing from reduced snow albedo likely accelerates glacier melting. Our analysis may help inform mitigation efforts to slow the rate of glacial melt by identifying regions that make the largest contributions to BC deposition in the Himalayas and Tibetan Plateau.
Avnery, Shiri, Denise L. Mauzerall+, Junfeng Liu, and Larry W. Horowitz. “Global Crop Yield Reductions due to Surface Ozone Exposure: 2. Year 2030 Potential Crop Production Losses and Economic Damage under Two Scenarios of O3 Pollution.” Atmospheric Environment 45 (2011): 2297-2309.Abstract
We examine the potential global risk of increasing surface ozone (O3) exposure to three key staple crops (soybean, maize, and wheat) in the near future (year 2030) according to two trajectories of O3 pollution: the Intergovernmental Panel on Climate Change Special Report on Emissions Scenarios (IPCC SRES) A2 and B1 storylines, which represent upper- and lower-boundary projections, respectively, of most O3 precursor emissions in 2030. We use simulated hourly O3 concentrations from the Model for Ozone and Related Chemical Tracers version 2.4 (MOZART-2), satellite-derived datasets of agricultural production, and field-based concentration:response relationships to calculate crop yield reductions resulting from O3 exposure. We then calculate the associated crop production losses and their economic value. We compare our results to the estimated impact of O3 on global agriculture in the year 2000, which we assessed in our companion paper [Avnery et al., 2011]. In the A2 scenario we find global year 2030 yield loss of wheat due to O3 exposure ranges from 5.4 to 26% (a further reduction in yield of þ1.5e10% from year 2000 values), 15e19% for soybean (reduction of þ0.9e11%), and 4.4e8.7% for maize (reduction of þ2.1e3.2%) depending on the metric used, with total global agricultural losses worth $17e35 billion USD2000 annually (an increase of þ$6e17 billion in losses from 2000). Under the B1 scenario, we project less severe but still substantial reductions in yields in 2030: 4.0e17% for wheat (a further decrease in yield of þ0.1e1.8% from 2000), 9.5e15% for soybean (decrease of þ0.7e1.0%), and 2.5e6.0% for maize (decrease of þ 0.3e0.5%), with total losses worth $12e21 billion annually (an increase of þ$1e3 billion in losses from 2000). Because our analysis uses crop data from the year 2000, which likely underestimates agricultural production in 2030 due to the need to feed a population increasing from approximately 6 to 8 billion people between 2000 and 2030, our calculations of crop production and economic losses are highly conservative. Our results suggest that O3 pollution poses a growing threat to global food security even under an optimistic scenario of future ozone precursor emissions. Further efforts to reduce surface O3 concentrations thus provide an excellent opportunity to increase global grain yields without the environmental degradation associated with additional fertilizer application or land cultivation.
Avnery, Shiri, Denise L. Mauzerall+, Junfeng Liu, and Larry W. Horowitz. “Global Crop Yield Reductions due to Surface Ozone Exposure: 1. Year 2000 Crop Production Losses and Economic Damage.” Atmospheric Environment 45 (2011): 2284-2296.Abstract
Exposure to elevated concentrations of surface ozone (O3) causes substantial reductions in the agricultural yields of many crops. As emissions of O3 precursors rise in many parts of the world over the next few decades, yield reductions from O3 exposure appear likely to increase the challenges of feeding a global population projected to grow from 6 to 9 billion between 2000 and 2050. This study estimates year 2000 global yield reductions of three key staple crops (soybean, maize, and wheat) due to surface ozone exposure using hourly O3 concentrations simulated by the Model for Ozone and Related Chemical Tracers version 2.4 (MOZART-2). We calculate crop losses according to two metrics of ozone exposure e seasonal daytime (08:00e19:59) mean O3 (M12) and accumulated O3 above a threshold of 40 ppbv (AOT40) e and predict crop yield losses using crop-specific O3 concentration:response functions established by field studies. Our results indicate that year 2000 O3-induced global yield reductions ranged, depending on the metric used, from 8.5e14% for soybean, 3.9e15% for wheat, and 2.2e5.5% for maize. Global crop production losses totaled 79e121 million metric tons, worth $11e18 billion annually (USD2000). Our calculated yield reductions agree well with previous estimates, providing further evidence that yields of major crops across the globe are already being substantially reduced by exposure to surface ozone e a risk that will grow unless O3-precursor emissions are curbed in the future or crop cultivars are developed and utilized that are resistant to O3. 2010 Kopp, RE, and DL Mauzerall+. “Assessing the climatic benefits of black carbon mitigation.” Proceedings of the National Academy of Sciences (2010).Abstract To limit mean global warming to 2 °C, a goal supported by more than 100 countries, it will likely be necessary to reduce emissions not only of greenhouse gases but also of air pollutants with high radiative forcing (RF), particularly black carbon (BC). Although several recent research papers have attempted to quantify the effects of BC on climate, not all these analyses have incorporated all the mechanisms that contribute to its RF (including the effects of BC on cloud albedo, cloud coverage, and snow and ice albedo, and the optical consequences of aerosol mixing) and have reported their results in different units and with different ranges of uncertainty. Here we attempt to reconcile their results and present them in uniform units that include the same forcing factors. We use the best estimate of effective RF obtained from these results to analyze the benefits of mitigating BC emissions for achieving a specific equilibrium temperature target. For a 500 ppm CO2e (3.1Wm−2) effective RF target in 2100, which would offer about a 50% chance of limiting equilibrium warming to 2.5 °C above preindustrial temperatures, we estimate that failing to reduce carbonaceous aerosol emissions from contained combustion would require CO2 emission cuts about 8 years (range of 1–15 years) earlier than would be necessary with full mitigation of these emissions. 2009 Saikawa, E, V. Naik, L. W. Horowitz, J Liu, and DL Mauzerall+. “Present and potential future contributions of sulfate, black and organic carbon aerosols from China to global air quality, premature mortality and radiative forcing.” Atmospheric Environment 43 (2009): 2814–2822.Abstract Aerosols are harmful to human health and have both direct and indirect effects on climate. China is a major contributor to global emissions of sulfur dioxide (SO2), a sulfate (SO4 2) precursor, organic carbon (OC), and black carbon (BC) aerosols. Although increasingly examined, the effect of present and potential future levels of these emissions on global premature mortality and climate change has not been well quantified. Through both direct radiative effects and indirect effects on clouds, SO4 2 and OC exert negative radiative forcing (cooling) while BC exerts positive forcing (warming). We analyze the effect of China’s emissions of SO2, SO4 2, OC and BC in 2000 and for three emission scenarios in 2030 on global surface aerosol concentrations, premature mortality, and radiative forcing (RF). Using global models of chemical transport (MOZART-2) and radiative transfer (GFDL RTM), and combining simulation results with gridded population data, mortality rates, and concentration–response relationships from the epidemiological literature, we estimate the contribution of Chinese aerosols to global annual premature mortality and to RF in 2000 and 2030. In 2000, we estimate these aerosols cause approximately 470 000 premature deaths in China and an additional 30 000 deaths globally. In 2030, aggressive emission controls lead to a 50% reduction in premature deaths from the 2000 level to 240 000 in China and 10 000 elsewhere, while under a high emissions scenario premature deaths increase 50% from the 2000 level to 720 000 in China and to 40 000 elsewhere. Because the negative RF from SO4 2 and OC is larger than the positive forcing from BC, Chinese aerosols lead to global net direct RF of 74 mW m2 in 2000 and between 15 and 97 mW m2 in 2030 depending on the emissions scenario. Our analysis indicates that increased effort to reduce greenhouse gases is essential to address climate change as China’s anticipated reduction of aerosols will result in the loss of net negative radiative forcing. Liu, J, DL Mauzerall+, and L. W. Horowitz. “Evaluating Inter-continental transport of fine aerosols: (2) Global Health Impacts.” Atmospheric Environment (2009).Abstract In this second of two companion papers, we quantify for the first time the global impact on premature mortality of the inter-continental transport of fine aerosols (including sulfate, black carbon, organic carbon, and mineral dust) using the global modeling results of (Liu et al., 2009). Our objective is to estimate the number of premature mortalities in each of ten selected continental regions resulting from fine aerosols transported from foreign regions in approximately year 2000. Our simulated annual mean population-weighted (P-W) concentrations of total PM2.5 (aerosols with diameter less than 2.5 mm) are highest in East Asia (EA, 30 mg m3 ) and lowest in Australia (3.6 mg m3 ). Dust is the dominant component of PM2.5 transported between continents. We estimate global annual premature mortalities (for adults age 30 and up) due to inter-continental transport of PM2.5 to be nearly 380 thousand (K) in 2000. Approximately half of these deaths occur in the Indian subcontinent (IN), mostly due to aerosols transported from Africa and the Middle East (ME). Approximately 90K deaths globally are associated with exposure to foreign (i.e., originating outside a receptor region) non-dust PM2.5. More than half of the premature mortalities associated with foreign non-dust aerosols are due to aerosols originating from Europe (20K), ME (18K) and EA (15K); and nearly 60% of the 90K deaths occur in EA (21K), IN (19K) and Southeast Asia (16K). The lower and higher bounds of our estimated 95% confidence interval (considering uncertainties from the concentration–response relationship and simulated aerosol concentrations) are 18% and 240% of the estimated deaths, respectively, and could be larger if additional uncertainties were quantified. We find that in 2000 nearly 6.6K premature deaths in North America (NA) were associated with foreign PM2.5 exposure (5.5K from dust PM2.5). NA is least impacted by foreign PM2.5 compared to receptors on the Eurasian continent. However, the number of premature mortalities associated with foreign aerosols in NA (mostly occurring in the U.S.) is comparable to the reduction in premature mortalities expected to result from tightening the U.S. 8-h O3 standard from 0.08 ppmv to 0.075 ppmv. International efforts to reduce inter-continental transport of fine aerosol pollution would substantially benefit public health on the Eurasian continent and would also benefit public health in the United States. Liu, J, DL Mauzerall+, L. W. Horowitz, P. Ginoux, and AM Fiore. “Evaluating Inter-continental transport of fine aerosols: (1) Methodology, global aerosol distribution and optical depth.” Atmospheric Environment (2009).Abstract Our objectives are to evaluate inter-continental source-receptor relationships for fine aerosols and to identify the regions whose emissions have dominant influence on receptor continents. We simulate sulfate, black carbon (BC), organic carbon (OC), and mineral dust aerosols using a global coupled chemistry-aerosol model (MOZART-2) driven with NCEP/NCAR reanalysis meteorology for 1997–2003 and emissions approximately representing year 2000. The concentrations of simulated aerosol species in general agree within a factor of 2 with observations, except that the model tends to overestimate sulfate over Europe in summer, underestimate BC and OC over the western and southeastern (SE) U.S. and Europe, and underestimate dust over the SE U.S. By tagging emissions from ten continental regions, we quantify the contribution of each region’s emissions on surface aerosol concentrations (relevant for air quality) and aerosol optical depth (AOD, relevant for visibility and climate) globally. We find that domestic emissions contribute substantially to surface aerosol concentrations (57–95%) over all regions, but are responsible for a smaller fraction of AOD (26–76%). We define ‘‘background’’ aerosols as those aerosols over a region that result from inter-continental transport, DMS oxidation, and emissions from ships or volcanoes. Transport from other continental source regions accounts for a substantial portion of background aerosol concentrations: 36–97% for surface concentrations and 38–89% for AOD. We identify the Region of Primary Influence (RPI) as the source region with the largest contribution to the receptor’s background aerosol concentrations (or AOD). We find that for dust Africa is the RPI for both aerosol concentrations and AOD over all other receptor regions. For non-dust aerosols (particularly for sulfate and BC), the RPIs for aerosol concentrations and AOD are identical for most receptor regions. These findings indicate that the reduction of the emission of non-dust aerosols and their precursors from an RPI will simultaneously improve both air quality and visibility over a receptor region. 2008 Liu, J, DL Mauzerall+, and L. W. Horowitz. “Source-Receptor Relationships between East Asian Sulfur Dioxide Emissions and Northern Hemisphere Sulfate Concentrations.” Atmos. Chem. Phys 8 (2008): 3721–3733. Publisher's VersionAbstract We analyze the effect of varying East Asian (EA) sulfur emissions on sulfate concentrations in the Northern Hemisphere, using a global coupled oxidant-aerosol model (MOZART-2). We conduct a base and five sensitivity simulations, in which sulfur emissions from each continent are tagged, to establish the source-receptor (S-R) relationship between EA sulfur emissions and sulfate concentrations over source and downwind regions. We find that from west to east across the North Pacific, EA sulfate contributes approximately 80%–20% of sulfate at the surface, but at least 50% at 500 hPa. Surface sulfate concentrations are dominated by local anthropogenic sources. Of the sulfate produced from sources other than local anthropogenic emissions (defined here as “background” sulfate), EA sources account for approximately 30%–50% (over the Western US) and 10%– 20% (over the Eastern US). The surface concentrations of sulfate from EA sources over the Western US are highest in MAM (up to 0.15µg/m3 ), and lowest in DJF (less than 0.06µg/m3 ). Reducing EA SO2 emissions will significantly decrease the spatial extent of the EA sulfate influence (represented by the areas where at least 0.1µg m−3 of sulfate originates from EA) over the North Pacific both at the surface and at 500 hPa in all seasons, but the extent of influence is insensitive to emission increases, particularly in DJF and JJA. We find that EA sulfate concentrations over most downwind regions respond nearly linearly to changes in EA SO2 emissions, but sulfate concentrations over the EA source region increase more slowly than SO2 emissions, particularly at the surface and in winter, due to limited availability of oxidants (in particular of H2O2, which oxidizes SO2 to sulfate in the aqueous phase). We find that similar estimates of the S-R relationship for trans-Pacific transport of EA sulfate would be obtained using either sensitivity (i.e., varying emissions from a region to examine the effects on downwind concentrations) or tagging techniques. Our findings suggest that future changes in EA sulfur emissions may cause little change in the sulfate-induced health impact over downwind continents. However, SO2 emission reductions may significantly reduce the sulfate concentrations and the resulting negative radiative forcing over the North Pacific and the United States, thus providing a warming tendency. Tong, DQ, and DL Mauzerall+. “Summertime State-Level Source-Receptor Relationships between Nitrogen Oxide Emissions and Downwind Surface Ozone Concentrations over the Continental United States.” Environmental Science & Technology (2008).Abstract Interstate transport of ozone (O3) and its precursors can contribute substantially to state-level surface O3 concentrations, making it difficult for some states to meet the National Ambient Air Quality Standards (NAAQS) for O3 by limiting only their own emissions. We analyze the effect of interstate transport on surface O3 in each continental U.S. state in July 1996 using the community multiscale air quality (CMAQ) model. By examining the difference between a baseline simulation and perturbation simulations in which each state’s nitrogen oxides (NOx) emissions are removed, we establish for the first time a summertime source-receptor matrixfor all 48 continental states. We find that for 16 (20) states at least one neighboring state’s NOx emissions are responsible for a larger increase in monthly mean peak 8 h (all-hour) O3 concentrations than the state’s own emissions. For over 80% of the contiguous states, interstatetransport is more importantthan local emissions for summertime peak O3 concentrations. Our source-receptor matrices indicate that the geographic range of the clean air interstate rule (CAIR) was sufficient to address interstate transport of O3 in most of the states included in the program. However, the exclusion of Texas, which has particularly large NOx emissions, from the CAIR O3 program left emission sources uncontrolled that contribute more than 1 ppbv to the July mean of peak8hO3 concentrations in over a dozen states. 2007 West, J.J., A.M. Fiore, V. Naik, L. W. Horowitz, M. D. Schwarzkopf, and D. L. Mauzerall. “Ozone Air Quality and Radiative Forcing Consequences of Changes in Ozone Precursor Emissions.” Geophys. Res. Lett. 34 (2007). Naik, V., D. L. Mauzerall, L. W. Horowitz, M. D. Schwarzkopf, V. Ramaswamy, and M. Oppenheimer. “Sensitivity of Radiative Forcing from Biomass Burning Aerosols and Ozone to Emission Location.” Geophys. Res. Lett. 34 (2007). Liu, J., and D. L. Mauzerall+. “Evaluating the potential influence of inter-continental transport of sulfate aerosols on air quality.” Environmental Research Letters 2 (2007). Publisher's Version 2006 Tong, D.Q., and D. L. Mauzerall. “Spatial variability of summertime tropospheric ozone over the continental United States: Implications of an evaluation of the CMAQ model.” Atmospheric Environment 40 (2006): 3041-3056.Abstract This study evaluates the ability of the Community Multiscale Air Quality (CMAQ) model to simulate the spatial variability of summertime ozone (O3) at the surface and in the free troposphere over the continental United States. Simulated surface O3 concentrations are compared with 987 Air Quality System (AQS) sites and 123 Clean Air Status and Trends Network (CASTNet) sites. CMAQ’s ability to reproduce surface observations varies with O3 concentration. The model best simulates observed O3 for intermediate concentrations (40–60 ppbv), while over-(under-) predicting at lower (higher) levels. CMAQ reproduces surface O3 for a wide range of conditions (30–80 ppbv) with a normalized mean error (NME) less than 35% and normalized mean bias (NMB) lying between 715% for the whole domain. Although systematically over-predicting O3 in the east and under-predicting it in the western United States, CMAQ is able to reproduce 1- and 8-h daily maxima with a cross-domain mean bias (MB) of 1 and 8 ppbv, or NMB of 8% and 25%, respectively. The model underestimates observed O3 at rural sites (MB ¼ 5 ppbv, NMB ¼ 5% and NME ¼ 23% with a 40 ppbv cut-off value) and over-predicts it at urban and suburban sites by a similar magnitude (MB ¼ 6 ppbv, NMB ¼ 7% and NME ¼ 25%). Apparent errors and biases decrease when data is averaged over longer periods, suggesting that most evaluation statistics are dependent on the time scale of data aggregation. Therefore, performance criteria should specify an averaging period (e.g., 1- or 8- h) and not be independent of averaging period as some current model evaluation studies imply. Comparisons of vertical profiles of simulated O3 with ozonesonde data show both overestimation and underestimation by 10–20 ppbv in the lower troposphere and a consistent under-prediction in the upper troposphere. Vertical O3 distributions are better simulated when lateral boundary conditions obtained from the global Model of Ozone and Related Tracers version 2 (MOZART-2) are used, but under-prediction remains. The assumption of zero-flux at the top boundary and the resulting exclusion of the contribution of stratosphere–troposphere exchange to tropospheric O3 concentrations limit the ability of CMAQ to reproduce O3 concentrations in the upper troposphere. r 2006 Elsevier Ltd. All rights reserved. Wang, X., and D. L. Mauzerall. “Evaluating Impacts of Air Pollution in China on Public Health: Implications for Future Air Pollution and Energy Policies.” Atmospheric Environment 40, no. 9 (2006): 1706-1721.Abstract Our objective is to establish the link between energy consumption and technologies, air pollution concentrations, and resulting impacts on public health in eastern China. We use Zaozhuang, a city in eastern China heavily dependent on coal, as a case study to quantify the impacts that air pollution in eastern China had on public health in 2000 and the benefits in improved air quality and health that could be obtained by 2020, relative to business-as-usual (BAU), through the implementation of best available emission control technology (BACT) and advanced coal gasification technologies (ACGT). We use an integrated assessment approach, utilizing state-of-the-science air quality and meteorological models, engineering, epidemiology, and economics, to achieve this objective. We find that total health damages due to year 2000 anthropogenic emissions from Zaozhuang, using the ‘‘willingness-to-pay’’ metric, was equivalent to 10% of Zaozhuang’s GDP. If all health damages resulting from coal use were internalized in the market price of coal, the year 2000 price would have more than tripled. With no new air pollution controls implemented between 2000 and 2020 but with projected increases in energy use, we estimate health damages from air pollution exposure to be equivalent to 16% of Zaozhuang’s projected 2020 GDP. BACT and ACGT (with only 24% penetration in Zaozhuang and providing 2% of energy needs in three surrounding municipalities) could reduce the potential health damage of air pollution in 2020 to 13% and 8% of projected GDP, respectively. Benefits to public health, of substantial monetary value, can be achieved through the use of BACT; health benefits from the use of ACGT could be even larger. Despite significant uncertainty associated with each element of the integrated assessment approach, we demonstrate that substantial benefits to public health could be achieved in this region of eastern China through the use of additional pollution controls and particularly from the use of advanced coal gasification technology. Without such controls, the impacts of air pollution on public health, presently considerable, will increase substantially by 2020. Tong, D.Q., N.Z. Muller, D. L. Mauzerall, and R.O. Mendelsohn. “Integrated Assessment of the Spatial Variability of Ozone Impacts from Emissions of Nitrogen Oxides.” Environmental Science and Technology 40, no. 5 (2006): 1395-1400.Abstract This paper examines the ozone (O3) damages caused by nitrogen oxides (NOx) emissions in different locations around the Atlanta metropolitan area during a summer month. We calculate O3 impacts using a new integrated assessment model that links pollution emissions to their chemical transformation, transport, population exposures, and effects on human health. We find that increased NOx emissions in rural areas around Atlanta increase human exposure to ambient O3 twice as much as suburban emissions. However, increased NOx emissions in central city Atlanta actually reduce O3 exposures. For downtown emissions, the reduction in human exposures to O3 from titration by NO in the central city outweighs the effects from increased downwind O3. The results indicate that the marginal damage from NOx emissions varies greatly across a metropolitan area. The results raise concerns if cap and trade regulations cause emissions to migrate toward higher marginal damage locations. West, J.J., A. F. Fiore, L. W. Horowitz, and D. L. Mauzerall. “Mitigating Ozone Pollution with Methane Emission Controls: Global Health Benefits.” Proceedings of the National Academy of Science 103, no. 11 (2006).Abstract Methane (CH4) contributes to the growing global background concentration of tropospheric ozone (O3), an air pollutant associated with premature mortality. Methane and ozone are also important greenhouse gases. Reducing methane emissions therefore decreases surface ozone everywhere while slowing climate warming, but although methane mitigation has been considered to address climate change, it has not for air quality. Here we show that global decreases in surface ozone concentrations, due to methane mitigation, result in substantial and widespread decreases in premature human mortality. Reducing global anthropogenic methane emissions by 20% beginning in 2010 would decrease the average daily maximum 8-h surface ozone by 1 part per billion by volume globally. By using epidemiologic ozonemortality relationships, this ozone reduction is estimated to prevent 30,000 premature all-cause mortalities globally in 2030, and 370,000 between 2010 and 2030. If only cardiovascular and respiratory mortalities are considered, 17,000 global mortalities can be avoided in 2030. The marginal cost-effectiveness of this 20% methane reduction is estimated to be$420,000 per avoided mortality. If avoided mortalities are valued at $1 million each, the benefit is$240 per tonne of CH4 ($12 per tonne of CO2 equivalent), which exceeds the marginal cost of the methane reduction. These estimated air pollution ancillary benefits of climate-motivated methane emission reductions are comparable with those estimated previously for CO2. Methane mitigation offers a unique opportunity to improve air quality globally and can be a cost-effective component of international ozone management, bringing multiple benefits for air quality, public health, agriculture, climate, and energy. 2005 Liu, J., D. L. Mauzerall, and L. W. Horowitz. “Analysis of Seasonal and Interannual Variability in Transpacific Transport.” J. Geophys. Res. 110, no. D04302 (2005).Abstract The purpose of our analysis is both to evaluate the meteorological component of the seasonal and interannual variability of transpacific transport and to identify meteorological features that can be used to estimate transpacific transport. To accomplish this goal, we simulate the transport of nine continental tracers with uniform emissions and two-week lifetimes using the global Model of Ozone and Related Tracers Version 2 (MOZART-2) driven with NCEP reanalysis meteorology from 1991–2001. In addition, we define a transpacific ‘‘transport potential,’’ a measure of the quantity of a tracer transported from a particular region normalized by its total emissions from that region, across a meridional plane in the eastern Pacific at 130W. We find that at midlatitudes, the east Asian and Indian tracers have the largest transport potentials, particularly in spring. The interannual variability of the transpacific transport potentials of most tracers is relatively high in winter and fall (particularly in February and September) but is low from April to August. At high latitudes the former Soviet Union, east Asian, and European tracers have the largest transpacific transport potentials, especially in late summer and fall, when the lowest interannual variability is observed. We find that El Nin˜o winters are associated with stronger eastward transport of east Asian emissions in the subtropical eastern Pacific. Transport of the east Asian tracer in the central North Pacific is well correlated with the North Pacific Index. However, we find that the interannual variability of transport across the west coast of North America is mostly driven by local meteorology. We therefore created a new index based on meteorology over the eastern Pacific, which we call the Eastern Pacific Index (EPI). The EPI captures most of the interannual variability of transpacific transport at both middle- and high-latitude regions across the west coast of North America. Liu, J., and D. L. Mauzerall. “Estimating the Average Time for Inter-continental Transport of Air Pollutants.” Geophysical Research Letters 32, no. L11814 (2005).Abstract We estimate the average time required for intercontinental transport of atmospheric tracers based on simulations with the global chemical tracer model MOZART-2 driven with NCEP meteorology. We represent the average transport time by a ratio of the concentration of two tracers with different lifetimes. We find that average transport times increase with tracer lifetimes. With tracers of 1- and 2-week lifetimes the average transport time from East Asia (EA) to the surface of western North America (NA) in April is 2 – 3 weeks, approximately a half week longer than transport from NA to western Europe (EU) and from EU to EA. We develop an ‘equivalent circulation’ method to estimate a timescale which has little dependence on tracer lifetimes and obtain similar results to those obtained with short-lived tracers. Our findings show that average intercontinental transport times, even for tracers with short lifetimes, are on average 1 – 2 weeks longer than rapid transport observed in plumes. Mauzerall, D. L, B. Sultan, J Kim, and D. Bradford. “NOx Emissions: Variability in Ozone Production, Resulting Health Damages and Economic Costs.” Atmospheric Environment 39, no. 16 (2005): 2851-2866.Abstract We present a proof-of-concept analysis of the measurement of the health damage of ozone (O3) produced from nitrogen oxides ðNOx ¼ NO þ NO2Þ emitted by individual large point sources in the eastern United States. We use a regional atmospheric model of the eastern United States, the Comprehensive Air quality Model with Extensions (CAMx), to quantify the variable impact that a fixed quantity of NOx emitted from individual sources can have on the downwind concentration of surface O3, depending on temperature and local biogenic hydrocarbon emissions. We also examine the dependence of resulting O3-related health damages on the size of the exposed population. The investigation is relevant to the increasingly widely used ‘‘cap and trade’’ approach to NOx regulation, which presumes that shifts of emissions over time and space, holding the total fixed over the course of the summer O3 season, will have minimal effect on the environmental outcome. By contrast, we show that a shift of a unit of NOx emissions from one place or time to another could result in large changes in resulting health effects due to O3 formation and exposure. We indicate how the type of modeling carried out here might be used to attach externality-correcting prices to emissions. Charging emitters fees that are commensurate with the damage caused by their NOx emissions would create an incentive for emitters to reduce emissions at times and in locations where they cause the largest damage. Wang, Xiaoping, Denise L. Mauzerall, Yongtao Hu, Armistead G. Russell, Eric D. Larson, Jung-Hun Woo, David G. Streets, and Alex Guenther. “A high-resolution emission inventory for eastern China in 2000 and three scenarios for 2020.” Atmospheric Environment 39, no. 32 (2005): 5917-5933.Abstract We develop a source-specific high-resolution emission inventory for the Shandong region of eastern China for 2000 and 2020. Our emission estimates for year 2000 are higher than other studies for most pollutants, due to our inclusion of rural coal consumption, which is significant but often underestimated. Still, our inventory evaluation suggests that we likely underestimate actual emissions. We project that emissions will increase greatly from 2000 to 2020 if no additional emission controls are implemented. As a result, PM2.5 concentrations will increase; however O3 concentrations will decrease in most areas due to increased NOx emissions and VOC-limited O3 chemistry. Taking Zaozhuang Municipality in this region as a case study, we examine possible changes in emissions in 2020 given projected growth in energy consumption with no additional controls utilized (BAU), with adoption of best available end-of-pipe controls (BACT), and with advanced, low-emission coal gasification technologies (ACGT) which are capable of gasifying the high-sulfur coal that is abundant in China. Emissions of NH3 are projected to be 20% higher, NMVOC50% higher, and all other species 130–250% higher in 2020 BAU than in 2000. Both alternative 2020 emission scenarios would reduce emissions relative to BAU. Adoption of ACGT, which meets only 24% of energy service demand in Zaozhuang in 2020 would reduce emissions more than BACT with 100% penetration. In addition, coal gasification technologies create an opportunity to reduce greenhouse gas emissions by capturing and sequestering CO2 emissions below ground. Tong, D.Q., and D. L. Mauzerall. “Technical Note: Numerical instability in the Community Multi-scale Air Quality model and its impacts on aerosol and ozone simulations.” Atmospheric Environment (2005).Abstract This paper reports a numerical instability problem in the widely used Community Multiscale Air Quality (CMAQ) model and discusses its impacts on ozone and particulate matter simulations. By adding 0.5 moles/sec of NO x emissions to Middlesex County, CT, for example, CMAQ (2003 version) predicts up to 1 μg/m 3 change in PM 2.5 concentrations in the Ohio Valley and southern California in less then 48 hours. These regions are beyond the reach of normal transport processes in such a short time, and the remote and upwind responses are 100 times larger than responses near or downwind of the source area. More recently, progress has been made in reducing the numerical instability by correcting coding errors in the transport algorithm, adopting additional vertical wind adjustment to enhance mass conservation, and making numerous improvements in the ISSOROPIA aerosol thermodynamics module (2004 and 2005 CMAQ versions). These improvements, however, are not sufficient to reduce the instability to a reasonable level. The magnitude of peak instability in the 2005 version of CMAQ remains comparable to the normal responses from NO x emissions of a middle-size power plant. This problem, although having a minor effect on the model performance to simulate total O 3 and PM concentrations, results in difficulties when the current version of CMAQ is used to address many important air quality issues including localized emission controls and source-receptor simulations. Naik, V., D. L. Mauzerall, L. W. Horowitz, D. Schwarzkopf, V. Ramaswamy, and M. Oppenheimer. “Net Radiative Forcing Due to Changes in Regional Emissions to Tropospheric Ozone Precursors.” Journal of Geophysical Research 110 (2005).Abstract The global distribution of tropospheric ozone (O3) depends on the emission of precursors, chemistry, and transport. For small perturbations to emissions, the global radiative forcing resulting from changes in O3 can be expressed as a sum of forcings from emission changes in different regions. Tropospheric O3 is considered in present climate policies only through the inclusion of indirect effect of CH4 on radiative forcing through its impact on O3 concentrations. The short-lived O3 precursors (NOx, CO, and NMHCs) are not directly included in the Kyoto Protocol or any similar climate mitigation agreement. In this study, we quantify the global radiative forcing resulting from a marginal reduction (10%) in anthropogenic emissions of NOx alone from nine geographic regions and a combined marginal reduction in NOx, CO, and NMHCs emissions from three regions. We simulate, using the global chemistry transport model MOZART-2, the change in the distribution of global O3 resulting from these emission reductions. In addition to the short-term reduction in O3, these emission reductions also increase CH4 concentrations (by decreasing OH); this increase in CH4 in turn counteracts part of the initial reduction in O3 concentrations. We calculate the global radiative forcing resulting from the regional emission reductions, accounting for changes in both O3 and CH4. Our results show that changes in O3 production and resulting distribution depend strongly on the geographical location of the reduction in precursor emissions. We find that the global O3 distribution and radiative forcing are most sensitive to changes in precursor emissions from tropical regions and least sensitive to changes from midlatitude and high-latitude regions. Changes in CH4 and O3 concentrations resulting from NOx emission reductions alone produce offsetting changes in radiative forcing, leaving a small positive residual forcing (warming) for all regions. In contrast, for combined reductions of anthropogenic emissions of NOx, CO, and NMHCs, changes in O3 and CH4 concentrations result in a net negative radiative forcing (cooling). Thus we conclude that simultaneous reductions of CO, NMHCs, and NOx lead to a net reduction in radiative forcing due to resulting changes in tropospheric O3 and CH4 while reductions in NOx emissions alone do not. 2004 Wang, X., and D. L. Mauzerall. “Characterizing Distributions of Surface Ozone and its Impact on Grain Production in China, Japan and South Korea: 1990 and 2020.” Atmospheric Environment 38 (2004): 4383-4402.Abstract Using an integrated assessment approach, we evaluate the impact that surface O3 in East Asia had on agricultural production in 1990 and is projected to have in 2020. We also examine the effect that emission controls and the enforcement of environmental standards could have in increasing grain production in China. We find that given projected increases in O3 concentrations in the region, East Asian countries are presently on the cusp of substantial reductions in grain production. Our conservative estimates, based on 7- and 12-h mean (M7 or M12) exposure indices, show that due to O3 concentrations in 1990 China, Japan and South Korea lost 1–9% of their yield of wheat, rice and corn and 23–27% of their yield of soybeans, with an associated value of 1990US$ 3.5, 1.2 and 0.24 billion, respectively. In 2020, assuming no change in agricultural production practices and again using M7 and M12 exposure indices, grain loss due to increased levels of O3 pollution is projected to increase to 2–16% for wheat, rice and corn and 28–35% for soybeans; the associated economic costs are expected to increase by 82%, 33%, and 67% in 2020 over 1990 for China, Japan and South Korea, respectively. For most crops, the yield losses in 1990 based on SUM06 or W126 exposure indices are lower than yield losses estimated using M7 or M12 exposure indices in China and Japan but higher in South Korea; in 2020, the yield losses based on SUM06 or W126 exposure indices are substantially higher for all crops in all three countries. This is primarily due to the nature of the cumulative indices which weight elevated values of O3 more heavily than lower values. Chinese compliance with its ambient O3 standard in 1990 would have had a limited effect in reducing the grain yield loss caused by O3 exposure, resulting in only US$0.2 billion of additional grain revenues, but in 2020 compliance could reduce the yield loss by one third and lead to an increase of US$ 2.6 (M7 or M12) –27 (SUM06) billion in grain revenues. We conclude that East Asian countries may have tremendous losses of crop yields in the near future due to projected increases in O3 concentrations. They likely could achieve substantial increases in future agricultural production through reduction of surface O3 concentrations and/or use of O3 resistant crop cultivars. r 2004 Elsevier Ltd. All rights reserved.
2003
Horowitz, L. W., S. Walters, D. L. Mauzerall, L.K. Emmons, P.J. Rasch, C. Granier, X. Tie, et al.A Global Simulation of Tropospheric Ozone and Related Tracers: Description and Evaluation of MOZART, Version 2.” Journal of Geophysical Research 108, no. D24 (2003): 4784.Abstract
We have developed a global three-dimensional chemical transport model called Model of Ozone and Related Chemical Tracers (MOZART), version 2. This model, which will be made available to the community, is built on the framework of the National Center for Atmospheric Research (NCAR) Model of Atmospheric Transport and Chemistry (MATCH) and can easily be driven with various meteorological inputs and model resolutions. In this work, we describe the standard configuration of the model, in which the model is driven by meteorological inputs every 3 hours from the middle atmosphere version of the NCAR Community Climate Model (MACCM3) and uses a 20-min time step and a horizontal resolution of 2.8 latitude 2.8 longitude with 34 vertical levels extending up to approximately 40 km. The model includes a detailed chemistry scheme for tropospheric ozone, nitrogen oxides, and hydrocarbon chemistry, with 63 chemical species. Tracer advection is performed using a flux-form semi-Lagrangian scheme with a pressure fixer. Subgrid-scale convective and boundary layer parameterizations are included in the model. Surface emissions include sources from fossil fuel combustion, biofuel and biomass burning, biogenic and soil emissions, and oceanic emissions. Parameterizations of dry and wet deposition are included. Stratospheric concentrations of several long-lived species (including ozone) are constrained by relaxation toward climatological values. The distribution of tropospheric ozone is well simulated in the model, including seasonality and horizontal and vertical gradients. However, the model tends to overestimate ozone near the tropopause at high northern latitudes. Concentrations of nitrogen oxides (NOx) and nitric acid (HNO3) agree well with observed values, but peroxyacetylnitrate (PAN) is overestimated by the model in the upper troposphere at several locations. Carbon monoxide (CO) is simulated well at most locations, but the seasonal cycle is underestimated at some sites in the Northern Hemisphere. We find that in situ photochemical production and loss dominate the tropospheric ozone budget, over input from the stratosphere and dry deposition. Approximately 75% of the tropospheric production and loss of ozone occurs within the tropics, with large net production in the tropical upper troposphere. Tropospheric production and loss of ozone are three to four times greater in the northern extratropics than the southern extratropics. The global sources of CO consist of photochemical production (55%) and direct emissions (45%). The tropics dominate the chemistry of CO, accounting for about 75% of the tropospheric production and loss. The global budgets of tropospheric ozone and CO are generally consistent with the range found in recent studies. The lifetime of methane (9.5 years) and methylchloroform (5.7 years) versus oxidation by tropospheric hydroxyl radical (OH), two useful measures of the global abundance of OH, agree well with recent estimates. Concentrations of nonmethane hydrocarbons and oxygenated intermediates (carbonyls and peroxides) generally agree well with observations.
2000
Mauzerall, Denise L., D. Narita, H. Akimoto, L. Horowitz, S. Walters, D. Hauglustaine, and B. Brasseur. “Seasonal Characteristics of Tropospheric Ozone Production and Mixing Ratios Over East Asia: A Global Three-dimensional Chemical Transport Model Analysis.” Journal of Geophysical Research 105 (2000): 17895-17910.Abstract
We examine seasonal and geographical distributions of tropospheric ozone production and mixing ratios over East Asia with a global three-dimensional chemical transport model called Model of Ozone and Related Tracers, version 1 (MOZART-1). Net ozone production within the East Asian boundary layer exhibits three distinct seasonal cycles depending on region (north of 20N, 5-20N and south of 5N). North of 20N, net ozone production over East Asia from spring through autumn is found to have a maximum extending from 25N-40N and from central eastern China to Japan, resulting from the strong emission and transport of anthropogenic O3 precursors. In winter, maximum O3 production in this region occurs between 20N and 30N. This is a region of long-range transport. Over the Indochina peninsula, between 5N and 20N, net O3 production is controlled by the seasonal cycle between wet and dry seasons and has a maximum at the end of the dry season due to emissions from biomass burning. South of 5N, in the true tropics, O3 mixing ratios are relatively constant throughout the year and do not exhibit a seasonal cycle. A spring-summer maximum of net O3 production is found throughout the troposphere in East Asia. We estimate an annual net O3 production in East Asia of 117 Tg/yr. Both model results and analysis of measurements of O3-CO correlations over East Asia and Japan show strong variability as a function of both photochemical activity and seasonal meteorology, and indicate ozone export off the coast of East Asia in spring. An upper estimate of O3 export from East Asia to the Pacific Ocean in the mid-1980s of 3.3 Gmol/day (58 Tg/yr) is obtained.
1998
Mauzerall, Denise L., J. A. Logan, D. J. Jacob, B. E. Anderson, D. R. Blake, J. D. Bradshaw, G. W. Sachse, H. B. Singh, and R. W. Talbot. “Photochemistry in Biomass Burning Plumes and Implications for Tropospheric Ozone Over the Tropical South Atlantic.” Journal of Geophysical Research 103 (1998): 8401-8423.Abstract
We quantify the tropospheric ozone budget over remote high northern latitudes in summer using chemical and meteorological measurements between 0 and 6-km made during the summer 1990 Arctic Boundary Layer Expedition (ABLE-3B). We include all components of the ozone budget, both sinks (in situ photochemical loss and deposition); and sources (in situ photochemical production, advection of pollution ozone into the region, production in biomass wildfire plumes, and downwards transport from the upper troposphere/stratosphere). In situ production and loss of ozone are calculated with a photochemical model. The net influx of pollution ozone from North America and Eurasia is estimated from the average enhancement ratio of DO3/DC2Cl4 observed in pollution plumes and scaled by the net influx of C2Cl4. The contribution of ozone produced in biomass wildfire plumes is estimated from the average enhancement ration of DO3/DCO in aged fire plumes. Regional photochemical production and loss in the 0-6 km column are found to be approximately equal; hence, net photochemical production is near zero. However, when ozone production and loss terms are separated, we find that dispersed in situ photochemical production driven by background NOx levels (5-10 pptv) is the largest source term in the ozone budget (62%). Influx of stratospheric ozone is of secondary importance (27%), long-range transport of pollution ozone makes a small contribution (9%), and photochemical production of ozone within biomass wildfire plumes is a relatively negligible term (2%) in the budget. Biomass fires and transport of anthropogenic pollution in the region may however have a major effect on the ozone budget through enhancement of background NOx mixing ratios which increase dispersed photochemical production. Using a 1-D time-dependent photochemical model between 0 and 6 km, we obtain good agreement between the observed and model-generated vertical ozone profiles. We find that in situ photochemistry within the 0-6 km column accounts for nearly 90% of the ozone mixing ratio within the boundary layer, while above 5 km it accounts for only about 40%. Although photochemical production of ozone within the 0-6 km column is larger than the other source terms combined, the 1-D model results indicate that influx from above is necessary to account for the observed increase in ozone mixing ratios with altitude.
1996
Jacob, D. J., B. G. Heikes, S. M. Fan, J. A. Logan, D. L. Mauzerall, J. D. Bradshaw, R. W. Talbot, D. R. Blake, and G. W. Sachse. “Origin of Ozone and NOx in the Tropical Troposphere: A Photochemical Analysis of Aircraft Observations Over the South Atlantic Basin.” Journal of Geophysical Research 101 (1996): 24235-24250.Abstract
The photochemistry of the troposphere over the South Atlantic Basin is examined by modeling of aircraft observations up to 12-km altitude from the TRACE-A expedition in September-October 1992. A close balance is found in the 0-12 km column between photochemical production and loss of O3, with net production at high altitudes compensating for weak net loss at low altitudes. Simulation of H2O2, CH3OOH, and CH2O concentrations measured aboard the aircraft lends confidence in the computations of O3 production and loss rates. Influx from the stratosphere is negligible as a source of O3 or NOx to the 0-12 km column. The primary sources of NOx appear to be continental (combustion, lightning, soils) and include a major contribution from biomass burning. There is evidence that NOx throughout the 0-12 km column is recycled from its oxidation products rather than directly transported from its primary sources. There is also evidence for rapid conversion of HNO3 to NOx in the upper troposphere by a mechanism not included in current models. A general representation of the O3 budget in the tropical troposphere is proposed that couples the large-scale Walker circulation and in situ photochemistry. Deep convection in the rising branches of the Walker circulation injects NOx from combustion, soils, and lightning to the upper troposphere, leading to O3 production; eventually the air subsides and net O3 loss takes place in the lower troposphere, closing the O3 cycle. This scheme implies a great sensitivity of the oxidizing power of the atmosphere to NOx emissions in the tropics.
Mauzerall, Denise L., D. J. Jacob, S. M. Fan, J. D. Bradshaw, G. L. Gregory, G. W. Sachse, and D. R. Blake. “Origin of Tropospheric Ozone at Remote High Northern Latitudes in Summer.” Journal of Geophysical Research 101 (1996): 4175-4188.Abstract
We quantify the tropospheric ozone budget over remote high northern latitudes in summer using chemical and meteorological measurements between 0 and 6-km made during the summer 1990 Arctic Boundary Layer Expedition (ABLE-3B). We include all components of the ozone budget, both sinks (in situ photochemical loss and deposition); and sources (in situ photochemical production, advection of pollution ozone into the region, production in biomass wildfire plumes, and downwards transport from the upper troposphere/stratosphere). In situ production and loss of ozone are calculated with a photochemical model. The net influx of pollution ozone from North America and Eurasia is estimated from the average enhancement ratio of DO3/DC2Cl4 observed in pollution plumes and scaled by the net influx of C2Cl4. The contribution of ozone produced in biomass wildfire plumes is estimated from the average enhancement ration of DO3/DCO in aged fire plumes. Regional photochemical production and loss in the 0-6 km column are found to be approximately equal; hence, net photochemical production is near zero. However, when ozone production and loss terms are separated, we find that dispersed in situ photochemical production driven by background NOx levels (5-10 pptv) is the largest source term in the ozone budget (62%). Influx of stratospheric ozone is of secondary importance (27%), long-range transport of pollution ozone makes a small contribution (9%), and photochemical production of ozone within biomass wildfire plumes is a relatively negligible term (2%) in the budget. Biomass fires and transport of anthropogenic pollution in the region may however have a major effect on the ozone budget through enhancement of background NOx mixing ratios which increase dispersed photochemical production. Using a 1-D time-dependent photochemical model between 0 and 6 km, we obtain good agreement between the observed and model-generated vertical ozone profiles. We find that in situ photochemistry within the 0-6 km column accounts for nearly 90% of the ozone mixing ratio within the boundary layer, while above 5 km it accounts for only about 40%. Although photochemical production of ozone within the 0-6 km column is larger than the other source terms combined, the 1-D model results indicate that influx from above is necessary to account for the observed increase in ozone mixing ratios with altitude.