Spatial and temporal analysis of ground level ozone and nitrogen dioxide concentration across the twin cities of Pakistan

The analyses presented in this paper include the concentration levels of NO2 and O-3 measured during 2 successive years in twin cities (Rawalpindi and Islamabad) of Pakistan from November 2009 to March 2011. NO2 was determined using the passive sampling method, while ozone was determined by Model 400E ozone analyzer. The average NO2 and O-3 concentration in twin cities of Pakistan was found to be 44 +/- 6 and 18.2 +/- 1.24 ppb, respectively. Results indicate that the concentration of NO2 and O-3 show seasonal variations. Results also depict that NO2 and O-3 concentration levels are high in areas of intense traffic flow and congestion. Rawalpindi has more elevated levels of NO2 and O-3 as compared to the Islamabad due to the narrow roads, enclosing architecture of road network and congestion. Climatic variables also influenced the NO2 and O-3 concentration, i.e., temperature is positively related with O-3, while negatively related with NO2, relative humidity is directly related with NO2 and inversely related with O-3, whereas rainfall show negative association with both NO2 and O-3 concentration. Comparing the results with WHO standards reveals that NO2 concentration levels at all the sampling points are above the permissible limit, while ozone concentration is still lower than the WHO standards. Thus, there is a need to take appropriate steps to control these continuously increasing levels of NO2 and O-3 before they become a serious hazard for the environment and people living in those areas.