A nitrate photolysis source of tropospheric HONO is incompatible with current understanding of atmospheric chemistry
Year: 2025
Type: article
Abstract: . Recent observations of nitrous acid (HONO) in the remote troposphere found much higher concentrations than can be explained through known sources, with important implications for air quality and climate. Laboratory evidence and modelling of field observations suggests that nitrate aerosol photolysis is the likely mechanism providing the additional HONO, offering a rapid route for recycling of NOx from nitric acid (HNO3). Previous studies of the global impact of this chemistry have used either very restricted HONO data or a “top-down” approach to parameterize the HONO source by reconciling simulated and observed NOx concentrations. Here, we use multiple, independent tropospheric HONO observations from different locations to parameterize nitrate photolysis, and evaluate its impacts on global atmospheric chemistry using GEOS-Chem. The simulations improve agreement between modelled and observed HONO concentrations relative to previous studies, decreasing the model bias by 5–20 %. The remaining (and large) underestimate of HONO in the model is due predominantly to an underestimate of total nitrate aerosol (-95 %) and is reduced to 20 % when accounting for low model nitrate. Despite the low bias in the model HONO, we find that nitrate aerosol photolysis leads to substantial global increases in NOx, O3 and OH concentrations, likely beyond the observational constraints. The additional source of NOx (~48 Tg N yr-1 globally) is comparable to total NOx emissions from all sources (~55 Tg yr-1). These HONO observations in the remote troposphere, thus imply a large uncertainty in the NOx budget and an incomplete understanding of atmospheric chemistry.
Authors: Matthew J. Rowlinson, Lucy J. Carpenter, Mat J. Evans, James D. Lee, Simone T. Andersen, Tomas Sherwen, Anna B. Callaghan, Roberto Sommariva, William Bloss, Siqi Hou, Leigh R. Crilley, Klaus Pfeilsticker, Benjamin Weyland, Thomas B. Ryerson, Patrick R. Veres, Pedro Campuzano-Jost, Hongyu Guo, Benjamin A. Nault, Jose L. Jimenez, Khanneh Wadinga Fomba
Institutions: National Centre for Atmospheric Science, University of York, Max Planck Institute for Chemistry, University of Birmingham, Heidelberg University, National Oceanic and Atmospheric Administration, NOAA Chemical Sciences Laboratory, NSF National Center for Atmospheric Research, NOAA Earth System Research Laboratory, Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Johns Hopkins University, Aerodyne Research, Langley Research Center, Leibniz Institute for Tropospheric Research
Language: English
Subfield: Atmospheric Science
Field: Earth and Planetary Sciences
Domain: Physical Sciences
SDG: Climate action
Open Access status: gold
Estimated APC paid: $1,725
Awards: G129503900, G1515677456, G1517700047, Atmospheric reactive nitrogen cycling over the ocean, G1938022960, G2115564622, G2889253305, G3004607768, G414971594, G451167019, SEANA -Shipping Emissions in the Arctic and North Atlantic atmosphere, SEANA -Shipping Emissions in the Arctic and North Atlantic atmosphere, G522860791, G529052362, G5540027230, G6547476290, Resolving climate sensitivity associated with shallow mixed phase cloud in the oceanic mid- to high-latitudes (M-Phase), G8585165044
OpenAlex ID: W4416771407