6. Air Pollution Scenario over Delhi City

The rise in population and growth in economic activity have led to an increase in pollution in Delhi. About 55 % of Delhi’s population live within 500 m of the roads with a high level of pollution which leads to higher exposure of population to air pollutants, thus resulting in health problems. In order to analyse the air pollution scenario in Delhi, a study has been conducted of the different criteria pollutants, e.g. NO₂, SO₂, CO, PM_2.5 and PM₁₀, along with a study of surface ozone (O₃) for the period 2008–2011. The data of 10 stations of the air quality monitoring network of the India Meteorological Department along with the data collected by the Central Pollution Control Board have been analysed. The data of respirable suspended particulate matter (RSPM) shows that its concentration in Delhi’s air is double that of the national limit. Significant changes have been noticed from year to year in concentrations of all pollutants in Delhi, which may be due to meteorological factors and changes in emissions from different sources of air pollutants. The level of surface ozone has been found rising due to high vehicular emissions in the city. The inverse relationship between surface ozone concentration and relative humidity indicates that the major photochemical paths for the removal of ozone become effective when humidity increases in Delhi. The study of CO/NOx ratios in comparison to ratios of SO₂/NOx reveals that CO/NOx ratios are higher which indicates that vehicular emissions are the major sources of air pollution in Delhi.