Particulate Matter Air quality in New Delhi Metropolitan in India
The capital of India, Delhi, is one of the 10 most polluted cities in the world with a human population of 14 million (Goyal et al., 2003). The estimated emission of pollutants from automobiles in Delhi exceeds 1300 tons every year (Goyal et al., 2003) and contributes almost 70% of the total pollution in Delhi. However, depending on local meteorological conditions, high concentrations of PM could also come from natural dust, which could be transported to the site or local road side dust. The overall contribution of dust in PM2.5 is less compared to its contribution to PM10 mass but during dust storm and summer time when wind speed is sufficient high, dust could contribute as much as 20 % to the total PM2.5 mass (Hueglin et al., 2005; Zheng et al., 2005). Delhi also has three major thermal power plants in its vicinity which contribute approximately 13% to the total pollution in Delhi (Goyal et al., 2003). Figure 2d presents the data from Delhi during the year 2003. The PM2.5 data over Delhi are limited and only available from July 23 to November 03, 2003. However MODIS AOT data are analyzed for the entire year. Although the air quality of Delhi has improved in recent years, PM2.5 concentration in the city ranges from 36 to 52 ?gm-3, which is two-three times higher than that in Sydney. Here it is important to note that the population of Sydney is around 4.5 million, which is almost one-third of the population in Delhi. The monthly mean AOT values are high during summer and low in winter. The peak AOT was observed in May with an AOT value of 0.9 and the minimum was reported as 0.38 in the February. The AOT value begins to decline as the Monsoon approaches Delhi in the late July or early August, and the decline in the trend of AOT continues until December as a result of washout by the monsoon rain. The winter months (December to February) in Delhi are dominated by cold, dry air and wind speed as low as 1 ms-1 with ground level inversion, which is one of the reasons for low values of AOT during winter (Goyal et al., 2002).
Figure 1. Time Series of aerosol optical depth and PM2.5 mass concentration over New Delhi, India.
Figure 2. Scatter plot between MODIS aerosol optical depth and PM2.5 mass concentration over New Delhi, India.
Figure 3. Monthly mean satellite derived particulate matter air quality over New Delhi, India using first approximated relationship between PM2.5 and MODIS AODs.
Reference
Gupta, P., S.A. Christopher, J. Wang, R. Gehrig, Y.C. Lee, N. Kumar, (2006), Satellite Remote Sensing of Particulate Matter and Air Quality over Global Cities, Atmospheric Environment, 40, 5880-5892. (abstract) (full text)
Kumar, N., A. Chu, and A. Foster, An empirical relationship between PM2.5 and aerosol optical depth in Delhi metropolitan, Atmospheric Environment, 41, 4492-4503, 2007.
Kumar, N., A. Chu, and A. Foster, Remote sensing of ambient particles in Delhi and its environs : estimation and validation, International Journal of Remote Sensing, 29 :12, 3383-3405, 2008.