Aeolian Dust and Sea Salt in Marine Aerosols over the Arabian Sea during the Southwest Monsoon: Sources and Spatial Variability

Abstract

The nutrient supply to the oceanic surface water is largely regulated by the extrinsic and intrinsic ambient atmospheric aerosol properties, particularly chemistry. In this context, we measured the comprehensive chemical composition (inorganic ions and major elements) of atmospheric aerosols and studied their spatial distribution over the Arabian Sea during the southwest monsoon (SWM) period for 2 consecutive years (2017 and 2018). We found that the water-soluble ionic concentration (WSIC) is dominated by Na+ and Cl– ions followed by Ca2+ and SO4 2– with a minor contribution of Mg2+ and NO3 –. The relative contribution of ionic species to WSIC remained similar for both the monsoon seasons with higher WSIC during 2018 (69.3 ± 63 μg m–3) compared to 2017 (40.6 ± 33 μg m–3). Sea salt (estimated from Na+ and Cl– ions) and mineral dust (calculated from the Al concentration) are dominant constituents of aerosols, with negligible contribution from anthropogenic species found to be temporally and spatially consistent during both the campaigns. The mineral dust is characterized by a uniform Nd isotopic signature during both campaigns, indicating its source to the Arabian Peninsula during the study period. Source apportionment of mineral dust using the Nd isotope is supported by back-trajectory analyses as well as satellite retrieved (MODIS and CALIPSO) data. The Cl– deficit, which is mainly attributed to the interaction of sea salt with acidic species, is found to be relatively low (10–12%) compared to that during continental outflow over the Arabian Sea, indicating the insignificant contribution from anthropogenic emissions during the SWM months.

Bioactive Trace Elements’ Composition and Their Fractional Solubility in Aerosols from the Arabian Sea during the Southwest Monsoon

“…A 10 mL aliquot of extracted leachate was acidified for water-soluble TE analyses, and another aliquot was stored in a deep freezer (−20 °C) till its analysis for cations and anions. Details of analyses of cation and anion using ion chromatography can be found in Aswini et al…”

“…This region experiences a seasonal reversal of wind due to the monsoon system; thus, the calculated annual DF will have large uncertainty. Considering this, we have estimated the seasonal average DF using V d = 1 cm s –1 for crustal elements (Fe and Mn) associated with coarser dust; however, for Cu, we used V d = 0.3 m s –1 , considering its association with a finer anthropogenic fraction. , In previous studies, Srinivas and Sarin, as well as Pryor and Sørensen, have reported that an increase in wind speed can increase the sub-micron size particle, which is prevalant in the ARS during monsoon months as compared to other seasons …”

“…A 10 mL aliquot of extracted leachate was acidified for water-soluble TE analyses, and another aliquot was stored in a deep freezer (−20 °C) till its analysis for cations and anions. Details of analyses of cation and anion using ion chromatography can be found in Aswini et al 20 For total metal analysis, filters were cut and transferred to acid precleaned 15 mL Savillex vials along with a 7 mL mixture of suprapure acids (HF and HNO 3 in 2:5 ratio). Post transfer, all vials were kept on a hot plate at 110 °C for 24 h. Subsequently, samples were dried, 2 mL of suprapure concentrated HNO 3 was added, and open digestion was performed on the hot plate.…”

“…14,26 In previous studies, Srinivas and Sarin, 34 as well as Pryor and Sørensen, 59 have reported that an increase in wind speed can increase the sub-micron size particle, which is prevalant in the ARS during monsoon months as compared to other seasons. 20 2.5. Enrichment Factor.…”

Impact of atmospheric anthropogenic nitrogen on new production in the northern Indian Ocean: constrained based on satellite aerosol optical depth and particulate nitrogen levels

“…8,[34][35][36] In addition, efforts have been made to measure the chemical composition of aerosols under the aegis of several national and international programs in India. 13,14,19,23,25,32,[37][38][39][40] Combining several snapshot measurements, Srinivas and Sarin 38 estimated that dry deposition of inorganic nutrients supports $13% of the surface primary production in the Bay of Bengal (BoB) and $5% of the surface primary production in the Arabian Sea (AS) during the dry period. Similarly, Yadav et al 32 highlighted that $70% of the total suspended particulate matter (TSP) was deposited within 10 km from the coast and can support 3 to 33% of the coastal surface primary production during fall and winter seasons in the BoB.…”