CNG; Diesel; Public transport; Air pollution; Vehicles
The present study discusses the ambient air quality of Delhi from the point of view of change of diesel by Compressed Natural Gas (CNG) in transportation in Delhi. Several initiatives were taken to reduce extremely high levels of pollutants present in the ambient air of urban city. One of the initiatives was to move public transport to CNG, which has been implemented in Delhi since April 2001. Delhi boasted CNG in nearly 2200 buses, 25,000 three wheelers, 6000 taxis and 10,000 cars. However, more than half of the vehicles are yet to be changed to CNG.
A relative comparison of ambient air concentration of pollutants, e.g. carbon monoxide (CO), sulphur dioxide (SO2), suspended particulate matter (SPM) and oxides of nitrogen (NOX), emitted from transport sector, during the years 1995–2000 (without CNG) and the year 2001 (with CNG) has been made in order to assess the impact of CNG vehicles on ambient air quality in Delhi. It has been found that concentration contribution of above pollutants has been reduced considerably.
The annual average concentration of SPM came down to 347 from 405 μg m−3, which is still beyond the permissible limits. The concentration of annual averages of CO, SO2 and NOX decreased to 4197 from 4681 μg m−3, 14 from 18 μg m−3 and 34 from 36 μg m−3, respectively, and are well within the permissible limits. An analysis of SO2/NOX and CO/NOX concentrations, whose correlation coefficient r2 has the values 0.7613 and 0.7903, respectively, indicates that point sources are contributing to SO2 and mobile sources are contributing to NOX concentrations.