CNG (compressed natural gas) was fully implemented in public transport system in Delhi in December 2002. The study assesses the benzene concentration trends at two busy traffic intersections and a background site in Delhi, India. Monitoring was done for two different time periods viz; in the year 2001-2002 (pre-CNG) and two winter months (January and February) of the year 2007 (post-CNG) to assess the impact of various policy measures adopted by the government of Delhi to improve the air quality in the city. Annual average benzene concentration for the pre-CNG period was found to be 86.47 +/- 53.24 mu g m(-3). Average benzene concentrations for the winter months (January-February) of pre- and post-CNG periods were 116.32 +/- 51.65 mu g m(-3) and 187.49 +/- 22.50 mu g m(-3), respectively. Enhanced values could be solely attributed to the increase in the vehicular population from 3.5 million in the year 2001-2002 to similar to 5.1 millions in the year 2007. (c) 2007 Elsevier B.V. All rights reserved.