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

► Ambient levels of O3, CO, NOx and SO2 are investigated from long term (2002-2005) measurements in Dhaka. ► Characteristics of trace gases and their influential factors are elucidated. ► Two major emission sources, vehicles and brick kilns, are attributed to the high levels of trace gases in winter. ► O3 in all seasons show peaks between 14:00-15:00 while other gases show peaks during the rush traffic hours.