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Aerosol characteristics during winter fog at Agra, North India

Safai, PD and Kewat, S and Pandithurai, G and Praveen, PS and Ali, K and Tiwari, S and Rao, PSP and Budhawant, KB and Saha, SK and Devara, PCS (2008) Aerosol characteristics during winter fog at Agra, North India. Journal of Atmospheric Chemistry, 61 (2). pp. 101-118.

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Simultaneous measurements on physical, chemical and optical properties of aerosols over a tropical semi-arid location, Agra in north India, were undertaken during December 2004. The average concentration of total suspended particulates (TSP) increased by about 1.4 times during intense foggy/hazy days. Concentrations of SO4 2-, NO3 -, NH4 + and Black Carbon (BC) aerosols increased by 4, 2, 3.5 and 1.7 times, respectively during that period. Aerosols were acidic during intense foggy/hazy days but the fog water showed alkaline nature, mainly due to the neutralizing capacity of NH4 aerosols. Trajectory analyses showed that air masses were predominantly from NW direction, which might be responsible for transport of BC from distant and surrounding local sources. Diurnal variation of BC on all days showed a morning and an evening peak that were related to domestic cooking and vehicular emissions, apart from boundary layer changes. OPAC (Optical properties of aerosols and clouds) model was used to compute the optical properties of aerosols. Both OPAC-derived and observed aerosol optical depth (AOD) values showed spectral variation with high loadings in the short wavelengths (<1 μm). AOD value at 0.5 μm wavelength was significantly high during intense foggy/hazy days (1.22) than during clear sky or less foggy/hazy days (0.63). OPAC-derived Single scattering albedo (SSA) was 0.84 during the observational period, indicating significant contribution of absorbing aerosols. However, the BC mass fraction to TSP increased by only 1 during intense foggy/hazy days and thereby did not show any impact on SSA during that period. A large increase was observed in the shortwave (SW) atmospheric (ATM) forcing during intense foggy/hazy days (+75.8 W/m2) than that during clear sky or less foggy/hazy days (+38 W/m2), mainly due to increase in absorbing aerosols. Whereas SW forcing at surface (SUF) increased from -40 W/m2 during clear sky or less foggy/hazy days to -76 W/m2 during intense foggy/hazy days, mainly due to the scattering aerosols like SO4 2-.

Item Type: Article
Additional Information: Copyright of this article belongs to Springer.
Uncontrolled Keywords: ammonia; black carbon; nitrate; sulfate, aerosol property; air sampling; ammonium; black carbon; chemical composition; clear sky; diurnal variation; emission; fog; haze; light scattering; neutralization; physicochemical property; radiative forcing; semiarid region; spectral analysis; sulfate; trajectory, acidity; aerosol; alkalinity; article; circadian rhythm; cloud; concentration (parameters); fog; India; molecular weight; optical depth; particulate matter; spectral sensitivity; surface property; winter, Agra; Asia; Eurasia; India; South Asia; Uttar Pradesh
Subjects: Meteorology and Climatology
Depositing User: IITM Library
Date Deposited: 13 Feb 2015 10:39
Last Modified: 13 Feb 2015 10:39

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