Abstract
Water-soluble species constitute a significant fraction (up to 60–70%) of the total aerosol loading in the marine atmospheric boundary layer (MABL). The “indirect” effects, that is, climate forcing due to modification of cloud properties depend on the water-soluble composition of aerosols. Thus, the characterization of aerosols over the MABL is of greater relevance. Here, we present 1-year long aerosol chemical composition data of PM10 and PM2.5 at a costal location in the northeastern Arabian Sea (Goa; 15.45°N, 73.20°E, 56 m above the sea level). Average water-soluble ionic concentration (sum of anion and cation) is highest (25.5 ± 6.9 and 19.6 ± 5.8 μg·m−3 for PM10 and PM2.5, respectively) during winter season and lowest during post-monsoon (17.3 ± 9.1 and 14.4 ± 8.1 μg·m−3 for PM10 and PM2.5, respectively). Among water-soluble ionic spices, SO42- ion was found to be dominant species in anions and NH4+ is dominant in cations, for both PM10 and PM2.5 during all the seasons. These observations clearly hint to the contribution from anthropogenic emission and significant secondary inorganic species formation. Sea-salt (calculated based on Na+ and Cl−) concentration shows significant temporal variability with highest contribution during summer seasons in both fractions. Sea-salt corrected Ca2+, an indicator of mineral dust is found mostly during summer months, particularly in PM10 samples, indicates contribution from mineral dust emissions from arid/semiarid regions located in the north/northwestern India and southwest Asia. These observations are corroborated with back-trajectory analyses, wherein air parcels were found to derive from the desert area in summer and Indo-Gangetic Plains (a hot spot for anthropogenic emissions) during winter. In addition, we also observe the presence of nss-K+ (sea-salt corrected), for PM2.5, particularly during winter months, indicating influence of biomass burning emissions. The impact on aerosol chemistry is further assessed based on chloride depletion. Chloride depletion is observed very significant during post-monsoon months (October and November), wherein more than 80 up to 100% depletion is found, mediated by excess sulfates highlighting the role of secondary species in atmospheric chemistry. Regional scale characterization of atmospheric aerosols is important for their better parameterization in chemical transport model and estimation of radiative forcing.
Highlights
Atmospheric aerosols, derived from continental regions, undergo long-range transport and supply significant amount of nutrients as well as toxicants to remote and coastal oceanic region (Jickells et al, 2005; Paytan et al, 2009; Kumar et al, 2010; Jordi et al, 2012; Baker et al, 2013; Srinivas and Sarin, 2013a; Powell et al, 2015; Kumar et al, 2020)
Winds during WIN season are mostly derived from continental locations in the Indian subcontinent, from the Indo-Gangetic Plains
We present here a one-year long aerosol chemical composition data of size-segregated aerosols (PM10 and PM2.5) at a costal location in the northeastern Arabian Sea (Goa; 15.45°N, 73.20°E, 56 m above the sea level)
Summary
Atmospheric aerosols, derived from continental regions, undergo long-range transport and supply significant amount of nutrients as well as toxicants to remote and coastal oceanic region (Jickells et al, 2005; Paytan et al, 2009; Kumar et al, 2010; Jordi et al, 2012; Baker et al, 2013; Srinivas and Sarin, 2013a; Powell et al, 2015; Kumar et al, 2020). The availability (and lability) of nutrients/toxicants significantly depend on the ambient atmospheric chemistry (Baker and Croot, 2010; Kumar and Sarin, 2010a), which eventually undergo dry (Arimoto et al, 2003; Srinivas and Sarin, 2013a; Baker et al, 2017) as well as wet (Measures and Vink, 1999; Chance et al, 2015; Powell et al, 2015) deposition. Considering the importance of chemical composition, efforts have been made in the past to chemically characterize aerosols over continental (Wang and Shooter, 2001; Tare et al, 2006; Williams et al, 2007; Ng et al, 2011; Sahai et al, 2011; Sun et al, 2012; Jain et al, 2014; Tiwari et al, 2014; Petit et al, 2015) as well as marine regions (Siefert et al, 1999; Johansen and Hoffmann, 2003; Kumar et al, 2008a; Kumar et al, 2008b; van Pinxteren et al, 2015; Budhavant et al, 2017; Pan et al, 2018; Aswini et al, 2020a; Cvitesic Kusan et al, 2020)
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