Meteorological Influences on Seasonal Variations of Air Pollutants (SO2, NO2, O3, CO, PM2.5, and PM10) in the Dhaka Megacity

Abstract

The study was conducted to evaluate the meteorological influences on seasonal variations of air pollutants load in Dhaka city. In this study, we collect air quality data from Darus-salam Continuous Air Monitoring Station (CAMS) and were analyzed to find out their seasonal trends and relation with meteorological parameters. The highest concentration of the major air pollutants showed high values in the dry season (October-April) (SO2=23.45 ppb, NO2=55.33 ppb, O3=11.17 ppb, CO=3.66ppb, PM2.5=125.66 µg/m3, PM10=219 µg/m3) than those of the wet season (May-September) (SO2=10.26 ppb, NO2=16.36 ppb, O3=2.40 ppb, CO=1.23 ppb, PM2.5=39.65 µg/m3, PM10=76.5 µg/m3). These results indicate that higher pollutants load in winter are associated with large scale polluted air transported from the brick kilns situated in the northern surrounds of the observing station which are also related to lower boundary atmospheric heights during winter. However, a reverse relation between rainfall and atmospheric pollution load throughout the wet season was observed. This finding revealed that the lowest concentration levels of pollutants during the wet season are associated with their atmospheric wash out by precipitation. A strong correlation (R2=0.742) was observed between CO and O3 during the study, which indicates the huge production of an oxidant with increasing CO concentration. Interestingly, O3 showed a positive correlation with NO2 (R2=0.391). This result may indicate that NO2 is the important precursors of O3 in this study. Similarly, CO and NO2 showed good correlation (R2=0.68), indicating that both NO2 and CO are produced from similar pathways of photochemical oxidation of VOC. However, PM2.5 and PM10 concentrations showed decreasing trends with the onset of monsoon, indicating washout of atmospheric dust load through rainfall during the wet season.