10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
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Measurement of Speciated Gaseous and Particulate Organic Nitrates in Urban Atlanta using FIGAERO-HR-ToF-I-CIMS
MASAYUKI TAKEUCHI, Gamze Eris, Taekyu Joo, Yunle Chen, Weiqi Xu, Dao Huang, Gabriela Saavedra, Seongshik Kim, Dong Gao, Rodney J. Weber, Yele Sun, Michael Walker, Brent Williams, Jenna Ditto, Drew Gentner, David Tanner, Greg Huey, Nga Lee Ng, Georgia Institute of Technology
Abstract Number: 1034 Working Group: Carbonaceous Aerosol
Abstract Owing to the semi-/low-volatile nature of organic nitrates and their implication for the budget of reactive nitrogen species (i.e. NOx) and ozone formation, atmospheric organic nitrates have been receiving increased attention in the atmospheric research community. Previous field studies using online instruments, such as Thermal-Dissociation Laser-Induced Fluorescence (TD-LIF) and Aerosol Mass Spectrometer (AMS), have demonstrated the ubiquitous presence of organic nitrates across different continents and in different environments. However, there is limited understanding at the molecular level of such organic nitrate species and the seasonal effect on their chemical composition. Additionally, the dominant source (e.g. daytime vs. nighttime, primary vs. secondary, etc.) and the fate of organic nitrates are not well understood. In this study, the Filter Inlet for Gases and AEROsols (FIGAERO) coupled to High Resolution Time-of-Flight Iodide Chemical Ionization Mass Spectrometer (HR-ToF-I-CIMS) was used to measure speciated gaseous and submicron particulate organic nitrates at the Jefferson Street site in Atlanta, GA, USA which is an urban site in the Southeastern Aerosol Research and Characterization (SEARCH) network, using. Measurements were conducted in summer 2017 and winter 2018. Preliminary results show that C4-5 and C8-10 organic nitrates represent a significant fraction of total organic nitrates in summer, suggesting the important role of biogenic volatile organic compounds such as isoprene and monoterpenes. However, C8-10 organic nitrate species dominates over C4-5 organic nitrates in winter due to reduced isoprene emission. In addition, we observed high molecular weight compounds, tentatively assigned as C20 organic mono-/di-nitrates, in the particle-phase that exhibit a clear diurnal pattern peaking little after midnight. These high molecular weight compounds are also detected in laboratory chamber experiments of monoterpene NO3 oxidation, implying a significant contribution of NO3 chemistry to the formation of particulate organic nitrates in winter. Bulk volatility distributions of ambient organic nitrates derived from FIGAERO thermogram data are presented and compared with those of laboratory-generated organic nitrate aerosols to confirm the contribution of NO3 oxidation to organic nitrate aerosol formation. Lastly, the effects of ambient temperature, relative humidity, NOx level, and the level of various volatile organic compounds on the ambient concentrations of speciated and bulk organic nitrates will be discussed.