Long term observation of surface O3 and its precursors in Dhaka, Bangladesh

Continuous ground-based measurements of O3 and its precursors were conducted in Dhaka, Bangladesh during April 2002–December 2005 in order to investigate ozone precursor characteristics and their distribution. Seasonal and diurnal variations of the O3, CO, NOx and SO2 concentrations — are studied and their possible causes are identified. It is shown that most of the trace gases have peak concentrations in winter and base in monsoon period. Two major emission sources, vehicles and brick kilns, are attributed to the high levels of trace gases in winter. O3 formation was mainly due to local activity and relied on photochemical processes with precursors. The occurrence patterns and the shape of a distribution of trace gases are obtained from histogram distribution. In most cases, the frequency distributions of observed trace gases show a peak to the lower concentration ranges (e.g. 0–10 ppb for O3, 0–500 ppb for CO, 0–20 ppb for NO, NO2 and 0–10 ppb for SO2) with a long tail to the right and unimodal in most of the cases.CO, NOx and SO2 are significantly correlated throughout the entire data set, reflecting the overall influence of anthropogenic emissions.