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- Title
Particulate Nitrate Photolysis as a Possible Driver of Rising Tropospheric Ozone.
- Authors
Shah, Viral; Keller, Christoph A.; Knowland, K. Emma; Christiansen, Amy; Hu, Lu; Wang, Haolin; Lu, Xiao; Alexander, Becky; Jacob, Daniel J.
- Abstract
Tropospheric ozone is an air pollutant and a greenhouse gas whose anthropogenic production is limited principally by the supply of nitrogen oxides (NOx) from combustion. Tropospheric ozone in the northern hemisphere has been rising despite the flattening of NOx emissions in recent decades. Here we propose that this sustained increase could result from the photolysis of nitrate particles (pNO3−) to regenerate NOx. Including pNO3− photolysis in the GEOS‐Chem atmospheric chemistry model improves the consistency with ozone observations. Our simulations show that pNO3− concentrations have increased since the 1960s because of rising ammonia and falling SO2 emissions, augmenting the increase in ozone in the northern extratropics by about 50% to better match the observed ozone trend. pNO3− will likely continue to increase through 2050, which would drive a continued increase in ozone even as NOx emissions decrease. More work is needed to better understand the mechanism and rates of pNO3− photolysis. Plain Language Summary: In the troposphere, ozone is an air pollutant and a greenhouse gas. Tropospheric ozone forms from reactions involving carbon monoxide and volatile organic compounds in the presence of nitrogen oxides. Global emissions of nitrogen oxides have been leveling off in the past few decades, yet tropospheric ozone levels have kept on rising. We propose that this rise in ozone could be driven by a growing source of nitrogen oxides from the photolysis of nitrate particles, which have become more abundant due to falling sulfur dioxide and rising ammonia emissions. We find that including nitrate particle photolysis in an atmospheric chemistry model improves its consistency with the observed ozone distribution and trends. Our results point to the importance of considering nitrate particle photolysis for future projections of climate forcing from tropospheric ozone, and the need for further work to reduce the uncertainty in the mechanism and rates of the process. Key Points: Particulate nitrate photolysis improves the consistency of tropospheric ozone in the GEOS‐Chem model with observationsIncrease in particulate nitrate due to falling SO2 and rising NH3 emissions could augment the long‐term increase in tropospheric ozoneBetter characterization of the mechanism and rates of particulate nitrate photolysis is needed
- Subjects
TROPOSPHERIC ozone; PARTICULATE nitrate; AIR pollutants; ORGANONITROGEN compounds; PHOTOLYSIS (Chemistry); OZONE
- Publication
Geophysical Research Letters, 2024, Vol 51, Issue 5, p1
- ISSN
0094-8276
- Publication type
Article
- DOI
10.1029/2023GL107980