Spatial and temporal patterns of air pollutants in rural and urban areas of India Disha Sharma, U.C. Kulshrestha * School of Environmental Sciences, Jawaharlal Nehru University, New Delhi, 110067, India article info Article history: Received 24 February 2014 Received in revised form 30 July 2014 Accepted 26 August 2014 Available online 20 September 2014 Keywords: Air quality parameters SO 2 NO 2 SPM AOD Satellite data abstract In this study, we analysed spatial and temporal patterns of Suspended Particulate Matter (SPM) con- centrations across India. We have also assessed MODIS-derived aerosol optical depth (AOD) variations to characterize the air quality and relate it to SPM, NO 2 and SO 2 in different areas. In addition, the pollutant concentrations have been mapped using geospatial techniques. The results indicated significant differ- ences in air pollutant levels across rural and urban areas. In general, districts of central and northern India had relatively higher SPM concentrations compared to southern India. Out of the top ten SPM polluted districts in India, nine were located in the state of Uttar Pradesh (UP). We observed significant correlations between the SPM and AOD at different sites. Although spatial and temporal patterns of NO 2 and SO 2 matched AOD patterns, the correlation strength (r 2 ) varied based on location. The causes and implications of these findings are presented. © 2014 Elsevier Ltd. All rights reserved. 1. Introduction The presence of particulate matter in the atmosphere can be attributed to both natural as well as anthropogenic processes. The nature of aerosols found in the Indian region may be different from those reported in the other parts of the world (Kulshrestha et al., 2001, 1999; Kafatos et al., 2006). Previously, atmospheric aerosols in Indian region were reported to have significant amounts of soil dust and carbonaceous compounds affecting radiative properties of atmosphere (Kulshrestha et al., 2009; Parashar et al., 2005). High loadings and re-suspension of soil dust lead to high levels of suspended particulate matter (SPM) in the Indian region (Kulshrestha, 2013). The incidents of forest fires also contribute significantly to the emission of carbonaceous aerosols in the country (Vadrevu et al., 2012). Radiative effect of atmospheric aerosols is believed to be of the same magnitude as greenhouse gases (Andreae, 2001). Aerosol components such as black carbon (BC) (Babu et al., 2002), are known to have a warming effect on global climate due to ab- sorption of radiation, whereas others such as, sulphate, organic matter (OM) and mineral matter, cause cooling in the atmosphere as they scatter radiation (Charlson et al., 1992, 1999). Fossil fuel consumption and vehicular emissions along with large industrial point sources add to elevated aerosol fluxes over northern and western India (Reddy and Venkataraman, 2002). The unique variation of energy use across different regions gives rise to temporal and spatial patterns of aerosols distribution over India affecting aerosol optical depth (AOD). AOD is a quantitative measure of the extinction of solar radiation by aerosol scattering and absorption between the point of observation and the top of the atmosphere. It is a measure of the integrated columnar aerosol load and the single most important parameter for eval- uating direct radiative forcing (Kaufman et al., 1997). AOD can be determined from the ground through measurements of the spectral transmission of solar radiation through the atmosphere using rather simple and relatively inexpensive instruments pointed directly at the sun called sun-photometers or filter ra- diometers. Routine ground based AOD observations are of utmost importance for the calibration and validation of AOD retrievals from satellites (Chu et al., 2002; Ichoku et al., 2002). In this study, we present the spatial and temporal variations in SPM over the Indian region. We report typical SPM values and MODIS-derived AOD, in different districts of India and compare levels of SPM in southern and northern India. Relationship between AOD and SPM has also been explored. In addition, we also assessed the relationship between AOD and other pollutants such as SO 2 and NO 2 . * Corresponding author. E-mail address: umeshkulshrestha@gmail.com (U.C. Kulshrestha). Contents lists available at ScienceDirect Environmental Pollution journal homepage: www.elsevier.com/locate/envpol http://dx.doi.org/10.1016/j.envpol.2014.08.026 0269-7491/© 2014 Elsevier Ltd. All rights reserved. Environmental Pollution 195 (2014) 276e281