Lessons from the COVID-19 air pollution decrease in Spain: Now what?

Area of Science:

• Environmental Science
• Atmospheric Chemistry
• Public Health

Background:

• The COVID-19 pandemic triggered unprecedented reductions in human activity, including traffic, leading to significant air quality changes.
• Understanding these changes is crucial for developing effective long-term pollution abatement strategies.
• Spain's metropolises experienced varied air quality responses during lockdown and relaxation periods.

Purpose of the Study:

• To analyze COVID-19-driven air quality shifts across 11 Spanish metropolises.
• To identify lessons learned for ongoing pollution control.
• To assess the impact of reduced mobility and behavioral changes on air pollutants.

Main Methods:

• Analysis of air quality data (NO₂, PM_2.5, PM₁₀, O₃) during COVID-19 lockdown and relaxation periods.
• Comparison with World Health Organization Air Quality Guidelines (WHOAQGs).
• Consideration of traffic flow changes, modal shifts (public vs. private transport), agricultural emissions, and meteorological conditions.

Main Results:

• Traffic flow decreased by up to 80%; NO₂ levels dropped below 50% of WHOAQGs.
• PM_2.5 reductions were less significant than expected due to increased agricultural/biomass burning and secondary aerosol formation.
• PM₁₀ decreased more than PM_2.5 due to reduced road dust and construction.
• Ozone (O₃) responses were heterogeneous in urban areas, with some cities exceeding WHOAQGs.
• A shift to private vehicles post-lockdown was observed, driven by infection fears.

Conclusions:

• While lockdowns improved NO₂ levels, PM_2.5 and O₃ abatement requires addressing non-traffic emission sources.
• The shift to private vehicles poses a challenge for sustained air quality improvements.
• Further modeling is needed to pinpoint precursor reduction targets for secondary pollutants like O₃ and PM_2.5.