Seasonal Analysis of Reduced and Oxidized Nitrogen-Containing Organic Compounds at a Coastal Site

Abstract

Abstract. Nitrogen-containing organic compounds, which may be directly emitted to the atmosphere or may form via reactions with prevalent reactive nitrogen species (e.g. NH3, NOx, NO3), have important but uncertain effects on climate and human health. Using gas and liquid chromatography with soft ionization and high-resolution mass spectrometry, we performed a molecular-level speciation of functionalized organic compounds at a coastal site on the Long Island Sound in summer (during the LISTOS 2018 campaign) and winter. This region often experiences poor air quality due to the emissions of reactive anthropogenic, biogenic, and marine-derived compounds and their chemical transformation products. Indeed, we observed a range of functionalized compounds containing oxygen, nitrogen, and/or sulfur atoms resulting from a mix of direct emissions and chemical transformations, including photochemical processing in summer and aqueous-phase processing in winter. In both summer and winter, nitrogen-containing organic aerosols dominated the observed distribution of functionalized particle-phase species ionized by our analytical techniques, with 85\u2009% and 68\u2009% of measured compound abundance containing a nitrogen atom, respectively. Nitrogen-containing particles included reduced nitrogen functional groups (e.g. amines, imines, azoles) and common NOz contributors (e.g. organonitrates). The prevalence of reduced nitrogen functional groups observed in the particle-phase, while frequently paired with oxygen-containing groups elsewhere on the molecule, often rivaled that of oxidized nitrogen groups detected by our methods. Supplemental gas-phase measurements, collected on adsorptive samplers and analyzed with a novel liquid chromatography-based method, suggest that gas-phase reduced nitrogen compounds are possible contributing precursors to the observed nitrogen-containing particles. Altogether, this work highlights the prevalence of reduced nitrogen-containing compounds in the less-studied Northeastern U.S., and potentially in other regions with similar anthropogenic, biogenic, and marine source signatures.\n