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Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
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Particulate air pollution in the atmosphere can impact the availability of gas-phase chemical constituents, which can then have feedbacks on gas-phase air pollutants. We use a chemistry-climate computer model to simulate the impact of particulate pollution from three major world regions on gas-phase chemical constituents. We find that surface level ozone air pollution decreases by up to 5 ppbv over China in response to Chinese particulate air pollution, which has implications for policy.
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https://doi.org/10.5194/acp-2020-1255
https://doi.org/10.5194/acp-2020-1255

  05 Jan 2021

05 Jan 2021

Review status: this preprint is currently under review for the journal ACP.

Impact of northern hemisphere mid-latitude anthropogenic sulfur dioxide emissions on local and remote tropospheric oxidants

Daniel M. Westervelt1,2, Arlene M. Fiore1,3, Colleen B. Baublitz1,3, and Gustavo Correa1 Daniel M. Westervelt et al.
  • 1Lamont-Doherty Earth Observatory, Columbia University. Palisades, New York, USA
  • 2NASA Goddard Institute for Space Studies, New York, New York, USA
  • 3Department of Earth and Environmental Sciences, Columbia University, Palisades, New York, USA

Abstract. The unintended consequences of reductions in regional anthropogenic sulfur dioxide (SO2) emissions implemented to protect human health are poorly understood. SO2 decreases began in the 1970s in the US and Europe and are expected to continue into the future, while recent emissions decreases in China are also projected to continue. In addition to the well documented climate effects (warming) from reducing aerosols, tropospheric oxidation is impacted via aerosol modification of photolysis rates and radical sinks. Impacts on the hydroxyl radical and other trace constituents directly affect climate and air quality metrics such as surface ozone levels. We use the Geophysical Fluid Dynamics Laboratory Atmospheric Model version 3 nudged towards National Centers for Environmental Prediction (NCEP) reanalysis wind velocities to estimate the impact of SO2 emissions from the United States, Europe, and China by differencing a control simulation with an otherwise identical simulation in which 2015 anthropogenic SO2 emissions are set to zero over one of the regions. Springtime sulfate aerosol changes occur both locally to the emission region and also throughout the Northern Hemispheric troposphere, including remote oceanic regions and the Arctic. The presence of sulfate aerosol strongly reduces hydroxyl (OH) and hydroperoxy (HO2) radicals by up to 10 % year-round throughout most of the troposphere north of 30° N latitude, the latter of which is directly removed via heterogeneous chemistry on aerosol surfaces, including sulfate, in the model. Regional SO2 emissions significantly increase nitrogen oxides (NOx) by about 5–8 % throughout most of the free troposphere in the Northern hemisphere by increasing the NOx lifetime as the heterogeneous sink on sulfate aerosol declines. Despite the NOx increases, tropospheric ozone decreases at northern mid-latitudes by 1–4 % zonally averaged and by up to 5 ppbv in surface air over China, as its response is dominated by the larger decreases (up to 2x) in HO2 and OH. Since 2015 anthropogenic SO2 emissions in China exceed those in the US or Europe, the oxidative response is greatest for the China perturbation simulation. Chemical effects of aerosols on oxidation (reactive uptake) dominate over radiative effects (photolysis rates), the latter of which are only statistically significant locally for the large perturbation over China. We find that the emissions decrease in China, which has yet to be fully realized, will have the largest impact on oxidants and related species in the Northern Hemisphere free troposphere compared to changes in Europe or the USA. Our results bolster previous calls for a multipollutant strategy for air pollution mitigation, to avoid the unintended consequence of aerosol removal leading to surface ozone increases that offset or mask surface ozone gains achieved by regulation of other pollutants, especially in countries where current usage of high-sulfur emitting fuels may be phased out in the future.

Daniel M. Westervelt et al.

Status: open (until 02 Mar 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Daniel M. Westervelt et al.

Daniel M. Westervelt et al.

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Short summary
Particulate air pollution in the atmosphere can impact the availability of gas-phase chemical constituents, which can then have feedbacks on gas-phase air pollutants. We use a chemistry-climate computer model to simulate the impact of particulate pollution from three major world regions on gas-phase chemical constituents. We find that surface level ozone air pollution decreases by up to 5 ppbv over China in response to Chinese particulate air pollution, which has implications for policy.
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