The Cumulative Impacts of Emissions from Thermal Power Plants on the Air Quality of Karachi through AERMOD Modeling.

Abstract

The quality of air emissions in Pakistani mega cities is one of the worst in the world. Urban air contamination is assessed to be responsible of 0.865 M unexpected losses consistently and about 60% of these passing’s happen in Asia, continuous increase in urbanization, industrialization and motorization caused a substantial rise in various air pollutants, which has notable impacts on human health and environment. Environmental Impact Assessment is mandatory for future projects in Pakistan, but Cumulative Impact Assessment (CIA) process is not available in the country, the mega city like Karachi needs strict criteria to overcome the air quality issue on priority basis therefore, AERMOD Model along with ArcGIS have been used to provide a practical CIA tool to Sindh Environmental Protection Agency. In this study five proposed thermal power plants of total 3440-50 MW were selected where two types of cumulative impacts were modeled. The short-term cumulative impacts of Nitrous Oxides (NOx) and Sulphur Dioxide (SO2) were considered as 1-h and 24- h, whereas long term were considered as annual. The results of NOx emissions were 170 μg/m3 for 1st percentile 1-h, 33 μg/m3 for 1st percentile 24-h and 1st percentile annual was 14.5 μg/m3. While the SO2 emissions were 199 μg/m3 for 1st percentile 1-h, 29.8 μg/m3 for 1st percentile 24-h and long-term 1st percentile annual was 7.5 μg/m3 respectively. All the limits are complying with national and international standards because, the wind speed (5-8 m/s) and wind direction has a substantial impact on flow field which results in lowering the ground level concentrations of the pollutants in the study area. This is further caused by the strong sea breeze from the Arabian Sea which is termed as blessing for the residents of the study area.