Abstract:
Air pollution is one of the emerging issues in most of the cities of Pakistan. According to US AQI, Lahore stands second among the most polluted cities of the world. So, there is an utmost need of air quality monitoring in the country. Increasing traffic load, industrial development and constructional activities are contributing to air pollution. Air quality standards are regulated by monitoring criteria pollutants such as NO2. NO2 is a major contributor to form photochemical smog, acid rain, tropospheric ozone and several other secondary pollutants. This study was designed to monitor NO2 in three major cities (Lahore, Islamabad and Multan) of Pakistan. Lahore was selected as the key study area; fixed monitoring was carried out at two different locations at Lahore and one site in Islamabad by using MAX-DOAS. Several field campaigns were also carried out within and around the (Lahore, Islamabad and Multan) cities by using Car MAX-DOAS. NO2 diurnal, weekly and annual cycle were observed. Results shows NO2 concentration was higher in morning and evening but lower in the noon due to photolysis of NO2. It was also observed that NO2 was lowest on Friday (Business holiday), while annual cycle shows highest average concentrations in winters and lowest in summers over Islamabad. NO2 concentrations were occasionally exceeding Pak-NEQS limit (42.5 ppb) in Lahore, whereas Multan and Islamabad were within permissible limit during field campaign. NO2 MAX-DOAS measurements were also compared with OMI satellite observations and found a similar spatial distribution of NO2. A good correlation was observed when MAX-DOAS data was averaged for 01-02 pm (PST) and compared with OMI observations, as the satellite passes over Pakistan between 01-02 pm (PST). However, OMI satellite underestimate the NO2 concentration as compare to ground based MAX-DOAS observations.
