Sub-micron particle size distribution and temperature were measured at six levels immediately above the ground surface during 8-16 December 1997 and 24-28 December 1998. Diurnal observations were made at every three-hour interval at all the levels. Continuous measurements of aerosol concentration were made from 0300 to 1000 h at 1 m level. During this period, particle concentration decreases from 0300 h, attains a minimum value between 0600 and 0700 h, and then maximum at 0900 h. Particles greater than or equal to 0.075 mum show systematic variation in concentration, whereas particles < 0.075 mum show large fluctuations with time during 0300 to 1000 h. Concentration of particles of sizes 0.075-0.75 mum shows a minimum at 15-cm level where the temperature is maximum. However, particles of size 0.013 mum undergo Brownian diffusion and thus do not show any trend with temperature. The phenomena of thermophoresis and fog scavenging are discussed in terms of these results.
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