Have cNG regulations in Delhi Done t heir Job

Air quality interventions are a new phenomenon in the rapidly growing megacities of developing countries. The enforcement of compressed natural gas (CNG) in Delhi (India) and Lahore (Pakistan) are two examples of such interventions, which have drawn the attention of media, the public and researchers worldwide. As a result, there is an increasing interest in the understanding of the impact of these interventions on the time-space dynamics of air pollution and their effect, in turn, on human health. The limited spatial-temporal coverage of air pollution data, however, restricts our ability to evaluate the impact of such interventions. The sequential details on CNG regulations in Delhi and associated environmental laws are available in Bell et al (2004). A few studies have attempted to evaluate the levels of air pollution in Delhi in pre- and post-intervention periods. For example, Kathuria (2005) examined the short- and long-term effects of CNG regulations in Delhi. He used air pollution data from 1999 to 2003, monitored at a central site near the income tax office (ITO) in Delhi, and employed an autoregressive model to indirectly evaluate the levels of air pollution before and after the regulations. Although the results of his analysis do not suggest any significant improvement in air quality, as measured by PM 10 , total suspended particulate (TSP) matter and nitrogen oxides (NO x ), after the CNG regulations, it does not imply that the emission levels did not drop from the targeted sources – buses, autorickshaws and taxis.