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Predictions of wildfire emissions of HONO remain challenging
Wildfires pose a growing problem at the global scale. Emissions of gases and aerosols by fires severely affect air quality and climate. In the past years, increasing attention has been paid to nitrous acid, a constituent emitted by fires which is believed to be important in the reactive chemistry in smoke plumes, that leads to the formation of ozone and aerosols.
However, accurate predictions of wildfire emissions of HONO remain challenging on regional and global scales, and the chemical processes involving HONO in wildfires are uncertain.
Recent HONO measurements from space in fresh biomass burning plumes by TROPOMI (Theys et al., 2020) offer the potential to inform about HONO formation mechanisms globally.
What is the potential of current and future space sensors to measure HONO?
There is a pressing need to further develop, interpret and evaluate HONO retrievals from space observations, especially with the advent of new space instruments on geostationary platforms.
BIRA-IASB, in collaboration with the Université Libre de Bruxelles (ULB), has worked on demonstrating the detection of HONO from multiple satellite instruments (TROPOMI, GEMS and IASI) using highly sensitive retrieval techniques.
The TROPOMI retrievals were evaluated against HONO columns measured by IASI and independent estimates from the BB-FLUX aircraft campaign in 2018 over the western US. We highlighted the importance of accounting for the effect of aerosols on the sensitivity of the TROPOMI instrument.
The example below shows TROPOMI detection of HONO from two fires during the Los Angeles crisis in January 2025.
We have also reported, for the first time, the detection of HONO from geostationary UV-visible observations, by applying the TROPOMI HONO algorithm to the data from the Korean GEMS sensor, covering the region of Southeast Asia.
For the March-April 2021 burning season, enhanced HONO columns were found in countries like Laos and Myanmar, at locations where agricultural and forest fires are known to occur. The temporally resolved HONO observations from GEMS revealed that the detection of HONO is highly variable during the day, but that it largely follows the diurnal variation of the fire radiative power.
The satellite HONO datasets are publicly available on the BIRA-IASB HONO webpage.
References
- Franco, B., Clarisse, L., Theys, N., Hadji-Lazaro, J., Clerbaux, C., and Coheur, P.: Pyrogenic HONO seen from space: insights from global IASI observations, Atmos. Chem. Phys., 24, 4973–5007, https://doi.org/10.5194/acp-24-4973-2024, 2024.
- Theys, N., R. Volkamer, J.-F. Müller, K. J. Zarzana, N. Kille, L. Clarisse, I. De Smedt, C. Lerot, H. Finkenzeller, F. Hendrick, T. K. Koenig, C. F. Lee, C. Knote, H. Yu, and M. Van Roozendael: Global nitrous acid emissions and levels of regional oxidants enhanced by wildfires, Nat. Geosci., 13, 681-686 (2020). https://doi.org/10.1038/s41561-020-0637-7
