Wet Deposition of Nitrogen at Different Locations in India

Abstract

The wet deposition data for Pune (2000–2007), for the other locations representing different environments (i.e., urban, rural, industrial, high altitude, marine, traffic etc.) for different time periods during 2001–2007, and for ten Global Atmospheric Watch (GAW) locations in India for a period of 8 years (2000–2007) are considered in this chapter. All the rain water samples were analyzed for pH, conductivity, anions (Cl, SO₄ and NO₃) and cations (NH₄, Na, K, Ca and Mg). In general, in India the rain water was found to be in the alkaline range. Out of ten GAW stations, the 8 years average pH was slightly acidic (pH 5.15–5.36) at only three locations. At the remaining seven locations the pH was alkaline (pH > 5.65). This alkaline nature is due to high dust levels. Neutralization factors indicated that calcium (Ca) is the major neutralizing cation in wet deposition. Calcium concentrations were higher in north and northwestern regions and lower in southern and northeastern regions. Non-sea salt component and back trajectory analyses showed that Ca and SO₄ aerosols were transported to the Indian sub-continent from North African and Gulf countries. The wet deposition fluxes were estimated for all the ionic components including nitrogen (N). The 8 year average annual wet deposition of N for ten locations varied between 4.7 and 34.3 kg N ha⁻¹ year⁻¹ and yearly depositions varied between 1.8 and 57 kg N ha⁻¹ year⁻¹. At all the locations, the NO₃-N depositions were higher compared to NH₄-N. At some of the locations, even though the concentrations are low, the depositions were higher due to the high rainfall amounts. In regional perspective, the excess SO₄-S deposition was higher at an industrial location and the N deposition was higher at a traffic junction in Pune region. At a high altitude rural location (Sinhagad) nearby Pune, the concentrations of excess SO₄, NO₃ and NH₄ were lower but their depositions were higher due to higher rainfall amounts. The total N deposition at four different locations in Pune region varied from 10.4 to 13.2 kg N ha⁻¹ year⁻¹.