Natural processes dominate the pollution levels during COVID-19 lockdown over India

Venkat Ratnam Madineni,Prasad Perumal,Ibrahim Hoteit,Hari Prasad Dasari,Yesubabu Viswanadhapalli,Ramakrishna Karumuri

doi:10.1038/s41598-021-94373-4

Abstract

The lockdown measures that were taken to combat the COVID-19 pandemic minimized anthropogenic activities and created natural laboratory conditions for studying air quality. Both observations and WRF-Chem simulations show a 20–50% reduction (compared to pre-lockdown and same period of previous year) in the concentrations of most aerosols and trace gases over Northwest India, the Indo Gangetic Plain (IGP), and the Northeast Indian regions. It is shown that this was mainly due to a 70–80% increase in the height of the boundary layer and the low emissions during lockdown. However, a 60–70% increase in the pollutants levels was observed over Central and South India including the Arabian sea and Bay of Bengal during this period, which is attributed to natural processes. Elevated (dust) aerosol layers are transported from the Middle East and Africa via long-range transport, and a decrease in the wind speed (20–40%) caused these aerosols to stagnate, enhancing the aerosol levels over Central and Southern India. A 40–60% increase in relative humidity further amplified aerosol concentrations. The results of this study suggest that besides emissions, natural processes including background meteorology and dynamics, play a crucial role in the pollution concentrations over the Indian sub-continent.

Highlights

The lockdown measures that were taken to combat the COVID-19 pandemic minimized anthropogenic activities and created natural laboratory conditions for studying air quality
Observations based analyses have shown that lockdown measures implemented to combat COVID-19 has led to significant improvement in air quality over India, during the first phase of the lockdown (i.e., March 25 to April 14, 2020)
We demonstrated that an elevated aerosol layer, through long-range transport, a decrease in background wind speed, an increase in relative humidity, and no significant change in the boundary layer altitude are the main reasons behind the observed increase in the aerosol optical depth during lock down over Central I ndia[44]

Summary

Introduction

The lockdown measures that were taken to combat the COVID-19 pandemic minimized anthropogenic activities and created natural laboratory conditions for studying air quality Both observations and WRF-Chem simulations show a 20–50% reduction (compared to pre-lockdown and same period of previous year) in the concentrations of most aerosols and trace gases over Northwest India, the Indo Gangetic Plain (IGP), and the Northeast Indian regions. The restrictive measures taken by the government of India to minimize the spread of COVID-19 improved the air quality standards as a result of the significant reduction in anthropogenic activities. An AQI assessment over New D elhi[33] indicated a significant reduction in pollution, such as a 50% reduction in coarse and fine particulate matter ( PM10 and PM2.5), a 52% reduction in N O2, and a 30% increase in CO concentrations All these studies suggested a clear increase in O 3 during the lockdown, which was attributed to changes in the amount of N Ox and volatile organic compounds in the atmosphere. An increase in O3 was reported in Rome, Turin, and Wuhan during lockdown, by 14%, 27%, and 36%, r espectively[35]

Methods

Results

Discussion

Conclusion