Poorly quantified trends in ammonium nitrate remain critical to understand future urban aerosol control strategies.
basic_science · Level V
Where this comes from
- Record sourced from PubMed, PMID 40397739.
- Also identified by DOI 10.1126/sciadv.adt8957 and PMC identifier 12094242.
- 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
Despite decades of progress in reducing nitrogen oxide (NO<i><sub>x</sub></i>) emissions, ammonium nitrate (AN) remains the primary inorganic component of particulate matter (PM) in Los Angeles (LA). Using aerosol mass spectrometry over multiple years in LA illustrates the controlling dynamics of AN and their evolution over the past decades. These data suggest that much of the nitric acid (HNO<sub>3</sub>) production required to produce AN in LA occurs during the nighttime via heterogeneous hydrolysis of N<sub>2</sub>O<sub>5</sub>. Further, we show that US Environmental Protection Agency-codified techniques for measuring total PM<sub>2.5</sub> fail to quantify the AN component, while low-cost optical sensors demonstrate good agreement. While previous studies suggest that declining NO<i><sub>x</sub></i> has reduced AN, we show that HNO<sub>3</sub> formation is still substantial and leads to the formation of many tens of micrograms per cubic meter of AN aerosol. Continued focus on reductions in NO<i><sub>x</sub></i> will help meet the PM<sub>2.5</sub> standards in the LA basin and many other regions.