Satellite-Derived PM2.5 Data Across India

Dr. Sagnik Dey and Dr. Dilip Ganguly at IIT-Delhi have been working on the a new project entitled- Satellite-Based Application For Air Quality Monitoring and Management at National Scale (SAANS). The project is supported by the Central Pollution Control Board (CPCB) and the Ministry of Environment, Forests and Climate Change (MoEFCC).

Can you tell us about the SAANS project?

The SAANS project is conceptualized to fill in the spatial data gap in PM2.5 monitoring in India under the National Clean Air Program (funded by the Central Pollution Control Board). We developed the algorithm based on global studies and our own research with several modifications. First, we processed the MAIAC AOD data at 1 km resolution. We converted AOD (aerosol optical depth) to PM2.5 using a temporally and spatially varying scaling factor. Earlier we used the GEOS-Chem derived scaling factors from Randall Martin’s group. Since running chemical transport models (CTM) is resource-intensive and we cannot assume the scaling factor to be static over time (i.e. same value for every 1st Jan, eg.), we processed MERRA-2 reanalysis data to derive the scaling factor. We calibrated the factor using the ground-based measurements, interpolated to match the satellite AOD resolution. Once the AOD is converted to PM2.5, we further use a diurnal scaling factor from the reanalysis data to convert the instantaneous PM2.5 (during the satellite overpass between 10 am to 2 pm Indian time) to 24-hr average PM2.5. From the daily product, one can then estimate monthly or annual statistics. We generated data from Feb 2000 till now. We are satisfied with the quality of the data (based on the rigorous evaluation process with CPCB data). 

What data are available and in what format? How can people access them?

We are building a web portal SAANS to disseminate the monthly and annual PM2.5 product in NetCDF format for use in air quality and epidemiological studies. Currently, the MoEFCC and CPCB are examining the data and yet to give their formal approval. More about the methodology here.

How was this project funded? Do you plan to make updates in the future?

The project was funded by the CPCB under the NCAP. We plan to help CPCB with this data in (a) identifying the local hotspots, (2) tracking temporal trends in urban and rural air quality, (c) tracking the pollution build-up, (d) delineating the major airsheds of India, (e) identifying the suitable locations for future deployment of ground-based sensors. We are in the process of exploring the AOD products from geostationary satellites – INSAT-3D and GEMS (when available) for PM2.5 retrieval.
In future, we want to be engaged in (a) develop PM2.5 speciated product for the country to advance air pollution epidemiological research, (b) explore the use of machine learning in air quality management, and (c) develop a hybrid monitoring system for India. We are already involved in deploying a low-cost sensor network cross the Gangetic Plain in collaboration with RTI, NASA, University of California Berkeley and CEEW.

What are the possibilities for using this data for research & advocacy?

We feel that having a national database has a lot of opportunities for research, capacity building, awareness and advocacy. I must appreciate the CPCB for being one of the first regulatory agencies in the world to explore the use of alternate monitoring for air quality management. Their interest and involvement in using satellite data in tandem with the ground-based network for air quality management is an encouraging and positive sign for the country like India, where the air pollution has been identified as the largest environmental health risk.

For more information, please contact Dr. Sagnik Dey.

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