10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Compositional Analysis of Aerosols and Rain Water during Weak South-west Monsoon Period
PRADHI RAJEEV, Prashant Rajput, Gyanesh Kumar Singh, Vikram Choudhary, Amit Kumar Singh, Tarun Gupta, Indian Institute of Technology Kanpur
Abstract Number: 344 Working Group: Aerosol Chemistry
Abstract Particulate matter (PM) loading during South-west (SW) monsoon is significantly less over the Indo-Gangetic Plain (IGP) due to frequent wash out by wet precipitation and high convective mixing [Temp: ~ 40 °C; wind speed: ~8 m/s]. However in year 2015, weak SW-monsoon due to El-Niño and positive phase of Pacific Decadal Oscillation (PDO) has resulted in less rainfall (~ 375 mm) than usual (~ 900 mm) over the IGP region. Thus, low wet precipitation has facilitated to assess several characteristic features of aerosols and rain waters during the SW-monsoon. We have conducted a study in the central IGP during SW-monsoon to assess chemical characteristics of ambient atmospheric aerosols (PM2.5; n= 42; 42.2 ± 22.4 µg/m3) and individual rain water samples (pH: 6.4−7.6; n = 15). Different chemical constituents like organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), water-soluble inorganic species (WSIS), water-soluble total nitrogen (WSTN) and metals have been studied in aerosols. However, in rain water samples, pH, electrical conductivity, WSOC, WSIS and WSTN have been assessed. In aerosol samples, the contribution of secondary inorganic species viz. SO42-, NH4+ and NO3- in WSIS were found to be predominant. In a sharp contrast, HCO3- and Ca2+ constituted the major fraction of total WSIS in rain waters. Characteristic mass ratios among ionic species in rain waters and aerosol samples suggest that below-cloud scavenging is predominant mechanism of aerosols wash out over the region. The mass contribution of total carbonaceous aerosols (TCA), mineral dust (MD) and WSIS in PM2.5 was found to be 22%, 37% and 35%, respectively. Higher contribution of mineral dust in PM2.5 is attributable to significant upliftment of mineral aerosols due to drier weather condition and high wind speed. Mineral dust characteristics in PM2.5 have been assessed systematically utilizing elemental ratios of major crustal metals i.e. Fe/Al, Ca/Al and Mg/Al. Our study documents that rain waters over the IGP is alkaline in nature and provides a field-based evidence that fine fraction mineral dust favors the uptake of secondary species like nitrate.