PAOC Special Seminar - Jareth Holt, MIT

"Sensitivity of Air Quality and Climate Impacts of Inorganic Aerosols to US Precursor Emissions" | Fine particulate matter affects both air quality and radiative balance. Inorganic particulates, made of sulfate, nitrate, and ammonium, form in the atmosphere from precursor emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and ammonia (NH3). Between 2005 and 2012, US SO2 and NOx emissions have decreased by 62% and 42% potentially large enough for a nonlinear response. I will discuss chemical transport model simulations that we used to estimate how sensitivities of both air quality and climate metrics to emissions have changed. In winter, much of the central US transitioned from NH3-limited to NH3-saturated, increasing the sensitivity to NOx emissions. In summer, lower NOx leads to higher H2O2 concentrations; faster aqueous SO2 oxidation; and an increased sensitivity to SO2 emissions. Aerosol nitrate forms in the mid-troposphere in both seasons under low emissions, contributing much more to aerosol radiative effects than under low emissions. As emissions continue to change, representing the nonlinear response to NOx emissions will be necessary for accurate air quality and near-term climate forecasting.

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