My research program addresses the following central questions:
- What are present and potential future regional and global levels of air pollution? How significant is long-range transport of air pollution?
- What are/will be the impacts of air pollution on human health and welfare including impacts on agriculture and climate?
- What are appropriate air pollution mitigation policies that maximize co-benefits for human health, agriculture and climate change?
I seek to answer these questions through research projects at the global, regional and national scales. To address the first question, my group uses computer models of regional and global atmospheric chemistry, transport and radiation to simulate the emissions of air pollutants, their chemical transformation and movement around the world. We address the second question using tools drawn from epidemiology, agronomy, engineering and economics. Answers to the first two questions facilitate identification of air pollution mitigation policies that maximize co-benefits for air quality, health and climate change. My approach is to use rigorous scientific tools to address technical questions of direct policy relevance.
My research analyzes the impacts of air pollution in both the largest rapidly industrializing country (China) and in the largest developed country (US). On a global scale we investigate the inter-continental transport of air pollutants with an emphasis on transport from rapidly industrializing Asia to the rest of the world. On a regional scale, our recent work has examined the origin of black carbon reaching the Himalayas and Tibetan plateau and its effect on radiative forcing. We also examine the effect of air pollutants, particularly black carbon and ozone, on public health, agriculture and climate change. These issues are interlinked, globally pervasive and addressing one provides opportunities for leveraging solutions to others.
Scientific analysis is a vital prerequisite to the development of sound environmental policy responses in the above areas. Rarely will an atmospheric scientist venture into the policy arena and rarely will a policy maker understand the details of atmospheric science. Research frequently remains within a single discipline. However, in order to address the deleterious effects of air pollution on climate change, human health, and welfare, to examine the costs imposed on society by these effects, and to explore energy technology and policy options for encouraging more desirable outcomes, interdisciplinary research is critical. My group’s research, together with our collaborators, maintains depth in atmospheric science and utilizes tools from public health and agronomy, engineering and economics to inform the development of appropriate environmental policy. Our research to date has made significant interdisciplinary contributions and has laid an unusually strong foundation to address further questions at the intersection of atmospheric science and policy.
An overview of key research areas and future goals is below.
To slow the rate of climate warming and avoid “dangerous anthropogenic interference with the climate system”, 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) which is commonly known as “soot”. There are large uncertainties, however, in both the magnitude of black carbon’s RF and in the origin of BC reaching the Himalayan and Tibetan Plateau glaciers. These glaciers are important water sources for much of south and east Asia. Our recent work has helped reconcile recent estimates of RF of BC and has identified the regions which are major contributors to BC reaching the Asian glaciers.
Due to population growth, industrialization and increasing fossil fuel consumption, China is experiencing serious and worsening air pollution and is of strategic importance in determining future background levels of air pollution in the northern hemisphere. China is also now the largest emitter of greenhouse gasses in the world.
Through identification of local damages to public health and agriculture my group's research has worked to inform the development of future energy and environmental policies which reduce emissions of both reactive airpollutants and greenhouse gasses, and hence have both local and global co-benefits. We have performed amont the first integrated assessments of air pollution impacts in Asia. Our integrated assessment approach incorporates emission estimates, modeling of atmospheric transport and radiative forcing, exposure-response relationships and economics to estimate the value of environmental damages due to air pollution. Although uncertainties exist at each step of such an assessment, the approach allows us to quantitatively link emissions, with concentrations of air pollutants in the atmosphere, with exposures, with impacts and utilmately with technology/policy options that reduce damages from emissions.
For research on the impace of ozone on crop yields in China, please see the section on agriculture.
3) is well documented as the air pollutant most damaging to agricultural crops and other plants. Most crops are grown in summer when ozone concentrations are frequently sufficiently elevated to reduce yields. Work in my group has examined impacts of present and potential future surface O
3 concentrations in East Asia and globally on agricultural yields. Although sensitivity to O
3 varies by crop type, for soybeans and wheat we found significant yield reductions at present and project substantial yield reductions globally by 2030.
As Asia industrializes there is increasing concern in the United States over the impact that long-range transport of Asian emissions will have on air quality in the US. Important questions are whether the effect will be felt primarily by rising background concentrations of air pollution in the northern hemisphere or by occasional rapidly transported pollution plumes, and how large the seasonal and inter-annual variability in transport will be. Our results are important because they provide insight into transport characteristics which determine how significant and how variable the impact of Asian emissions will be on US air quality and on public health.
Reductions in methane (CH
4) emissions decrease greenhouse warming; we show that they also decrease surface ozone concentrations globally, and consequently, reduce premature mortalities due to ozone exposure. By combining global atmospheric modeling, health effects assessment, and economics, our work quantifies the previously unrecognized co-benefits of methane mitigation for air quality and human mortality at ~$240 per ton methane (~$12 per ton carbon dioxide equivalent). Methane mitigation is cost-effective for air quality management, and because it affects ozone globally, methane provides a first means of directly managing global air quality. We also find that, of the available means to improve O
3 air quality through reductions in the emission of O
3precursors (NOx, non-methane hydrocarbons, carbon monoxide or CH
4 abatement best reduces climate forcing. Our research is uniquely interdisciplinary, with broad relevance for air quality, climate, public health, and environmental policy.
Current “cap-and-trade” regulations in the US limit total nitrogen oxide (NOx) emissions in order to control ozone concentrations. These regulations implicitly assume that the damage caused by the emission of a unit of NOx is independent of when (during the summer ozone season) and where it is emitted. We used regional atmospheric modeling to demonstrate that when and where NOx is emitted, in fact, has a large impact on the quantity of ozone produced. Using epidemiological concentration-response relationships we also showed that ozone-related premature mortalities and morbidities vary with the size of the exposed population. Thus 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 ozone formation and exposure. As a policy alternative to a cap on emissions, we propose charging emitters fees that are commensurate with the damage their emissions cause. This would create an incentive for emitters to reduce emissions at times and in locations where they cause the largest damage.
Air pollutants impact human health and welfare; they can also influence climate change. From a policy perspective it would be advantageous to be able to credit countries for reducing their emission of air pollutants that contribute to climate warming and thus to secure both local and global benefits. However, determining the impact that emissions of short-lived air pollutants have on climate is challenging for several reasons. First, when and where they are emitted influences the impact they have on climate. Second, they interact in the atmosphere resulting in increases in the concentrations of certain gases and decreases in the concentrations of others with the net change determining the climate effect. We examined the influence of location of anthropogenic emissions and biomass burning on their impact on direct radiative forcing.
Complementing courses I’ve taught on sustainable development is a research project examining the efficacy of partnerships between governments, industry and non-governmental organizations in furthering the goals of sustainable development.
Future Research Goals
My past research has addressed critical questions at the intersection of atmospheric science and environmental policy both in the US, Asia and globally. Although these issues may seem overwhelming in their complexity, advances in computational modeling have made attempts to study and to identify scientifically supportable policy options both feasible and realistic. Establishing limits and confidence levels on these predictions is important. Linking the findings with policy development is vital.
I wish to build on our unusual ability to use sophisticated models of regional and global atmospheric chemistry, transport and radiation to evaluate the benefits to human health and welfare of various policy options. Planned research will begin to utilize coupled chemistry-climate models to improve understanding of the role of air pollution on climate change. Future research in my group should contribute to identification of policies which lead to both local and global benefits through the strategic reduction of the emission of reactive air pollutants and greenhouse gases. Some specific research goals are described below.
Climate and Black Carbon – Sectoral analysis of mitigation strategies; Himalayas, Arctic; health impacts in source regions.
I plan to use the GEOS-Chem adjoint model to conduct a sectoral analysis of the origin of BC reaching the Asian glaciers in order to identify key emission sectors in the locations that have the largest climate impact. This work will be done in conjunction with an analysis of the health impacts of the BC emissions within the key source regions impacting the Himalayas. The objective will be to motivate efforts to reduce BC emissions in regions from which the BC is transported to the glaciers. Our method will be to first identify the locations and emission sectors that result in the largest amounts of BC reaching the Asian glaciers. Our second step will be to calculate the impact of those BC emissions near the source on morbidity and premature mortality.
The Arctic has warmed at almost twice the global average rate over the past century and BC deposition is likely contributing to that accelerated rate. I wish to conduct a similar adjoint and health impact analysis for BC reaching the Arctic to determine both the spatial and sectoral origins of the BC in the Arctic and to identify desirable mitigation targets that maximize co-benefits for public health and climate change.
Agriculture – comparison of O
3 and climate impacts; benefit of methane mitigation; and analysis of other O
3 mitigation strategies
In order to put the magnitude and spatial extent of crop losses due to O
3 exposure in a larger context I plan to compare global estimates of yield losses due to O
3 exposure with similar projected losses due to climate change that have been reported in the literature. In addition, to identify optimal mitigation strategies to reduce surface O
3 and protect agriculture in regions of the world where crops are projected to suffer significant crop yield losses I plan to use adjoint sensitivity analysis to quantify O
3 sensitivity to precursor emissions (including species, source type (anthropogenic vs. natural), geographic origin, and timing of emissions) in locations where significant crop losses were identified to occur in Avnery et al. (2010a and 2010b). To augment this analysis we will also explore the use of satellite data to quantify the ratio of formaldehyde (HCHO) to NO
2 column amounts, which have been demonstrated to be a reliable technique to diagnose NOx-limited vs. NOx-saturated O
3 production regimes. The results of this analysis will facilitate the development of optimal mitigation policies for O
3 precursor emissions in key agricultural regions around the world. In addition to helping feed a burgeoning global population, higher crop yields resulting from lower ozone concentrations will have the desirable environmental benefit of reducing the amount of additional land that must be brought under cultivation.
We have shown that reducing methane emissions results in global reductions in surface ozone concentrations which has clear benefits to public health. We have also calculated the impact that present and future ozone concentrations have on agriculture in Asia and globally at present and in the next few decades. I wish now to examine the possible global benefits of methane mitigation policies on global agricultural yields as reductions in CH
4 have been shown to reduce surface O
3 concentrations about 1ppb everywhere while generating a significant global climate benefit.
Fast action mitigation strategies
GHG emissions are projected to greatly increase over the next decade and due to political and economic challenges there have been insufficient successful initiatives to slow that rate of growth significantly. In light of this situation, I wish to identify fast action strategies to reduce radiative forcing that can be implemented under existing regulatory authority. Fast action strategies are defined as those which can begin in 2-3 years, be substantially implemented within 5-10 years, and have the goal of producing the desired climate response within decades. Examples of such strategies are: accelerate the phase-out of hydrochlorofluorocarbons (HCFCs), phase down the production of hydrofluorocarbons (HFCs) with high global warming potential, reduce emissions of black carbon (BC) particularly from sources where most of the soot is released in the form of BC rather than organic carbon (OC) and in regions where BC emissions affect snow and ice (eg. Himalaya-Tibetan glaciers, Arctic, etc.), reduce emission of tropospheric ozone (O
3) precursors (particularly methane), enhance biosequestration of carbon, increase surface albedo (eg. white roofs), etc. My goal will be to characterize the benefits of such actions and identify the regulatory pathways by which they may be implemented.
Examine animations of the present and possible future transport of air pollutants from one region of the world to another!