Abstract View
Observations of Oxidized and Reduced Nitrogen-Containing Gases and Particles via Liquid Chromatography at a Coastal Downwind Site Demonstrate the Prevalence of Reduced Nitrogen Molecular Features
DREW GENTNER, Jenna Ditto, Jo Machesky, Yale University
Abstract Number: 504
Working Group: Aerosol Chemistry
Abstract
Reactive nitrogen compounds play key roles in atmospheric organic chemistry through reactions of organic compounds (e.g. volatile organic compounds) with NOX (NO and NO2), nitrate radicals (NO3), and other oxidized nitrogen species, yielding a wide range of products with oxidized nitrogen-containing functional groups (i.e. NOZ). Additionally, compounds containing reduced nitrogen are emitted from anthropogenic and biogenic sources (incl. biomass burning) and their secondary formation has been observed via reactions with ammonia (or small amines). Using multi-season measurements from a coastal site downwind from several major urban areas on the Long Island Sound in Connecticut, we observe a diverse array of multifunctional nitrogen-containing organic compounds in the gas and particle phase, and elevated levels of nitrogen-containing organic aerosols compared to other sites.
The functional groups comprising these nitrogenated organic aerosols were determined via offline liquid chromatography with electrospray ionization (LC-ESI) and high-resolution tandem mass spectrometry, and included reduced nitrogen groups (e.g. amines, imines, nitriles) present in both acyclic and cyclic structures, as well as functional groups commonly found in NOZ species (e.g. organonitrates). While these nitrogenated compounds very often included oxygen atoms, the oxygen atoms were frequently independent of the reduced nitrogen functional groups and instead part of other oxygen-containing structures (hydroxyls, etc.). In the particle phase LC-ESI measurements, the prevalence of reduced nitrogen functional groups often rivaled that of oxidized nitrogen groups. In the summer, reduced nitrogen groups contributed to half of compounds with an O/N ratio < 3 and two-thirds of compounds with an O/N ratio ≥ 3, and in the winter they contributed to half and only one-eighth, respectively. Supplemental gas-phase measurements via LC-ESI indicates the presence of gas-phase reduced nitrogen compounds as possible precursors to particle-phase compounds containing nitrogen and oxygen. In all, this work highlights the prevalence of reduced nitrogen molecular features in oxygen- and nitrogen-containing compounds beyond typical NOZ species, including those that may be the result of aqueous-phase chemistry (e.g. azoles), and provides a detailed molecular-level analysis of functionalized organic compounds in the less-studied Northeastern U.S.