Nitrogenous air pollutants at a southern California mountain forest smog receptor site |
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| Institution: | 1. Department of Chemistry, Bielefeld University, Universitätsstraße 25, D-33615 Bielefeld, Germany;2. Physico-Chemical Fundamentals of Combustion, RWTH Aachen University, Schinkelstraße 8, D-52062 Aachen, Germany;3. Department of Mechanical Engineering, Stanford University, 450 Serra Mall, Stanford, CA 94305-3032, USA;1. School of Automation, University of Electronic Science and Technology of China, Chengdu 610054, Sichuan, PR China;2. Geographical and Sustainability Sciences Department, University of Iowa, Iowa City, IA 52242, USA;3. School of Foreign Languages, Sichuan Normal University, Chengdu 610101, PR China;2. Faculty of Science, Taif University, Taif, Kingdom of Saudi Arabia;3. Faculty of Science, Alexandria University, Alexandria, Egypt;4. Faculty of Science, Port Said University, Port Said, Egypt |
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| Abstract: | Ambient levels of the nitrogenous pollutants NO, NO2, nitric acid, nitrous acid, ammonia, particulate nitrate, particulate ammonium, peroxyacetyl nitrate (PAN) and peroxypropionyl nitrate (PPN) have been measured at a southern California mountain forest location severely impacted by urban photochemical smog. Air quality at the mountain forest location was characterized by high levels of nitric acid (up to 18 ppb) and the phytotoxic peroxyacyl nitrates PAN (up to 22 ppb) and PPN (up to 5 ppb). Alkyl nitrates were below our detection limits of 0.05–0.5 ppb. The (PAN + PPN)/NO2 ratios varied substantially (range 0.03–2.27) and were generally large, with typical 24-h averages of 0.19–0.50. Diurnal variations of the (PAN/PPN)/NO2 ratio exhibited both nighttime and daytime maxima reflecting diurnal variations in PAN (and PPN) thermal stability and photochemical production rates, respectively. Organic nitrogen-containing oxidation products (PAN + PPN) were more abundant than inorganic nitrate (HNO3 + NO3−), with an average organic/inorganic concentration ratio of 2.5 (daytime ratio 1.0; nighttime ratio 3.7). The four oxidation products PAN, PPN, HNO3 and NO3− together accounted for 0.26 of the total reactive nitrogen. The results are discussed with respect to diurnal and seasonal variations and in terms of NO2 atmospheric oxidation pathways. Deposition fluxes and velocities to ponderosa pine have been measured for inorganic nitrate and for ammonium and have been compared with those obtained at other mountain forest locations. |
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