Air Quality & Climate

Climate and air quality are two imminent areas of environmental sciences, and they are associated closely through numerous complex physical and chemical processes. Air quality in New England is especially susceptible to variations in seasonal climate due to its extensive areal forest coverage, complex terrain features, and significant influx of air pollutants from major urban/industrial centers in the eastern U.S. There is already strong evidence that the length of the growing season is increasing in New England. Longer and hotter summers should not only have a major impact on biogenic emissions, but also on air quality and the occurrence of O₃ episodes. To provide an assessment of the quality of our present environment, it is imperative to identify the key mechanisms that control these processes to better understand the variability in climate and levels of persistent pollutants such as O₃ and Hg°.

Dynamical processes on different spatial and temporal scales together shape air quality in New England. Atmospheric chemical composition at mid–latitudes can be altered by interannual variability in large–scale circulation patterns. For example, our recent studies found that the enhanced mixing ratios of O₃ in winter 2003, compared to winter 2002, was the result of strong meridional flows transporting abnormally cold and O₃–rich air masses from the Arctic troposphere to the northeastern U.S. In addition, synoptic southwesterly flow in summer can transport high levels of pollutants including O3 from metropolitan areas in southern New England or even as far south as the Mid–Atlantic States. On a smaller scale, interdiurnal variability in atmospheric processes, such as the evolution of Canadian low pressure system and day–to–day migration of high pressure over the North Atlantic Ocean, is non–periodic, which is key to the occurrence of air pollution episodes and generation of outflow from North American Conceivably interdiurnal, intraseasonal, and interannual variability in meso– to hemispheric– scale dynamic processes have a profound impact on atmospheric chemistry in the northeast.

Natural ecosystems are sensitive to climate change, and the resulting perturbation in vegetation will inevitably influence the exchange of trace gases (e.g., biogenic volatile organic compounds—BVOC’s) between soil, vegetation, and the atmosphere. As a result, year–to–year changes in climate variables such as temperature, moisture, and radiation during the growing season can influence BVOC emissions with subsequent effects on O₃ photochemistry. It is thus critical to quantify climate change in the northeastern U.S. and its impact on biogenic emissions and subsequently O₃ and its precursors. Such interdisciplinary research not only provides a quantitative assessment of present day climate and air quality, but establishes a solid foundation for estimating future changes.