Citation:

Itahashi, S., R. Mathur, C. Hogrefe, S. Napelenok, AND Y. Zhang. Incorporation of volcanic SO2 emissions in the Hemispheric CMAQ (H-CMAQ) version 5.2 modeling system and assessing their impacts on sulfate aerosol over the Northern Hemisphere. Geoscientific Model Development . Copernicus Publications, Katlenburg-Lindau, Germany, 14(9):5751–5768, (2021). https://doi.org/10.5194/gmd-14-5751-2021

Impact/Purpose:

As SO2 emission control is reducing regional airborne SO42-, quantifying the relative contribution of long-range transported SO42- and the portion attributable to natural sources is becoming increasingly important. For instance, regional haze assessments require more accurate quantification of visibility impairment that are associated with anthropogenic enhancements over natural visibility levels, which in turn necessitates accurate quantification of the contribution of natural sources. Next to the anthropogenic emissions, volcanic emissions have an important contribution to SO2 emissions and potentially influence the composition and amounts of particulate matter transported into a region. This study assess the impacts of volcanic degassing emissions on tropospheric sulfate aerosol budgets. Results from analysis of detailed model calculations indicate that the degassing volcanic SO2 emissions are an important source impacting airborne sulfur budgets and should be considered in air quality model simulations assessing background sulfate and PM2.5 levels and their source attribution.

Description:

The state-of-the-science Community Multiscale Air Quality (CMAQ) Modeling System has recently been extended for hemispheric-scale modeling applications (referred to as H-CMAQ). In this study, satellite-constrained estimation of the degassing SO2 emissions from 50 volcanos over the northern hemisphere is incorporated into H-CMAQ, and their impact on tropospheric sulfate aerosol (SO42-) levels is assessed for 2010. The volcanic degassing improves predictions of observations from the Acid Deposition Monitoring Network in East Asia (EANET), the United States Clean Air Status and Trends Network (CASTNET), and the United States Integrated Monitoring of Protected Visual Environments (IMPROVE). Over Asia, the increased SO42- concentrations were seen to correspond to the locations of volcanoes, especially over Japan and Indonesia. Over the U.S.A., the largest impacts occurred over the central Pacific caused by including the Hawaiian Kilauea volcano while the impacts on the continental U.S.A. were limited to the western portion during summertime. The emissions of the Soufriere Hills volcano located on Montserrat Island in the Caribbean Ocean affected the southeastern U.S.A. during the winter season. The analysis at specific sites in Hawaii and Florida also confirmed improvements in regional performance for modeled SO42- by including volcanoes SO2 emissions. At the edge of the western U.S.A., monthly-averaged SO42- enhancements greater than 0.1 μg/m3 were noted within the boundary layer (defined as surface to 750 hPa) during June-September. Investigating the change on SO42- concentration throughout the free troposphere revealed that although the considered volcanic SO2 emissions occurred at or below the middle of free troposphere (500 hPa), influences more than 10% on relative percentages compared to the simulation without volcano source were detected up to the top of the free troposphere (250 hPa). Our model simulations and comparisons with measurements across the Northern Hemisphere indicate that the degassing volcanic SO2 emissions are an important source impacting airborne sulfur budgets and should be considered in air quality model simulations assessing background sulfate levels and their source attribution.

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