Abstract
Abstract. 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 volcanoes 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 USA, the largest impacts that occurred over the central Pacific were caused by including the Hawaiian Kilauea volcano, while the impacts on the continental USA were limited to the western portion during summertime. The emissions of the Soufrière Hills volcano located on the island of Montserrat in the Caribbean Sea affected the southeastern USA 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 USA, monthly averaged SO42- enhancements greater than 0.1 µg m−3 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), compared to the simulation without the volcanic source, SO42- enhancements of more than 10 % 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 and should be considered in air quality model simulations assessing background SO42- levels and their source attribution.
Highlights
Airborne sulfate (SO24−) is one of the major components of tropospheric particulate matter worldwide (Zhang et al, 2007) and plays important roles in modulating the earth– atmosphere energy budget, atmospheric circulation, cloud properties, and precipitation (Seinfeld and Pandis, 2016)
The annual averaged SO24− simulated after incorporating degassing volcanic SO2 emission in H-Community Multiscale Air Quality (CMAQ) is shown in Fig. 3b, and the increase in concentrations relative to the base H-CMAQ is shown in Fig. 3c as absolute value and in Fig. 3d as the percentage change from the original HCMAQ simulation
The improvements were noticeable in the comparison with observations at Integrated Monitoring of Protected Visual Environments (IMPROVE) sites located in the western USA; normalized mean bias (NMB) showed close agreement between H-CMAQ and IMPROVE observation
Summary
Airborne sulfate (SO24−) is one of the major components of tropospheric particulate matter worldwide (Zhang et al, 2007) and plays important roles in modulating the earth– atmosphere energy budget, atmospheric circulation, cloud properties, and precipitation (Seinfeld and Pandis, 2016). Anthropogenic SO2 emissions across Asia, especially China, have shown a continuous increase since 1970 (Smith et al, 2011) up to 2006 and decreased (Li et al, 2017) in response to control measures These multi-decadal changes in SO2 emissions have resulted in contrasting changes in tropospheric SO24− levels and in aerosol radiative effects (e.g., Wild et al, 2009; Xing et al, 2015b), their feedback on atmospheric dynamics and air quality (e.g., Xing et al, 2016), and acid deposition (e.g., Zhang et al, 2018; Mathur et al, 2020). Since anthropogenic SO2 emissions have changed significantly over the past several decades, and since recent studies provide improved constraints of volcanic SO2 emissions, the work summarized in this article attempts to assess the contributions of volcanic SO2 emissions on tropospheric SO42− distributions across the Northern Hemisphere and North America. Marizes the key results and limitations of this work and discusses future perspectives
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