Volume 6, No. 4, December 2006, Pages 406-417 PDF(359 KB)
Atmospheric Abundances of Nitrogen Species in Rain and Aerosols Over a Semi-Arid Region: Sources and Deposition Fluxes
Neeraj Rastogi, Manmohan Sarin
Physical Research Laboratory, Ahmedabad-380 009, India
The temporal variation for a three-year period (2000-2002) in the atmospheric abundances of principal nitrogen species (NH4+ and NO3-) has been studied in rain and aerosols from an urban city (Ahmedabad, 23.0°N, 72.6°E) located in a semi-arid region of western India. Their concentrations in ambient aerosols over the annual seasonal cycle exhibit large variation [NH4+: < 0.001 to 1.3 (GM = 0.25 μg/m3); NO3-: 0.09 to 4.4 (GM = 1.3 μg/m3)]; with systematically higher concentrations during Nov-Feb (drier period) and relatively low during Jun-Aug (wet season). In comparison, abundances of NH4+ and NO3- in individual precipitation events (n = 91) collected during the southwest monsoon (Jun-Aug) for three years varied as NH4+: <1.0 to 220 (VWM: 30 μeq/L) and NO3-: 1.3 to 115 (VWM: 13 μeq/L). Using corresponding rainfall data, the wet-deposition fluxes of NH4+ during 2000, 2001 and 2002 have been derived: 364, 327 and 297 mg/m2/y, respectively; which are considerably higher than the dry-deposition fluxes (16, 11 and 16 mg/m2/y). The wet deposition of NO3- over the three years varied as 392, 569 and 487 mg/m2/y in comparison to dry-deposition fluxes averaging as 201, 134 and 137 mg /m2/y. These results also indicate that both dry and wet deposition of NO3- accounts for as much as ~65% of the total inorganic-N species (NH4+ + NO3-), possibly mediated via in-situ chemical reactions of acidic species (NO3- and its precursors) with mineral aerosols. Such regional scale studies are important for quantitative assessment of atmospheric deposition of biogeochemically important trace species and bring to focus the role of semi-arid regions where current knowledge is limited.
Dry and wet deposition; NH4+; NO3-; Aerosol; Precipitation; Semi-arid region; India.