Dry deposition modeling of atmospheric particles and seasonal spatial variations of sulphur dioxide concentration in a typical medium level indian city Karaikudi

Abstract

In this study, Karaikudi, a medium level Indian city has been chosen to assess dry deposition. The sampling locations have been categorized into three Zones viz: Zone 1, Zone 2 and Zone 3. Zone 1 was classified where traffic is expected to be high. Combinations of traffic and residential area have been designated as Zone 2 whereas Zone 3 meant purely for residential area alone. Under Zone 1, sampling locations were chosen as New bus stand and Old bus stand. Tower Junction and Sri Ram nagar governed by Zone2 whereas Zone 3 comprised Police colony and Burma colony Daytime and nighttime dry deposition flux and particle concentration of particulate matter were measured. Samples were collected by dry deposition sampler (Eagle II arrangement) containing a knife edged surrogate surface. Day time and nighttime samples were collected from 8 am to 8 pm and 8 pm to 8 am respectively. Particle concentration was measured by using High Volume Sampler (HVS). Wind speed was obtained with digital anemometer (make: Lutron AM-4201). Particle size was measured by using X ray Diffractometer (XRD). 92 samples of dry deposition flux and particle concentration were collected in Karaikudi during period of no rain or threat of rain. Among all sampling locations the highest dry deposition flux was measured as 934.05 mg/m2/h in the month of May 07 at New bus stand (Zone 1) sampling location whereas minimum dry deposition flux was obtained as 7.106 mg/m2/h at Police colony sampling location (Zone 3). Highest and lowest particulate concentrations were obtained as 356.21 g/m3 and 3.27 g/m3. Dry deposition velocity was calculated from measured dry deposition flux and particle concentration. Maximum dry deposition velocity obtained was 135.07 cm/s and the minimum was 26.49 cm/s. In most sampling locations, the fluxes of total mass and particle concentration during daytime were higher than nighttime due to higher wind speed. For most of the observations, linear correlation was obtained between dry deposition flux and wind speed.