Indian Journal of Radio & Space Physics Vol 40, June 2011, pp 147-152 Influence of boundary layer dynamics on pollutant concentrations over urban region – A study using ground based measurements D V Mahalakshmi 1,# , K V S Badarinath 1,$,* & C V Naidu 2 1 Atmospheric Science Section, National Remote Sensing Centre, Dept of Space, Govt of India, Balanagar, Hyderabad 500 625, India 2 Department of Meteorology and Oceanography, Andhra University, Visakhapatnam 530 003 Email: # maha_meteor@yahoo.com, $ badarikvs@yahoo.com Received 23 December 2010; revised 25 April 2011; accepted 3 May 2011 Ventilation coefficient (VC) over urban area of Hyderabad, India during night-time in 2008 has been calculated using night-time mixed layer height with boundary layer lidar (BLL) and radiosonde data to investigate the influence of VC on pollutant concentration. Carbon monoxide (CO), ozone (O 3 ) and black carbon (BC) aerosol mass concentrations in relation to mixed layer height and wind speed have been analysed for different seasons, viz. winter, pre-monsoon, monsoon and post-monsoon associated with boundary layer and ventilation coefficient (VC). The results of the study suggested that VC plays an important role in dispersing the pollutants. Keywords: Ventilation coefficient, Atmospheric boundary layer (ABL) height, Pollutant concentration, Black carbon aerosol, Carbon monoxide aerosol, Ozone aerosol, Aerosol mass concentration PACS Nos: 92.60.Mt; 92.60.Sz 1 Introduction Atmospheric boundary layer (ABL), part of the troposphere, is directly influenced by the land surface processes 1 . The transfer of energy between the surface and the air is partly accomplished by the turbulent eddies. Atmospheric turbulence in the ABL is produced primarily by wind shear and buoyancy. Diurnal variations in wind speed, static instability, turbulent exchange and convective activity in the ABL are significant over tropics 2-3 . Generally, all kinds of energy exchange with surface atmospheric boundary layer plays important role in transporting heat, momentum, moisture besides pollutants such as friction, sensible and latent heat flux occurs in ABL 4-5 . In general, ABL height varies both in time and space, from hundreds of meters to a few kilometers. The ABL height (h) is a crucial parameter in weather and climate models 6 . This height controls the vertical extent, concentration and transformation of atmospheric pollution and has influence on the concentration of trace gases and ozone in the lower troposphere. The vertical mixing of atmospheric pollutants are strongly influenced by the height of the ABL, which acts as an interface between the more polluted regions near the earth’s surface and the relatively cleaner free atmosphere above. Thus, air quality measurements are directly related to the ABL parameters. During daytime, the ground is heated by the sun and a convectively driven, vertically mixed layer grows and reaches its maximum during the afternoon. After sunset, turbulence decays in the mixed layer and a residual layer is formed. The initial mean state and concentration variables of this layer remain that of the daytime mixed layer and change slowly in the absence of advection. During nighttime, temperature decreases throughout the depth of the residual layer and causes neutral stratification. VC plays an important role in dispersion aerosol and is one of the factors that determines the pollution potential. Carbon monoxide (CO), ozone and black carbon (BC) aerosols have a major impact not only on human health and visibility in urban regions, but also on global and regional climate 7-11 . Burning of biomass and fossil fuels, automobile exhaust, forest fires are the major sources of BC. In urban areas, the increasing energy demands for industry and transport propels fossil fuel utilization, which are the major source of pollutants. The BC aerosol and fly ash are unquestionably human produced because its natural sources are negligible. BC is inert in the atmosphere as a result of its chemical structure and also due to its predominant submicron size. Its main atmospheric