Ground-level concentration of nitrogen oxides (NOx) at some traffic intersection points in Calcutta

Results from a year long programme of measuring ground-level concentration of NOx at 19 important traffic intersection points within the city of Calcutta have been presented. Fortnightly measurements were made with a set of three passive samplers along with a control deployed at each of the sites. Results indicate that the NOx concentration level has a seasonal variation. Maximum average concentration of 222 μg m−3 was observed during winter and a minimum average concentration of 55 μg m−3 was observed during peak monsoon.