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Global fine-scale changes in ambient NO2 during COVID-19 lockdowns.

Matthew J Cooper1,2, Randall V Martin3,4,5, Melanie S Hammer3,4

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COVID-19 lockdowns significantly reduced nitrogen dioxide (NO2) air pollution globally. Satellite data revealed NO2 concentrations dropped by 29% in strict lockdown countries, offering crucial insights into air quality changes.

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Area of Science:

  • Atmospheric chemistry and air pollution monitoring
  • Environmental science and public health

Background:

  • Nitrogen dioxide (NO2) is a major air pollutant with significant health impacts.
  • COVID-19 lockdowns led to reported decreases in NO2 concentrations globally.
  • Uncertainty exists regarding satellite NO2 data's relation to ground-level concentrations and global representativeness.

Purpose of the Study:

  • To derive spatially resolved, global ground-level NO2 concentrations from satellite data.
  • To assess NO2 changes in over 200 cities during COVID-19 lockdowns (2020 vs. 2019).
  • To evaluate the impact of lockdowns on NO2 concentrations, especially in areas lacking ground monitoring.

Main Methods:

  • Utilized TROPOMI satellite data to derive NO2 column densities at ~1 km resolution.
  • Calculated global ground-level NO2 concentrations from satellite observations.
  • Compared NO2 concentrations in 2020 (lockdown) with 2019 across numerous cities worldwide.

Main Results:

  • Found mean country-level population-weighted NO2 concentrations were 29% ± 3% lower in countries with strict lockdowns.
  • Quantified NO2 reductions in over 200 cities, including 65 cities without ground monitoring.
  • Observed NO2 decreases during lockdowns exceeded recent emission control reductions, equivalent to 15 ± 4 years of global reduction.

Conclusions:

  • Spatially resolved satellite-derived NO2 estimates are crucial for assessing air quality changes, especially in data-scarce regions.
  • Lockdown impacts on NO2 vary by country and emission sector, highlighting the need for localized data.
  • Satellite-based NO2 monitoring provides valuable insights into the effectiveness of emission reduction strategies.