Unchanged PM<sub>2.5</sub> levels over Europe during COVID-19 were buffered by ammonia

Evangeliou, Nikolaos; Tichý, Ondřej; Svendby Otervik, Marit; Eckhardt, Sabine; Balkanski, Yves; Hauglustaine, Didier A.

doi:https://doi.org/10.5194/ar-3-155-2025

Articles | Volume 3, issue 1

https://doi.org/10.5194/ar-3-155-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

https://doi.org/10.5194/ar-3-155-2025

© Author(s) 2025. This work is distributed under
the Creative Commons Attribution 4.0 License.

Articles | Volume 3, issue 1

Research article

|

28 Mar 2025

Research article |

| 28 Mar 2025

Unchanged PM_2.5 levels over Europe during COVID-19 were buffered by ammonia

Nikolaos Evangeliou, Ondřej Tichý, Marit Svendby Otervik, Sabine Eckhardt, Yves Balkanski, and Didier A. Hauglustaine

Supplement

https://doi.org/10.5194/ar-3-155-2025-supplement

Data sets

Unchanged PM2.5 levels over Europe during COVID-19 were buffered by ammonia Nikolaos Evangeliou et al. https://doi.org/10.5061/dryad.12jm63z1q

Accounting for Non-Detects: Application to Satellite Ammonia Observations (https://hpfx.collab.science.gc.ca/~mas001/satellite_ext/ cris/snpp/nh3/v1_6_4/) Evan White et al. https://doi.org/10.3390/rs15102610

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Short summary

The COVID-19 lockdown measures in 2020 reduced emissions of various substances, improving air quality. However, PM_2.5 stayed unchanged due to NH₃ and related chemical transformations. Higher humidity favoured more SO₄^2- production, as did the accumulated NH₃. Excess NH₃ reacted with HNO₃ to make NO₃^-. In high-NH₃ conditions such as those in 2020, a small reduction in NO_x levels drove faster oxidation of NO₃^- and slower deposition of total inorganic NO₃^-, causing high secondary PM_2.5.