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Chemistry - Climate Connections

We seek to understand factors controlling chemistry-climate interactions including the two-way couplings between air pollutants and climate.  Reducing emissions of some near-term climate forcing agents (NTCFs) such as methane, ozone, and some aerosols offers the potential to address jointly climate and air quality goals.  We study the impacts of climate change on air pollution and the meteorology that drives regional pollutant responses as well as climate responses to changes in NTCFs.

Regional climate responses to aerosol vs.
greenhouse gas forcings

We found that aerosols and greenhouse gases produce similar but opposite signed patterns in extreme temperatures over the United States (see image), leading to large scale cancellations over the historical period ( Mascioli et al., 2016 ).  Extreme precipitation over the eastern United States decreases in response to aerosols, particularly in winter, and increases over the eastern and central United States in response to greenhouse gases, particularly in spring. In the future, aerosol emissions are projected to decrease while greenhouse gas concentrations continue to rise.  As a result, the patterns of extreme temperature and precipitation associated with
greenhouse gas forcing are expected to dominate over the twenty-first century. We found that the U.S. Southeast was less sensitive to climate change than other regions, whether forced by greenhouse gases or aerosols. This finding, along with our interest in reconciling conflicting reports in the literature regarding the U.S. warming hole (a region over the eastern U.S.A. that did not warm over at least some of the 20 th century), led to a systematic examination of observed eastern U.S. temperature trends. Rather than a single ‘warming hole’, we found that different ‘holes’ emerge depending on the season, region, and time period, possibly reflecting different combinations of anthropogenic aerosol forcing and internal climate variability ( Mascioli et al., 2017 ). [EPA]

Climate responses to regional aerosol emission perturbations

This collaborative project sought to identify regional and global climate responses to regional
aerosol emission reductions, separately for sulfate, black carbon, organic carbon, in Asia,
Europe, and the U.S.A., and biomass burning aerosol emissions in South America and Africa.
Using long perturbation simulations (200+ years) relative to a present-day control simulation
(400+ years), we found robust responses in precipitation to regional aerosol emission perturbations: one that corresponds to shifts in the Inter-Tropical Convergence Zone (ITCZ)
positioning over the Sahel, a response attributed previously by climate scientists to global aerosol  forcing, as well as one that is intriguingly ENSO-like (Westervelt et al., 2017; Westervelt et al., 2018). We also investigated regional and global mean and extreme temperature responses (Conley et al., 2018; Westervelt et al., 2020) [NSF EaSM-3]

Future air quality in a changing climate

We have examined changes in surface ozone seasonal cycles under a changing climate (Clifton et al., 2014; Clifton et al., 2020) and in pollution extremes ( Rieder et al., 2015 ; Lin et al., 2017; Rieder et al., 2018) and contributed to reviews of climate change on air quality (Fiore et al., 2012; 2015). Earlier work investigated changes in air pollution meteorology over the northeastern United States including changes in ventilating summertime storms (Turner et al., 2013), in jet latitude, and the implications for surface ozone variability and correlation with temperatures in this region (Barnes and Fiore, 2013). We have also estimated future air pollution and public health burdens under climate and emission scenarios over China (Chen et al., 2018; Westervelt et al., 2019). [EPA, NASA, NOAA, Columbia University]