Atmospheric Wet and Dry Depositions of Ions over an Urban Location in South-West India

Wet deposition (WD) and Dry deposition (DD) samples were collected during a period of 4 year (2006 to 2009), at four different sites representing different surroundings around Pune city in southwest India. The samples were collected on a daily basis for WD and weekly basis for DD. These samples were analyzed for major ionic components e. g., Cl-, NO3-, SO42-, Na+, K+, NH4+, Ca2+ and Mg2+. Both the WD and DD were alkaline (pH > 5.6) at all the four sites. The WD fluxes of all the ionic components were higher than the DD fluxes, except at the traffic junction Swargate, where majority of the species appeared with much higher DD fluxes than WD fluxes (68% for NO3-, 63% for Ca2+, 60% for Mg2+, 57% for K+). WD flux of NH4+ is higher (64-80%) than the DD flux at three locations and slightly lower (48%) at a high altitude location. In case of sea salt (Na and Cl), WD fluxes were higher (63-90%) than the DD fluxes at all the four locations. The dominant ion in DD was NO3- at Pashan (semi-urban) and Sinhagad (high altitude), Ca2+ at Swargate (traffic junction) and SO42- at Bhosari (industrial). The difference in deposition fluxes between the four sites was attributed to the effect of the local sources. Deposition velocities of SO42- and NH4+ were < 1 cm/s while Ca2+, Mg2+, Na+, K+, NO3-, and Cl- exhibited deposition velocities >= 1 cm/s. At one of the sites Pashan, where the earlier data is available; DD rates showed increase in all the chemical components, except for NH4+ after a period of about 2 decades.