High urban NO<i><sub>x</sub></i> triggers a substantial chemical downward flux of ozone.
other · Level V
Where this comes from
- Record sourced from PubMed, PMID 36652521.
- Also identified by DOI 10.1126/sciadv.add2365 and PMC identifier 9848777.
- Licence recorded as CC BY.
- The licence permits redistribution, so the abstract is shown in full and the full text is available from the publisher.
Abstract
Nitrogen oxides (NO<i><sub>x</sub></i>) play a central role in catalyzing tropospheric ozone formation. Nitrogen dioxide (NO<sub>2</sub>) has recently reemerged as a key target for air pollution control measures, and observational evidence points toward a limited understanding of ozone in high-NO<i><sub>x</sub></i> environments. A complete understanding of the mechanisms controlling the rapid atmospheric cycling between ozone (O<sub>3</sub>)-nitric oxide (NO)-NO<sub>2</sub> in high-NO<i><sub>x</sub></i> regimes at the surface is therefore paramount but remains challenging because of competing dynamical and chemical effects. Here, we present long-term eddy covariance measurements of O<sub>3</sub>, NO, and NO<sub>2</sub>, over an urban area, that allow disentangling important physical and chemical processes. When generalized, our findings suggest that the depositional O<sub>3</sub> flux near the surface in urban environments is negligible compared to the flux caused by chemical conversion of O<sub>3</sub>. This leads to an underestimation of the Leighton ratio and is a key process for modulating urban NO<sub>2</sub> mixing ratios. As a consequence, primary NO<sub>2</sub> emissions have been significantly overestimated.