Assessment of atmospheric assimilation potential for industrial development in an urban environment: Kochi (India)

The assimilation potential (assimilative capacity) of the atmosphere can be represented in two ways: one as the ventilation coefficient and the other as the dispersion potential of emission loads discharged into the region. In the present study, the atmospheric assimilation potential of a typical urban area in Kochi city has been determined with respect to sulfur dioxide (SO2). The ventilation coefficient is directly proportional to the assimilation potential of the atmosphere and has been computed using meteorological parameters in all four seasons (winter, summer, monsoon and post-monsoon) of the years 1998–1999 represented by January, April, July and October respectively. The diurnal variation in ventilation coefficients shows that the assimilative capacity of the atmosphere is high during the afternoon and is reduced during the evening and morning in all the seasons. Among all the seasons, monsoon and post-monsoon have the poorest assimilative capacity throughout the day. In the second approach, the assimilation potential is estimated through dispersion modelling in terms of the concentration of pollutants, which is inversely proportional to the assimilative capacity of the atmosphere. The Industrial Source Complex (ISC) dispersion model for point sources has been used to predict the spatial and temporal distribution of SO2 under three different industrial scenarios (type of industries existing in the Kochi region, refinery and power plant). The model predictions indicate that monsoon is the most critical season having maximum pollution, followed by summer and post-monsoon. Lowest pollution was observed in winter. The assimilative capacity in terms of the ventilation coefficient is very poor indicating high pollution potential in all the seasons. However, dispersion modeling suggests that if industrial development is planned properly, additional industrial sources can be accommodated by restricting the emission loads to be within the assimilation potential of the region.