Study of chemical species associated with fine particles and their secondary particle formation at semi-arid region of India

Özet

The fine particles (PM2.5) were collected for 24 h from Agra atmosphere and chemically characterized during the one year study period. The average concentration of PM2.5 was 90.21 ± 20.62 mg m3 which is higher than NAAQS and WHO annual standards and their seasonal trend was winter > summer > monsoon. Ionic study indicates that cations were dominant in comparison to anions. Seasonally, F, Ca2þ and Mg2þ were higher during summer period and Cl, NO 3 , NHþ 4 and Kþ were higher during monsoon period while SO2 4 was higher during winter season. The ratios Ca2þ/Naþ, Mg2þ/Naþ and SO2 4 /Naþ were higher, while Cl/Na ratio was lower than sea water ratio indicating the incorporation of non marine constituents in aerosols. The observed Cl/Naþ (average 0.71) deviate considerable from the Sea water ratio suggesting either a fractionation of Cl or enrichment of Naþ as there was significant deviation from marine sources. Linear correlation was observable between nss-Ca2þ and nss-Mg2þ with HCO3 throughout the annual seasonal cycle (HCO3 : Ca ¼ 0.59, HCO3 : Mg2þ ¼ 0.53) suggesting the origination of these species from soil dust. The calculated conversion ratio of ‘S’ (CRS) was lower than ‘N’ (CRN) which suggests that the secondary formation of NO 3 aerosol from NO2 was more predominant than SO2 4 . Trajectory analysis indicates that long range transportation also contributes to PM2.5 mass over the measurement site.