Modelling the impacts of emission changes on O<sub>3</sub> sensitivity, atmospheric oxidation capacity, and pollution transport over the Catalonia region
<p>Tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>) is an important surface pollutant in urban areas, and it has complex formation mechanisms that depend on the atmospheric chemistry and on meteorological factors. The severe reductions ob...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-09-01
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| Series: | Atmospheric Chemistry and Physics |
| Online Access: | https://acp.copernicus.org/articles/23/10751/2023/acp-23-10751-2023.pdf |
| Summary: | <p>Tropospheric ozone (O<span class="inline-formula"><sub>3</sub></span>) is an important surface pollutant in urban areas, and it has complex formation mechanisms that depend on the atmospheric chemistry and on meteorological factors. The severe reductions observed in anthropogenic emissions during the COVID-19 pandemic can further our understanding of the photochemical mechanisms leading to O<span class="inline-formula"><sub>3</sub></span> formation and provide guidance for policies aimed at reducing air pollution. In this study, we use the Weather Research and Forecasting model with Chemistry (WRF-Chem) coupled with the urban canopy building effect parameterization and building energy model (BEP <span class="inline-formula">+</span> BEM) to investigate changes in the ozone chemistry over the metropolitan area of Barcelona (AMB) and its atmospheric plume moving northwards, which is responsible for the highest number of hourly O<span class="inline-formula"><sub>3</sub></span> exceedances in Spain. The trajectories of the air masses from the AMB to the Pyrenees are studied with the Lagrangian FLEXible PARTicle dispersion model with WRF (FLEXPART-WRF). The aim is to investigate the response of ozone chemistry to reduction in precursor emissions (NO<span class="inline-formula"><sub><i>x</i></sub></span> – nitrogen oxides; VOCs – volatile organic compounds). The results show that, with the reduction in emissions, (1) the ozone chemistry tends to enter the NO<span class="inline-formula"><sub><i>x</i></sub></span>-limited or transition regimes, but highly polluted urban areas are still in the VOC-limited regime; (2) the reduced O<span class="inline-formula"><sub>3</sub></span> production is overwhelmed by reduced nitric oxide (NO) titration, resulting in a net increase in the O<span class="inline-formula"><sub>3</sub></span> concentration (up to 20 %) in the evening; (3) the increase in the maximum O<span class="inline-formula"><sub>3</sub></span> level (up to 6 %) during the highest emission-reduction period could be attributed to an enhancement in the atmospheric oxidants hydroxyl and nitrate radical (OH and NO<span class="inline-formula"><sub>3</sub></span>) given their strong link with O<span class="inline-formula"><sub>3</sub></span> loss or production chemistry; (4) the daily maximum levels of ozone and odd oxygen species (O<span class="inline-formula"><sub><i>x</i></sub></span>) generally decreased (4 %) in May – a period with intense radiation which favours ozone production – with the reduced atmospheric OH and NO<span class="inline-formula"><sub>3</sub></span> oxidants, indicating an improvement in the air quality; and (5) ozone precursor concentration changes in the urban plume of Barcelona contribute significantly to the level of pollution along the 150 km south-to-north valley in the Pyrenees. Our results indicate that O<span class="inline-formula"><sub>3</sub></span> abatement strategies cannot rely only on NO<span class="inline-formula"><sub><i>x</i></sub></span> emission control but must include a significant reduction in anthropogenic sources of VOCs. In addition, our results show that mitigation strategies intended to reduce O<span class="inline-formula"><sub>3</sub></span> should be designed according to the local meteorology, air transport, particular ozone regimes, and oxidation capacity of the atmosphere of the urban area.</p> |
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| ISSN: | 1680-7316 1680-7324 |