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Environmental Chamber Studies of Reduced Nitrogen Compounds Observed in Anthropogenic Emissions


Secondary organic aerosol (SOA) pollution has negative impacts on human health and well-being. While efforts have been made to characterize the chemical reactions leading to SOA formation, reduced nitrogen compounds remain a poorly studied class of chemicals contributing to air pollution. Sources of reduced nitrogen compounds include agricultural emissions, biomass burning, carbon capture sequestration and selective catalytic reduction control devices, low vapor pressure volatile organic compounds (LVP-VOC) found in many consumer products, and charbroiled meats. Understanding the atmospheric chemical mechanisms of reduced nitrogen compounds is important for comprehensive design of effective air pollution strategies. Therefore, this study seeks to determine the impact of reduced nitrogen compound chemistry on SOA formation. Experiments were conducted at the UCR College of Engineering – Center for Environmental Research and Technology (CE-CERT) Atmospheric Processes Laboratory. This facility houses several well characterized indoor environmental chambers, which allow for the study of atmospheric processes under controlled conditions. Chamber experiments consisted of a reduced nitrogen compound being reacted with atmospheric oxidants including hydroxyl radical (OH) and nitrate radical (NO3). The chemical composition of the gas and aerosol species were determined through mass spectrometry techniques. The physical properties of the aerosol, including density, volatility, and hygroscopicity, as well as particle concentration and size distribution were measured with a variety of house built particle mobility analyzers. A suite of gas analyzers were used to measure Ozone, NOx, and CO concentrations. Experiments with primary, secondary, and tertiary aliphatic amines have provided insights into previously undiscovered reaction mechanisms. Aqueous phase acid catalyzed aldol addition/condensation reactions were observed in secondary amine experiments under humid conditions. Carcinogenic nitramines were observed in secondary amine reactions with nitrate radical. Longer chain secondary amines formed less dense aerosol, suggesting the formation of fractal shaped particles. The discovery of oligomer formation in the reaction of amines with methyl functional groups (dimethylamine, trimethylamine, 2-dimethylaminoethanol) with atmospheric radicals has important implications for SOA formation in areas with high concentrations of amine emissions. Meteorological factors including humidity and temperature played an important role in the reaction chemistry of reduced nitrogen compounds. Humidity provided additional, aqueous phase, reaction pathways. Temperature had an effect on gas to particle partitioning, particularly with the amine salts. The concentration of aerosol formed during radical oxidation of amino alcohols has implications on the use of these compounds in carbon capture sequestration control devices.

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