Does the Conversion of Biogenic Organic Nitrates to Nitric Acid Control the Lifetime of Atmospheric Nitrogen Oxides Over the Eastern U.S.?

Abstract

Airborne measurements over the Southeast US during the summer of 2013 revealed the evolution of nitrogen oxides and nitric acid that was markedly different from that over the Northeast US during the winter of 2015. We can reconcile the observed trends by invoking nitrogen oxide reservoir species formed under elevated NO _x environments that then convert to HNO ₃ . This process may represent a daytime loss pathway of NO _x that is faster by many factors than the oxidation of nitrogen dioxide by hydroxyl radicals. We present measurements of a suite of organic nitrates made using online iodide‐ionization time‐of‐flight mass spectrometry and simple box modeling that support their role in controlling the net conversion of NO _x to HNO ₃ . Rapid loss of organic nitrates derived from biogenic volatile organic compounds, such as what we infer from this analysis, has significant implications for our understanding of oxidant budgets and top‐down NO _x emissions assessments.