Lekinwala, NL; Bhardwaj, A; Raman, RS; Bhushan, M; Bali, K; Dey, S (2020). A framework for setting up a country-wide network of regional surface PM2.5 sampling sites utilising a satellite-derived proxy - The COALESCE project, India. ATMOSPHERIC ENVIRONMENT, 234, 117544.

Air quality management and assessment of aerosol climate effects over a large area require the strategic placement of regionally representative monitoring sites (RRMS) to capture the required information. Ground-based, fine particulate matter (PM2.5) concentrations measured for a long duration at high spatial resolution i. e. at several potential locations in a region help identify an optimal regionally representative site for the monitoring network. However, in the absence of long-term PM2.5 concentrations with high spatial resolution, identification of RRMS is a challenge. To identify for such situations, a novel methodology utilising satellite-derived PM2.5 is presented in this study. High spatial resolution (1 km x 1 km) daily aerosol optical depth (AOD) over several years (2004-2011) is used to derive surface PM2.5 using appropriate conversion factors. PM2.5 concentrations thus derived for a potential site and its nearby cells in the region are subjected to statistical analysis, to quantify linear/non-linear relationships between the respective PM2.5 time-series. Metrics such as coefficient of divergence (CoD), Pearson correlation coefficient (PCC) and Mutual information (MI) are calculated to assess the regional representativeness of a site. These criteria combined with physical criteria such as proximity of the site to local sources, local meteorology analysis and clustered air parcel back-trajectory analysis, are used in a weight-of-evidence approach to establish site adequacy. The selection and validation of eleven sites for the COALESCE project, is used as an illustrative example, to demonstrate the effectiveness of the site-selection methodology developed in this study.