Global nitrous acid emissions and levels of regional oxidants enhanced by wildfires
De Smedt, I.
Knote, C, Yu, H.
Van Roozendael, M.
Earth and related Environmental sciences
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Nitrous acid (HONO) is a precursor of the hydroxyl radical in the atmosphere, which controls the degradation of greenhouse gases, contributes to photochemical smog and ozone production, and influences air quality. Although biomass burning is known to contribute substantially to global aerosols and reactive gas emissions, pyrogenic contributions to HONO emissions are poorly constrained and often omitted in models. Here we present a global survey of TROPOMI/Sentinel-5 Precursor satellite sounder observations and show that HONO emissions are consistently enhanced in fresh wildfire plumes. Comparing major ecosystems (savanna, grassland, shrubland and tropical and extratropical forests), we found that the enhancement ratios of HONO to nitrogen dioxide varied systematically with biome type, with the lowest in savannas and grasslands and highest in extratropical evergreen forests. Supported by airborne measurements, we demonstrate that previous assessments underestimate pyrogenic HONO emissions by a factor of 2–4 across all ecosystem types. We estimate that HONO emissions are responsible for two-thirds of the hydroxyl radical production in fresh wildfire plumes worldwide and act to accelerate oxidative plume chemistry and ozone production. Our findings suggest that pyrogenic HONO emissions have a substantial impact on atmospheric composition, which enhances regional ozone levels by up to 7 ppbv.
CitationTheys, N.; Volkamer, R.; Müller, J.-F.; Zarzana, K.J.; Kille, N.; Clarisse, L.; De Smedt, I.; Lerot, C.; Finkenzeller, H.; Hendrick, F.; Koenig, T.K.; Lee, C.F.; Knote, C, Yu, H.; Van Roozendael, M. (2020). Global nitrous acid emissions and levels of regional oxidants enhanced by wildfires. , Nature Geoscience, Vol. 13, Issue 10, 681-686, DOI: 10.1038/s41561-020-0637-7.