Measurements and analysis of air quality in Islamabad, Pakistan

Abstract

AbstractAmbient air quality of Islamabad, Pakistan, reveals that annual average mass concentration of particulate matter (PM2.5) (∼45 to ∼95 µg m−3) and nitric oxide (NO) (∼41 to ∼120 µg m−3) exceeds the Pakistan's National Environmental Quality Standards (NEQS). The annual ozone (O3) concentration is within the permissible limits; however, some of the hourly concentration exceeds the NEQS mostly during the summer months. Correlation studies suggest that carbon monoxide (CO) has a significant (p‐value ≤ 0.01) positive correlation with NO and NOy′; whereas, with O3, a significant (p‐value ≤ 0.01) negative correlation is observed. The regression analysis estimates the background CO concentration to be ∼300 to ∼600 ppbv in Islamabad. The higher ratio of CO/NO (∼10) suggests that mobile sources are the major contributor to NO concentration. On the other hand, the ratio analysis of sulfur dioxide (SO2)/NO for Islamabad (∼0.011) indicates that the point sources are contributing to SO2 in the city. NO and SO2 correlation indicates contribution of direct sulfur emission sources. Ratios of [CO] to [NO] and [SO2] to [NO], based on ambient air quality measurements, provide a test for emission inventories. The ratios of these pollutants in the available Islamabad emission inventories are consistent with ambient values for these pollutants. The correlation of PM2.5 and NO suggests that a fraction of secondary PM2.5 is produced by chemical conversion of NO into nitrates. The regional background O3 concentration for Islamabad has been determined to be ∼31 ppbv. This study suggests that there is an increase in O3 concentration with increases in photochemical conversion of NO to reservoir NOy′ species.