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Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere.

ABSTRACT: We implement oceanic dimethylsulfide (DMS) emissions and its atmospheric chemical reactions into the Community Multiscale Air Quality (CMAQv53) model and perform annual simulations without and with DMS chemistry to quantify its impact on tropospheric composition and air quality over the Northern Hemisphere. DMS chemistry enhances both sulfur dioxide (SO₂) and sulfate ( SO42- ) over seawater and coastal areas. It enhances annual mean surface SO₂ concentration by +46 pptv and SO42- by +0.33 μg/m³ and decreases aerosol nitrate concentration by -0.07 μg/m³ over seawater compared to the simulation without DMS chemistry. The changes decrease with altitude and are limited to the lower atmosphere. Impacts of DMS chemistry on SO42- are largest in the summer and lowest in the fall due to the seasonality of DMS emissions, atmospheric photochemistry and resultant oxidant levels. Hydroxyl and nitrate radical-initiated pathways oxidize 75% of the DMS while halogen-initiated pathways oxidize 25%. DMS chemistry leads to more acidic particles over seawater by decreasing aerosol pH. Increased SO42- from DMS enhances atmospheric extinction while lower aerosol nitrate reduces the extinction so that the net effect of DMS chemistry on visibility tends to remain unchanged over most of the seawater.

SUBMITTER: Zhao J

PROVIDER: S-EPMC7592702 | biostudies-literature | 2020 Oct

REPOSITORIES: biostudies-literature

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Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere.

Zhao Junri J Sarwar Golam G Gantt Brett B Foley Kristen K Henderson Barron H BH Pye Havala O T HOT Fahey Kathleen K Kang Daiwen D Mathur Rohit R Zhang Yan Y Li Qinyi Q Saiz-Lopez Alfonso A

Atmospheric environment (Oxford, England : 1994) 20201001

We implement oceanic dimethylsulfide (DMS) emissions and its atmospheric chemical reactions into the Community Multiscale Air Quality (CMAQv53) model and perform annual simulations without and with DMS chemistry to quantify its impact on tropospheric composition and air quality over the Northern Hemisphere. DMS chemistry enhances both sulfur dioxide (SO<sub>2</sub>) and sulfate ( SO42- ) over seawater and coastal areas. It enhances annual mean surface SO<sub>2</sub> concentration by +46 pptv and ...[more]

PMID: 33132736

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Project description:We use the Community Multiscale Air Quality (CMAQv5.4) model to examine the potential impact of particulate nitrate (pNO3-) photolysis on air quality over the Northern Hemisphere. We estimate the photolysis frequency of pNO3- by scaling the photolysis frequency of nitric acid (HNO3) with an enhancement factor that varies between 10 and 100 depending on pNO3- and sea-salt aerosol concentrations and then perform CMAQ simulations without and with pNO3- photolysis to quantify the range of impacts on tropospheric composition. The photolysis of pNO3- produces gaseous nitrous acid (HONO) and nitrogen dioxide (NO2) over seawater thereby increasing atmospheric HONO and NO2 mixing ratios. HONO subsequently undergoes photolysis, producing hydroxyl radicals (OH). The increase in NO2 and OH alters atmospheric chemistry and enhances the atmospheric ozone (O3) mixing ratio over seawater, which is subsequently transported to downwind continental regions. Seasonal mean model O3 vertical column densities without pNO3- photolysis are lower than the Ozone Monitoring Instrument (OMI) retrievals, while the column densities with the pNO3- photolysis agree better with the OMI retrievals of tropospheric O3 burden. We compare model O3 mixing ratios with available surface observed data from the U.S., Japan, the Tropospheric Ozone Assessment Report - Phase II, and OpenAQ; and find that the model without pNO3- photolysis underestimates the observed data in winter and spring seasons and the model with pNO3- photolysis improves the comparison in both seasons, largely rectifying the pronounced underestimation in spring. Compared to measurements from the western U.S., model O3 mixing ratios with pNO3- photolysis agree better with observed data in all months due to the persistent underestimation of O3 without pNO3- photolysis. Compared to the ozonesonde measurements, model O3 mixing ratios with pNO3- photolysis also agree better with observed data than the model O3 without pNO3- photolysis.

Dataset Information

Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere.

Publications

Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere.

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