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Discussion papers
https://doi.org/10.5194/acp-2019-731
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-731
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 26 Nov 2019

Submitted as: research article | 26 Nov 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Atmospheric Chemistry and Physics (ACP).

Space-time variability of ambient PM2.5 diurnal pattern over India from 18-years (2000–2017) of MERRA-2 reanalysis data

Kunal Bali1, Sagnik Dey1,2, Dilip Ganguly1, and Krik R. Smith3,4 Kunal Bali et al.
  • 1Centre for Atmospheric Sciences, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
  • 2Centre of Excellence for Researchon Clean Air, Indian Institute of Technology Delhi, Hauz Khas, New Delhi, India
  • 3School of Public Health, University of California, Berkeley, USA
  • 4Collaborative Clean Air Policy Center, New Delhi, India

Abstract. Estimating ambient PM2.5 (fine particulate matter) concentrations in India over many years is challenging because spatial coverage of ground-based monitoring, while better recently, is still inadequate and satellite-based assessment lacks temporal continuity. Here we analyze MERRA-2 reanalysis aerosol products to estimate PM2.5 at hourly scale to fill the space-time sampling gap. MERRA-2 PM2.5 are calibrated and validated (r = 0.94, slope of the regression = 0.99) against coincident in-situ measurements. We present the first space-time variability of ambient PM2.5 diurnal pattern in India for an 18-year (2000–2017) period. Diurnal amplitude is found to be quite large (> 30 μg m−3) in the Indo-Gangetic Basin (IGB) and western arid regions of India. PM2.5 is found to decrease over the western dust source region and increase over the Himalayan foothills and parts of IGB and central India primarily in the morning and evening hours. This increasing trend at an annual scale is primarily governed by a large increase in concentration during Oct–Feb that can be attributed to a combination of the rise in emission and declining boundary layer height. Our results suggest that the satellite-based concentration estimates (typically representative of late morning to early afternoon hours) are lower (magnitude depends on the place and season) than the 24-hour average concentration in most parts of India. In the future, the integration of reanalysis data in concentration modeling may assist in reducing the uncertainty in estimates of air pollution concentration patterns in India and elsewhere.

Kunal Bali et al.
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Short summary
The ambient PM2.5 concentration has been observed using various in-situ instruments and satellites over India. But none of these observations have been able to cover the complete spatiotemporal coverage. So, here we tried to cover these gaps by using the hourly MERRA-2 aerosol reanalysis data over the Indian region. We hope these results will help formulate better air pollution mitigation plans so that the national burden of disease attributed to ambient air pollution could be decreased.
The ambient PM2.5 concentration has been observed using various in-situ instruments and...
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