Objective: Improved predictive capability through a better understanding of the connections between emissions, atmospheric composition, and Earth's climate system.
CSD Climate Research is focused on (1) short-lived climate pollutants (SLCPs); and (2) addressing water vapor and aerosols (airborne fine particles) – two of the greatest uncertainties in current climate models. This is done through understanding and quantifying various chemical and dynamical processes that influence climate.
Short-lived climate pollutants (SLCPs) include methane, tropospheric ozone, aerosols (including black carbon), and substitutes for ozone-depleting substances (including hydrofluorocarbons, HFCs). They contribute directly to climate forcing, are key to many climate feedbacks, link climate change and air quality, and are areas of current focus for policy formulation. The IPCC has identified the role of atmospheric aerosols in climate change as the single greatest uncertainty in our ability to predict changes to the climate system. This role includes physical and chemical processes by which aerosols influence clouds, as well as various cloud properties.
Research at CSD is addressing key uncertainties related to: (1) tropospheric ozone, (2) aerosols (both absorbing, e.g., black carbon, that warm the Earth's atmosphere and scattering, e.g., sulfate aerosols, that cool the surface), (3) emissions of chemically active greenhouse gases such as methane and nitrous oxide, and (4) quantifying the influence of aerosols on cloud formation, extent, and optical properties (Earth's radiation balance) as well as on precipitation. This research integrates laboratory, field, and modeling work to understand processes related to chemistry and transport. Central to this work is the development of instruments that are sensitive and selective for "difficult-to-measure," but important, atmospheric gases and particles. A particular focus is on quantification of emissions of precursors for ozone and aerosols, as well as of key chemically active greenhouse gases, such as nitrous oxide and methane.
The water vapor abundance in the upper troposphere and lower stratosphere (UT/LS) is a critical factor in determining the amount of radiation lost to space and thus determining the energy budget of Earth's surface. Water vapor in this region, though, is particularly difficult to quantify. A better quantification of water vapor and its distribution in this part of the atmosphere is needed to properly account for past changes in the Earth's climate and reliably predict/project future changes. Work is underway in CSD to improve the measurement of water vapor in the UT/LS and enhance the understanding of its atmospheric distribution.
CSD makes ongoing contributions to (1) advancing scientific knowledge regarding the processes involved in ozone-layer depletion by chlorofluorocarbons and other compounds, (2) assessments of the state of knowledge regarding stratospheric ozone, and (3) communication of that information to policymakers in formats that are useful to their decision-making process. CSD is a lead participant in scientific state-of-understanding assessment reports for decision-makers, and has been since the inception of the United Nations Montreal Protocol, the 1987 international agreement that protects the ozone layer. U.S. policy makers, the U.S. chemical industry, EPA, and other national and international agencies rely on these scientific assessments as a basis for their development of scientifically sound, well-informed policies.
Objective: Provide sound science to support informed air-quality decision-making at national, state, and local levels.
Air quality research on (i) improving understanding of the processes responsible for poor air quality, i.e., surface ozone and particulate matter suspended in air (PM, also referred to as aerosols), and (ii) enhancing predictive capability is essential for air quality management and forecast applications. There is also a strong demand for working with stakeholders to identify their needs up front, and then communicating research results to air quality decision-makers in a timely, user-friendly manner.
Many atmospheric constituents, both natural and manmade, interact to affect surface ozone and PM levels. In addition, the factors that influence air quality differ at the regional scale across the U.S. CSD research is focused on key regions of the U.S. that are impacted by poor air quality. The aim of the research is to understand the sources of these constituents and the nature of their interactions, in order to provide a basis for determining how to mitigate the problem of surface ozone and PM pollution. CSD scientists also focus on understanding the precursors, chemical processes, and boundary layer meteorology that influence the formation of atmospheric aerosols. As air quality regulatory standards tighten, regional to intercontinental transport of pollution, as well as stratospheric intrusions of ozone, become critical issues for attainment of those standards. Moreover, national policy, such as the quest for energy independence via oil and natural gas development, can have a significant impact on regional and local air quality issues. CSD research is addressing these emerging air quality issues through laboratory studies, instrument development activities, biennial intensive field studies coupled with model analysis, and providing the information to users.
Objective: Linking emissions to impacts – climate and air quality.
The three major environmental issues of climate change, air quality, and stratospheric changes are interlinked in science and in policy. Research is needed to advance scientific understanding at the intersections of these issues.
The interplay between air quality and climate change with regard to the short-lived climate pollutants (SLCPs) is a major research theme. Emissions of SLCPs and their precursors are one of the most uncertain components in understanding, attributing, and predicting climate change and its interactions with other impacts, in particular air quality. A key example is tropospheric ozone. Emissions from anthropogenic activities have made ozone a regional air quality problem, but increases in tropospheric ozone have also exacerbated climate forcing. Many air quality regulatory actions are already codified and their implementation will have impacts on climate – some negative, some positive, and some neutral. One of the main issues in climate change mitigation efforts is to manage emissions (one of the few knobs a society can turn!) for the benefit of multiple issues, but also to avoid unintended consequences. For example, current agricultural practices require intensive application of nitrogen-based fertilizers to increase crop yields. This has the potential to affect (1) air quality through soil emissions of nitrogen oxides (NOx), (2) climate change via soil emission of the potent greenhouse gas nitrous oxide (N2O), and (3) stratospheric ozone, again via soil emission of N2O.
There is evidence that stratospheric changes affect climate or might be affected by climate. The connection between the recovery of the stratospheric ozone layer and climate is a prime example. Other examples include connections between stratospheric water vapor and surface temperature changes, and changes in stratospheric circulation that influence, and are influenced by, climate change.
CSD is working to provide scientific information that helps identify options for air quality management that will also benefit climate change mitigation and for climate policy issues that influence air quality. Similarly, CSD also addresses issues such as the role of stratospheric intrusions on surface ozone, role of transport from other continents on surface ozone, etc. A major example of how CSD implements this research is our field missions, augmented by laboratory studies and modeling analyses, which are designed to address both air quality and climate objectives. The thrust is to provide science-based information to decision-makers. CSD achieves these objectives through research and communicating the information in a usable form to decision-makers.