Abstract
Abstract. Nitrogen-containing organic compounds, which may be directly emitted into the atmosphere or which 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 2018 Long Island Sound Tropospheric Ozone Study – LISTOS – 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. We observed a range of functionalized compounds containing oxygen, nitrogen, and/or sulfur atoms resulting from these direct emissions and chemical transformations, including photochemical and aqueous-phase processing that was more pronounced in summer and winter, respectively. 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 % and 68 % of total measured ion 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). Reduced nitrogen functional groups observed in the particle phase were frequently paired with oxygen-containing groups elsewhere on the molecule, and their prevalence 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 US and potentially in other regions with similar anthropogenic, biogenic, and marine source signatures.
Highlights
Coastal regions near the Long Island Sound often experience poor air quality due to a combination of biogenic and anthropogenic emissions from upwind metropolitan areas along the East Coast of the US
We discuss three types of sampling and quadrupole timeof-flight mass spectrometry-based analyses here: particles collected on Teflon filters and analyzed using liquid chromatography with electrospray ionization, gases collected on packed adsorbent tubes and analyzed using gas chromatography with atmospheric pressure chemical ionization, and functionalized gases collected on cooled polyether ether ketone (PEEK) samplers and analyzed using liquid chromatography with electrospray ionization
While our correlations and conclusions are somewhat limited by the 8 h filter sampling duration and the resulting highly regionally mixed samples, one possible hypothesis is that the presence of nitrogen oxides (NOx) could have promoted more fragmentation reactions in the gas phase (Loza et al, 2014) that decreased average carbon number and correspondingly increased volatility and O/C
Summary
Ditto et al.: Nitrogen-containing organic compounds at a coastal site but significant fraction of particulate matter with a diameter of 2.5 μm or less (i.e., PM2.5). Both O3 and PM2.5 are of particular concern for human health and climate; O3 is known to cause an increase in respiratory-related illnesses (Di et al, 2017; Jerrett et al, 2009), while PM2.5 is known to cause adverse cardiovascular, respiratory, and cognitive effects and to impact climate forcings (Di et al, 2017; Hallquist et al, 2009; Kilian and Kitazawa, 2018; Pope and Dockery, 2006). Coupled with local emissions and chemistry, these incoming aged air parcels from coastal metropolitan areas contribute to the Long Island Sound region often entering nonattainment for O3 (United States Environmental Protection Agency, 2020), especially in the summer
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