Trends in air quality of national capital territory of Delhi.

A set of time series analysis methods viz; regression on deseasonalized data, seasonal regression and regression with weighted least squares technique is suggested to identify the trend in mean monthly ambient air quality data and applied to the case of National Capital Territory of Delhi. The analysis reveals that out of 9 monitored sites NO2 and SO2 increased at 6 sites and SPM level increased at 4 sites. Spatial interpolation using inverse distance square technique was carried out to plot the ambient air quality contours for the years 1990 and 1994 to explain the changes in regional ambient air quality characteristics over the four