Science Inventory

Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere

Citation:

Gantt, B., K. Foley, B. Henderson, H. Pye, K. Fahey, D. Kang, R. Mathur, J. Zhao, Y. Zhang, Q. Li, A. Saiz-Lopez, AND G. Sarwar. Impact of dimethylsulfide chemistry on air quality over the Northern Hemisphere. ATMOSPHERIC ENVIRONMENT. Elsevier Science Ltd, New York, NY, 244:117961, (2020). https://doi.org/10.1016/j.atmosenv.2020.117961

Impact/Purpose:

Biogenic emission of dimethyl sulfide (DMS) from oceanic is the major natural source of sulfur into the atmosphere. In this study, 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. The model without the DMS chemistry predicts low concentrations of sulfur dioxide (SO2) and sulfate (SO_4^(2-)) over seawater. DMS chemistry enhances both SO2 and SO_4^(2-)over seawater and coastal areas. It enhances annual mean surface SO2 concentration by ~90% and SO_4^(2-) concentration by ~30% over the entire seawater compared to simulation without the DMS chemistry. The enhancements decrease with altitude and are limited to the lower atmosphere. The impact of DMS chemistry on SO_4^(2-) is the largest in the summer and lowest in the fall due to the seasonality in DMS emissions, atmospheric photochemistry and resultant oxidant levels. Oceanic DMS enhances annual average SO2 by 6 pptv and SO_4^(2-) by 0.09 μg/m3 across the entire U.S. The hydroxyl and nitrate radical-initiated pathways oxidize 75% of the DMS while the halogens-initiated pathways oxidize 25%. DMS chemistry decreases aerosol pH and atmospheric visibility over seawater and coastal areas due to the enhancement of SO_4^(2-). DMS chemistry generally captures the observed methanesulfonic acid to non-sea-salt SO_4^(2-)(nss-SO_4^(2-)) ratio.

Description:

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. The model without the DMS chemistry predicts low concentrations of sulfur dioxide (SO2) and sulfate (SO_4^(2-)) over seawater. DMS chemistry enhances both SO2 and SO_4^(2-)over seawater and coastal areas. It enhances annual mean surface SO2 concentration by ~90% and SO_4^(2-) concentration by ~30% over the entire seawater compared to simulation without the DMS chemistry. The enhancements decrease with altitude and are limited to the lower atmosphere. The impact of DMS chemistry on SO_4^(2-) is the largest in the summer and lowest in the fall due to the seasonality in DMS emissions, atmospheric photochemistry and resultant oxidant levels. Oceanic DMS enhances annual average SO2 by 6 pptv and SO_4^(2-) by 0.09 μg/m3 across the entire U.S. The hydroxyl and nitrate radical-initiated pathways oxidize 75% of the DMS while the halogens-initiated pathways oxidize 25%. DMS chemistry decreases aerosol pH and atmospheric visibility over seawater and coastal areas due to the enhancement of SO_4^(2-). DMS chemistry generally captures the observed methanesulfonic acid to non-sea-salt SO_4^(2-)(nss-SO_4^(2-)) ratio.