Search Results
Secondary organic aerosol (SOA) yields from NO3 radical + isoprene based on nighttime aircraft power plant plume transects
2018, Fry, Juliane L., Brown, Steven S., Middlebrook, Ann M., Edwards, Peter M., Campuzano-Jost, Pedro, Day, Douglas A., Jimenez, José L., Allen, Hannah M., Ryerson, Thomas B., Pollack, Ilana, Graus, Martin, Warneke, Carsten, de Gouw, Joost A., Brock, Charles A., Gilman, Jessica, Lerner, Brian M., Dubé, William P., Liao, Jin, Welti, André
Nighttime reaction of nitrate radicals (NO3) with biogenic volatile organic compounds (BVOC) has been proposed as a potentially important but also highly uncertain source of secondary organic aerosol (SOA). The southeastern United States has both high BVOC and nitrogen oxide (NOx) emissions, resulting in a large model-predicted NO3-BVOC source of SOA. Coal-fired power plants in this region constitute substantial NOx emissions point sources into a nighttime atmosphere characterized by high regionally widespread concentrations of isoprene. In this paper, we exploit nighttime aircraft observations of these power plant plumes, in which NO3 radicals rapidly remove isoprene, to obtain field-based estimates of the secondary organic aerosol yield from NO3 + isoprene. Observed in-plume increases in nitrate aerosol are consistent with organic nitrate aerosol production from NO3 + isoprene, and these are used to determine molar SOA yields, for which the average over nine plumes is 9 % (±5 %). Corresponding mass yields depend on the assumed molecular formula for isoprene-NO3-SOA, but the average over nine plumes is 27 % (±14 %), on average larger than those previously measured in chamber studies (12 %-14 % mass yield as ΔOA / ΔVOC after oxidation of both double bonds). Yields are larger for longer plume ages. This suggests that ambient aging processes lead more effectively to condensable material than typical chamber conditions allow. We discuss potential mechanistic explanations for this difference, including longer ambient peroxy radical lifetimes and heterogeneous reactions of NO3-isoprene gas phase products. More in-depth studies are needed to better understand the aerosol yield and oxidation mechanism of NO3 radical + isoprene, a coupled anthropogenic-biogenic source of SOA that may be regionally significant.
No Evidence for a Significant Impact of Heterogeneous Chemistry on Radical Concentrations in the North China Plain in Summer 2014
2020, Tan, Zhaofeng, Hofzumahaus, Andreas, Lu, Keding, Brown, Steven S., Holland, Frank, Huey, Lewis Gregory, Kiendler-Scharr, Astrid, Li, Xin, Liu, Xiaoxi, Ma, Nan, Min, Kyung-Eun, Rohrer, Franz, Shao, Min, Wahner, Andreas, Wang, Yuhang, Wiedensohler, Alfred, Wu, Yusheng, Wu, Zhijun, Zeng, Limin, Zhang, Yuanhang, Fuchs, Hendrik
The oxidation of nitric oxide to nitrogen dioxide by hydroperoxy (HO2) and organic peroxy radicals (RO2) is responsible for the chemical net ozone production in the troposphere and for the regeneration of hydroxyl radicals, the most important oxidant in the atmosphere. In Summer 2014, a field campaign was conducted in the North China Plain, where increasingly severe ozone pollution has been experienced in the last years. Chemical conditions in the campaign were representative for this area. Radical and trace gas concentrations were measured, allowing for calculating the turnover rates of gas-phase radical reactions. Therefore, the importance of heterogeneous HO2 uptake on aerosol could be experimentally determined. HO2 uptake could have suppressed ozone formation at that time because of the competition with gas-phase reactions that produce ozone. The successful reduction of the aerosol load in the North China Plain in the last years could have led to a significant decrease of HO2 loss on particles, so that ozone-forming reactions could have gained importance in the last years. However, the analysis of the measured radical budget in this campaign shows that HO2 aerosol uptake did not impact radical chemistry for chemical conditions in 2014. Therefore, reduced HO2 uptake on aerosol since then is likely not the reason for the increasing number of ozone pollution events in the North China Plain, contradicting conclusions made from model calculations reported in the literature. © 2020 American Chemical Society.
Nitrate radicals and biogenic volatile organic compounds: Oxidation, mechanisms, and organic aerosol
2017, Ng, Nga Lee, Brown, Steven S., Archibald, Alexander T., Atlas, Elliot, Cohen, Ronald C., Crowley, John N., Day, Douglas A., Donahue, Neil M., Fry, Juliane L., Fuchs, Hendrik, Griffin, Robert J., Guzman, Marcelo I., Herrmann, Hartmut, Hodzic, Alma, Iinuma, Yoshiteru, Jimenez, José L., Kiendler-Scharr, Astrid, Lee, Ben H., Luecken, Deborah J., Mao, Jingqiu, McLaren, Robert, Mutzel, Anke, Osthoff, Hans D., Ouyang, Bin, Picquet-Varrault, Benedicte, Platt, Ulrich, Pye, Havala O.T., Rudich, Yinon, Schwantes, Rebecca H., Shiraiwa, Manabu, Stutz, Jochen, Thornton, Joel A., Tilgner, Andreas, Williams, Brent J., Zaveri, Rahul A.
Oxidation of biogenic volatile organic compounds (BVOC) by the nitrate radical (NO3) represents one of the important interactions between anthropogenic emissions related to combustion and natural emissions from the biosphere. This interaction has been recognized for more than 3 decades, during which time a large body of research has emerged from laboratory, field, and modeling studies. NO3-BVOC reactions influence air quality, climate and visibility through regional and global budgets for reactive nitrogen (particularly organic nitrates), ozone, and organic aerosol. Despite its long history of research and the significance of this topic in atmospheric chemistry, a number of important uncertainties remain. These include an incomplete understanding of the rates, mechanisms, and organic aerosol yields for NO3-BVOC reactions, lack of constraints on the role of heterogeneous oxidative processes associated with the NO3 radical, the difficulty of characterizing the spatial distributions of BVOC and NO3 within the poorly mixed nocturnal atmosphere, and the challenge of constructing appropriate boundary layer schemes and non-photochemical mechanisms for use in state-of-the-art chemical transport and chemistry–climate models. This review is the result of a workshop of the same title held at the Georgia Institute of Technology in June 2015. The first half of the review summarizes the current literature on NO3-BVOC chemistry, with a particular focus on recent advances in instrumentation and models, and in organic nitrate and secondary organic aerosol (SOA) formation chemistry. Building on this current understanding, the second half of the review outlines impacts of NO3-BVOC chemistry on air quality and climate, and suggests critical research needs to better constrain this interaction to improve the predictive capabilities of atmospheric models.