Chimurkar D. Navinya, V. Vinoj , Satyendra K. Pandey

School of Earth, Ocean and Climate Science Indian Institute of Technology Bhubaneswar, Jatni – 752050, Odisha, India

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Navinya, C.D., Vinoj, V. and Pandey, S.K. (2020). Evaluation of PM2.5 Surface Concentrations Simulated by NASA’s MERRA Version 2 Aerosol Reanalysis over India and its Relation to the Air Quality Index. Aerosol Air Qual. Res.,


  • MERRA2 PM2.5 is evaluated against ground-based measurements over the Indian region.
  • The concentration of PM2.5 is relatively low biased compared to observation.
  • A simple bias-correction improves the concentration for air-quality purposes.
  • The percentage exceedance of bad air quality days was reasonably good after correction.


The PM2.5 or particulate matter mass up to 2.5 micron in size is one of the essential components of air pollution closely linked to an adverse effect on human health. Its continued exposure results in a significant number of premature mortality. The limited number of surface measurements and lack of observations with sufficient spatial resolution hampers studies related to air pollution and its impact on various societally relevant issues. In recent times, aerosol reanalysis, such as National Aeronautics and Space Administration’s Modern-Era Retrospective Analysis for Research and Applications, version 2 (MERRA-2), have started providing global distribution of PM2.5 mass concentration estimates at high spatio-temporal resolutions. However, limitations in their estimation methodologies necessitate careful evaluation so that their strengths and limitations are well understood. In this paper, the assessment of PM2.5 estimates from MERRA2 is performed against ground-based PM2.5 measurements at 20 stations across the Indian region during the period 2015 to early 2018. Our analysis shows that MERRA2 generally underestimates PM2.5 both in terms of mass concentrations and exceedance days. While the Central Pollution Control Board (CPCB) PM2.5 measurements report exceedances from the national ambient air quality standards (NAAQS) for 34% of the time, it is only 11% for MERRA2. Annually averaged over all sites, MERRA2 PM2.5 is low biased by about 27 µg m-3. The correlation between measurements and MERRA2 was (0.6) 0.96 for temporal averaging at (daily) monthly time scales. A simple bias correction improves these correlations dramatically on daily and monthly time scales. Overall, our evaluation reveals that the raw estimates of MERRA2 PM2.5 on time scales of monthly and above are beneficial for long term air quality studies.

Keywords: PM2.5, CPCB, MERRA-2, Air Pollution, Aerosols, Evaluation

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