Preprints
https://doi.org/10.5194/acp-2020-1227
https://doi.org/10.5194/acp-2020-1227

  11 Feb 2021

11 Feb 2021

Review status: this preprint is currently under review for the journal ACP.

Measurement report: An assessment of the impact of a nationwide lockdown on air pollution – a remote sensing perspective over India

Mahesh Pathakoti1, Aarathi Muppalla2, Sayan Hazra3, Mahalakshmi D. Venkata1, Kanchana A. Lakshmi1, Vijay K. Sagar1, Raja Shekhar2, Srinivasulu Jella1, Sesha Sai M. V. Rama1, and Uma Vijayasundaram3 Mahesh Pathakoti et al.
  • 1Analytics and Modelling Division, Land and Atmospheric Physics Division, Earth and Climate Systems Study Division, Atmospheric Chemistry Division, Earth and Climate Sciences Area, National Remote Sensing Centre (NRSC), Indian Space Research Organization (ISRO), Hyderabad-500037, India
  • 2Bhuvan Project Management and Software Evaluation Division, Bhuvan Geoportal and Data Dissemination Area, National Remote Sensing Centre (NRSC), Indian Space Research Organization (ISRO), Hyderabad- 500037, India
  • 3Department of Computer Science, School of Engineering & Technology, Pondicherry University, ChinnaKalapet, Kalapet, Puducherry-605014, India

Abstract. The nationwide lockdown was imposed over India from 25th March to 31st May 2020 with varied relaxations from phase-I to phase-IV to contain the spread of COVID-19. Thus emissions from industrial and transport sectors were halted during lockdown (LD) which resulted in a significant reduction of anthropogenic pollutants. The first two lockdown phases were strictly followed (phase-I and phase-II) and hence are considered as total lockdown (TLD) in this study. Satellite-based tropospheric columnar nitrogen dioxide (TCN) from the years 2015 to 2020, tropospheric columnar carbon monoxide (TCC) during 2019–2020 and aerosol optical depth (AOD550) from the years 2014 to 2020 during phase-I and phase-II LD and pre-LD periods were investigated with observations from Aura/OMI, Sentinel-5P/TROPOMI, and Aqua-Terra/ MODIS satellite sensors. To quantify lockdown induced changes in TCN, TCC, and AOD550, detailed statistical analysis was performed on de-trended data using student’s paired statistical t-test. Results indicate that mean TCN levels over India showed a dip of 18 % compared to the previous year and also against the 5-year mean TCN levels during the phase-I lockdown, which was found statistically significant (p-value <0.05) against the respective period. Furthermore, drastic changes in TCN levels were observed over hotspots namely the eastern region and urban cities. For example, there was a sharp decrease of 62 % and 54 % in TCN levels as compared to 2019 and against 5-years mean TCN levels over New Delhi with a p-value of 0.0002 (which is statistically significant) during total LD. The TCC levels were high in the North East (NE) region during the phase-I LD period, which is mainly attributed to the active fire counts in this region. However, lower TCC levels are observed in the same region due to the diminished fire counts during phase-II. Further, AOD550 is reduced over the country by ~16 % (Aqua and Terra) from the 6-years (2014–2019) mean AOD550 levels, with a significant reduction (Aqua/MODIS 28 %) observed over the Indo-Gangetic plains (IGP) region with a p-value of <<0.05. However, an increase in AOD550 levels (25 % for Terra/MODIS, 15 % for Aqua/ MODIS) was also observed over Central India during LD compared to the preceding year and found significant with a p-value of 0.03. This study also reports the rate of change of TCN levels and AOD550 along with statistical metrics during the LD period.

Mahesh Pathakoti et al.

Status: open (until 08 Apr 2021)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse

Mahesh Pathakoti et al.

Mahesh Pathakoti et al.

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Short summary
Generally, atmospheric pollutants exhibit seasonal and annual variations with space and time besides the episodic events. Hence it is important to quantify the changes that occurred due to episodic events such as lockdown in this case. Therefore in our study, we intended to show the lockdown induced changes of tropospheric NO2, carbon monoxide (CO), and AOD besides the effect of inter-annual variability in these pollutants. Further observed changes were statistically evaluated.
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