Browsing by Subject "REACTIVE UPTAKE"

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  • D'Ambro, Emma L.; Schobesberger, Siegfried; Gaston, Cassandra J.; Lopez-Hilfiker, Felipe D.; Lee, Ben H.; Liu, Jiumeng; Zelenyuk, Alla; Bell, David; Cappa, Christopher D.; Helgestad, Taylor; Li, Ziyue; Guenther, Alex; Wang, Jian; Wise, Matthew; Caylor, Ryan; Surratt, Jason D.; Riedel, Theran; Hyttinen, Noora; Salo, Vili-Taneli; Hasan, Galib; Kurten, Theo; Shilling, John E.; Thornton, Joel A. (2019)
    We present measurements utilizing the Filter Inlet for Gases and Aerosols (FIGAERO) applied to chamber measurements of isoprene-derived epoxydiol (IEPOX) reactive uptake to aqueous acidic particles and associated secondary organic aerosol (SOA) formation. Similar to recent field observations with the same instrument, we detect two molecular components desorbing from the IEPOX SOA in high abundance: C5H12O4 and C5H10O3. The thermal desorption signal of the former, presumably 2-methyltetrols, exhibits two distinct maxima, suggesting it arises from at least two different SOA components with significantly different effective volatilities. Isothermal evaporation experiments illustrate that the most abundant component giving rise to C5H12O4 is semi-volatile, undergoing nearly complete evaporation within 1 h while the second, less volatile component remains unperturbed and even increases in abundance. We thus confirm, using controlled laboratory studies, recent analyses of ambient SOA measurements showing that IEPOX SOA is of very low volatility and commonly measured IEPOX SOA tracers such as C5H12O4 and C5H10O3, presumably 2-methyltetrols and C5-alkene triols or 3-MeTHF-3,4-diols, result predominantly from thermal decomposition in the FIGAERO-CIMS. We infer that other measurement techniques using thermal desorption or prolonged heating for analysis of SOA components may also lead to reported 2-methyltetrols and C5-alkene triols or 3-MeTHF-3,4-diol structures. We further show that IEPOX SOA volatility continues to evolve via acidity-enhanced accretion chemistry on the timescale of hours, potentially involving both 2-methyltetrols and organosulfates.
  • Riva, Matthieu; Heikkinen, Liine; Bell, David M.; Peräkylä, Otso; Zha, Qiaozhi; Rissanen, Matti; Imre, D.; Petäjä, Tuukka; Thornton, Joel; Zelenyuk, Alla; Ehn, Mikael (2019)
    Secondary organic aerosol (SOA) is known to impact both climate and air quality, yet molecular-level composition measurements remain challenging, hampering our understanding of SOA formation and evolution. Here, we reveal the importance of underestimated reaction pathways for the (trans) formation of SOA from monoterpenes, one of the largest SOA precursors globally. Utilizing mass spectrometric techniques to achieve a comprehensive characterization of molecular-level changes in the SOA, we were able to link the appearance of high-molecular weight (HMW) organic molecules to the concentration and level of neutralization of particulate sulfate. Interestingly, this oligomerization coincided with a decrease of highly oxygenated molecules (HOMs). Our findings highlight the role of particle-phase processing, and the underestimated importance of sulfate aerosol for monoterpene-SOA formation. The observations of these processes directly in the atmosphere reveal the need to account for the formation of HMW oligomers to fully understand the physicochemical properties of organic aerosol.
  • Yan, Chao; Tham, Yee Jun; Zha, Qiaozhi; Wang, Xinfeng; Xue, Likun; Dai, Jianing; Wang, Zhe; Wang, Tao (2019)
    Nitrate radical (NO3) and dinitrogen pentoxide (N2O5) play crucial roles in the nocturnal atmosphere. To quantify their impacts, we deployed a thermal-dissociation chemical ionization mass spectrometry (TD-CIMS), to measure their concentration, as well as ClNO2 at a coastal background site in the southern of China during the late autumn of 2012. Moderate levels of NO3, N2O5 and high concentration of ClNO2 were observed during the study period, indicating active NOx-O-3 chemistry in the region. Distinct features of NO3, N2O5 and ClNO2 mixing ratios were observed in different airmasses. Further analysis revealed that the N2O5 heterogeneous reaction was the dominant loss of N2O5 and NO3, which showed higher loss rate compared to that in other coastal sites. Especially, the N2O5 loss rates could reach up to 0.0139 s(-1) when airmasses went across the sea. The fast heterogeneous loss of N2O5 led to rapid NOx loss which could be comparable to the daytime process through NO2 oxidization by OH, and on the other hand, to rapid nitrate aerosol formation. In summary, our results revealed that the N2O5 hydrolysis could play significant roles in regulating the air quality by reducing NOx but forming nitrate aerosols. (C) 2019 Published by Elsevier B.V.
  • Tham, Yee Jun; Wang, Zhe; Li, Qinyi; Wang, Weihao; Wang, Xinfeng; Lu, Keding; Ma, Nan; Yan, Chao; Kecorius, Simonas; Wiedensohler, Alfred; Zhang, Yuanhang; Wang, Tao (2018)
    Heterogeneous uptake of dinitrogen pentoxide (N2O5) and production of nitryl chloride (ClNO2) are important nocturnal atmospheric processes that have significant implications for the production of secondary pollutants. However, the understanding of N2O5 uptake processes and ClNO2 production remains limited, especially in China. This study presents a field investigation of the N2O5 heterogeneous uptake coefficient (gamma (N2O5)) and ClNO2 production yield (phi) in a polluted area of northern China during the summer of 2014. The N2O5 uptake coefficient and ClNO2 yield were estimated by using the simultaneously measured ClNO2 and total nitrate in 10 selected cases, which have concurrent increases in the ClNO2 and nitrate concentrations and relatively stable environmental conditions. The determined gamma (N2O5) and phi values varied greatly, with an average of 0.022 for gamma (N2O5) (+/- 0.012, standard deviation) and 0.34 for (15 (+/- 0.28, standard deviation). The variations in gamma (N2O5) could not be fully explained by the previously derived parameterizations of N2O5 uptake that consider nitrate, chloride, and the organic coating. Heterogeneous uptake of N2O5 was found to have a strong positive dependence on the relative humidity and aerosol water content. This result suggests that the heterogeneous uptake of N2O5 in Wangdu is governed mainly by the amount of water in the aerosol, and is strongly water limited, which is different from most of the field observations in the US and Europe. The ClNO2 yield estimated from the parameterization was also overestimated comparing to that derived from the observation. The observation-derived phi showed a decreasing trend with an increasing ratio of acetonitrile to carbon monoxide, an indicator of biomass burning emissions, which suggests a possible suppressive effect on the production yield of ClNO2 in the plumes influenced by biomass burning in this region. The findings of this study illustrate the need to improve our understanding and to parameterize the key factors for gamma (N(2)O5) and phi to accurately assess photochemical and haze pollution.
  • Krechmer, Jordan E.; Groessl, Michael; Zhang, Xuan; Junninen, Heikki; Massoli, Paola; Lambe, Andrew T.; Kimmel, Joel R.; Cubison, Michael J.; Graf, Stephan; Lin, Ying-Hsuan; Budisulistiorini, Sri H.; Zhang, Haofei; Surratt, Jason D.; Knochenmuss, Richard; Jayne, John T.; Worsnop, Douglas R.; Jimenez, Jose-Luis; Canagaratna, Manjula R. (2016)
    Measurement techniques that provide molecular-level information are needed to elucidate the multiphase processes that produce secondary organic aerosol (SOA) species in the atmosphere. Here we demonstrate the application of ion mobility spectrometry-mass spectrometry (IMS-MS) to the simultaneous characterization of the elemental composition and molecular structures of organic species in the gas and particulate phases. Molecular ions of gas-phase organic species are measured online with IMS-MS after ionization with a custom-built nitrate chemical ionization (CI) source. This CI-IMS-MS technique is used to obtain time-resolved measurements (5 min) of highly oxidized organic molecules during the 2013 Southern Oxidant and Aerosol Study (SOAS) ambient field campaign in the forested SE US. The ambient IMS-MS signals are consistent with laboratory IMS-MS spectra obtained from single-component carboxylic acids and multicomponent mixtures of isoprene and monoterpene oxidation products. Mass-mobility correlations in the 2-D IMS-MS space provide a means of identifying ions with similar molecular structures within complex mass spectra and are used to separate and identify monoterpene oxidation products in the ambient data that are produced from different chemical pathways. Water-soluble organic carbon (WSOC) constituents of fine aerosol particles that are not resolvable with standard analytical separation methods, such as liquid chromatography (LC), are shown to be separable with IMS-MS coupled to an electrospray ionization (ESI) source. The capability to use ion mobility to differentiate between isomers is demonstrated for organosulfates derived from the reactive uptake of isomers of isoprene epoxydiols (IEPOX) onto wet acidic sulfate aerosol. Controlled fragmentation of precursor ions by collisionally induced dissociation (CID) in the transfer region between the IMS and the MS is used to validate MS peak assignments, elucidate structures of oligomers, and confirm the presence of the organosulfate functional group.
  • Xu, Z. N.; Nie, W.; Liu, Y. L.; Sun, P.; Huang, D. D.; Yan, C.; Krechmer, J.; Ye, P. L.; Xu, Z.; Qi, X. M.; Zhu, C. J.; Li, Y. Y.; Wang, T. Y.; Wang, L.; Huang, X.; Tang, R. Z.; Guo, S.; Xiu, G. L.; Fu, Q. Y.; Worsnop, D.; Chi, X. G.; Ding, A. J. (2021)
    Isoprene (2-methyl-1, 3-butadiene) is a nonmethane volatile organic compound (VOC) with the largest global emission and high reactivity. The oxidation of isoprene is crucial to atmospheric photochemistry and contributes significantly to the global formation of secondary organic aerosol. Here, we conducted comprehensive observations in polluted megacities of Nanjing and Shanghai during summer of 2018. We identified multiple functionalized isoprene oxidation products, of which 72% and 88% of the total mole concentration were nitrogen-containing species with the dominant compound being C5 dihydroxyl dinitrate (C5H10N2O8). We calculated the volatility using the group-contribution method and estimated the particle-phase concentration by equilibrium gas/particle partitioning. The results showed that the multifunctional products derived from isoprene oxidation can contribute to 2.6% of the total organic aerosol mass (0.28 +/- 0.27 mu g/m(3)), highlighting the potential importance of isoprene oxidation in polluted regions.
  • Moller, Kristian H.; Kurten, Theo; Bates, Kelvin H.; Thornton, Joel A.; Kjaergaard, Henrik G. (2019)
    Epoxide formation was established a decade ago as a possible reaction pathway for beta-hydroperoxy alkyl radicals in the atmosphere. This epoxide-forming pathway required excess energy to compete with O-2 addition, as the thermal reaction rate coefficient is many orders of magnitude too slow. However, recently, a thermal epoxide forming reaction was discovered in the ISOPOOH + OH oxidation pathway. Here, we computationally investigate the effect of substituents on the epoxide formation rate coefficient of a series of substituted beta-hydroperoxy alkyl radicals. We find that the thermal reaction is likely to be competitive with O-2 addition when the alkyl radical carbon has a OH group, which is able to form a hydrogen bond to a substituent on the other carbon atom in the epoxide ring being formed. Reactants fulfilling these requirements can be formed in the OH-initiated oxidation of many biogenic hydrocarbons. Further, we find that beta-OOR alkyl radicals react similarly to beta-OOH alkyl radicals, making epoxide formation a possible decomposition pathway in the oxidation of ROOR peroxides. GEOS-Chem modeling shows that the total annual production of isoprene dihydroxy hydroperoxy epoxide is 23 Tg, making it by far the most abundant C-5-tetrafunctional species from isoprene oxidation.