Browsing by Subject "ISOPRENE"

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  • Kurten, Theo; Moller, Kristian H.; Nguyen, Tran B.; Schwantes, Rebecca H.; Misztal, Pawel K.; Su, Luping; Wennberg, Paul O.; Fry, Juliane L.; Kjaergaard, Henrik G. (2017)
    Oxidation of monoterpenes (C10H16) by nitrate radicals (NO3) constitutes an important source of atmospheric secondary organic aerosol (SOA) and organonitrates. However, knowledge of the mechanisms of their formation is incomplete and differences in yields between similar monoterpenes are poorly understood. In particular, yields of SOA and organonitrates from alpha-pinene + NO3 are low, while those from Delta(3)-carene + NO3 are high. Using computational methods, we suggest that bond scission of the nitrooxy alkoxy radicals from Delta(3)-carene lead to the formation of reactive keto-nitrooxy-alkyl radicals, which retain the nitrooxy moiety and can undergo further reactions to form SOA. By contrast, bond scissions of the nitrooxy alkoxy radicals from alpha-pinene lead almost exclusively to the formation of the relatively unreactive and volatile product pinonaldehyde (C10H16O2), thereby limiting organonitrate and SOA formation. This hypothesis is supported by laboratory experiments that quantify products of the reaction of alpha-pinene + NO3 under atmospherically relevant conditions.
  • 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.
  • Eskola, Arkke J.; Döntgen, Malte; Rotavera, Brandon; Caravan, Rebecca L.; Welz, Oliver; Savee, John D.; Osborn, David L.; Shallcross, Dudley E.; Percival, Carl J.; Taatjes, Craig A. (2018)
    Methyl vinyl ketone (MVK) and methacrolein (MACR) are important intermediate products in atmospheric degradation of volatile organic compounds, especially of isoprene. This work investigates the reactions of the smallest Criegee intermediate, CH2OO, with its co-products from isoprene ozonolysis, MVK and MACR, using multiplexed photoionization mass spectrometry (MPIMS), with either tunable synchrotron radiation from the Advanced Light Source or Lyman-alpha (10.2 eV) radiation for photoionization. CH2OO was produced via pulsed laser photolysis of CH(2)l(2) in the presence of excess O-2. Time-resolved measurements of reactant disappearance and of product formation were performed to monitor reaction progress; first order rate coefficients were obtained from exponential fits to the CH2OO decays. The bimolecular reaction rate coefficients at 300 K and 4 Torr are k(CH2OO + MVK) = (5.0 +/- 0.4) x 10(-13) cm(3) s(-1) and k(CH2OO + MACR) = (4.4 +/- 1.0) x 10(-13) cm(3) s(-1), where the stated +/- 2 sigma uncertainties are statistical uncertainties. Adduct formation is observed for both reactions and is attributed to the formation of a secondary ozonides (1,2,4-trioxolanes), supported by master equation calculations of the kinetics and the agreement between measured and calculated adiabatic ionization energies. Kinetics measurements were also performed for a possible bimolecular CH2OO + CO reaction and for the reaction of CH2OO with CF3CHCH2 at 300 K and 4 Torr. For CH2OO + CO, no reaction is observed and an upper limit is determined: k(CH2OO + CO) <2 x 10(-16) cm(3) s(-1). For CH2OO + CF3CHCH2, an upper limit of k(CH2OO + CF3CHCH2) <2 x 10(-14) cm(3) s(-1) is obtained.
  • Lee, Ben H.; Mohr, Claudia; Lopez-Hilfiker, Felipe D.; Lutz, Anna; Hallquist, Mattias; Lee, Lance; Romer, Paul; Cohen, Ronald C.; Iyer, Siddharth; Kurten, Theo; Hu, Weiwei; Day, Douglas A.; Campuzano-Jost, Pedro; Jimenez, Jose L.; Xu, Lu; Ng, Nga Lee; Guo, Hongyu; Weber, Rodney J.; Wild, Robert J.; Brown, Steven S.; Koss, Abigail; de Gouw, Joost; Olson, Kevin; Goldstein, Allen H.; Seco, Roger; Kim, Saewung; McAvey, Kevin; Shepson, Paul B.; Starn, Tim; Baumann, Karsten; Edgerton, Eric S.; Liu, Jiumeng; Shilling, John E.; Miller, David O.; Brune, William; Schobesberger, Siegfried; D'Ambro, Emma L.; Thornton, Joel A. (2016)
    Speciated particle-phase organic nitrates (pONs) were quantified using online chemical ionization MS during June and July of 2013 in rural Alabama as part of the Southern Oxidant and Aerosol Study. A large fraction of pONs is highly functionalized, possessing between six and eight oxygen atoms within each carbon number group, and is not the common first generation alkyl nitrates previously reported. Using calibrations for isoprene hydroxynitrates and the measured molecular compositions, we estimate that pONs account for 3% and 8% of total submicrometer organic aerosol mass, on average, during the day and night, respectively. Each of the isoprene-and monoterpenes-derived groups exhibited a strong diel trend consistent with the emission patterns of likely biogenic hydrocarbon precursors. An observationally constrained diel box model can replicate the observed pON assuming that pONs (i) are produced in the gas phase and rapidly establish gas-particle equilibrium and (ii) have a short particle-phase lifetime (similar to 2-4 h). Such dynamic behavior has significant implications for the production and phase partitioning of pONs, organic aerosol mass, and reactive nitrogen speciation in a forested environment.
  • Jaars, Kerneels; van Zyl, Pieter G.; Beukes, Johan P.; Hellen, Heidi; Vakkari, Ville; Josipovic, Micky; Venter, Andrew D.; Räsänen, Matti; Knoetze, Leandra; Cilliers, Dirk P.; Siebert, Stefan J.; Kulmala, Markku; Rinne, Janne; Guenther, Alex; Laakso, Lauri; Hakola, Hannele (2016)
    Biogenic volatile organic compounds (BVOCs) play an important role in the chemistry of the troposphere, especially in the formation of tropospheric ozone (O-3) and secondary organic aerosols (SOA). Ecosystems produce and emit a large number of BVOCs. It is estimated on a global scale that approximately 90% of annual BVOC emissions are from terrestrial sources. In this study, measurements of BVOCs were conducted at the Welgegund measurement station (South Africa), which is considered to be a regionally representative background site situated in savannah grasslands. Very few BVOC measurements exist for savannah grasslands and results presented in this study are the most extensive for this type of landscape. Samples were collected twice a week for 2 h during the daytime and 2 h during the night-time through two long-term sampling campaigns from February 2011 to February 2012 and from December 2013 to February 2015, respectively. Individual BVOCs were identified and quantified using a thermal desorption instrument, which was connected to a gas chromatograph and a mass selective detector. The annual median concentrations of isoprene, 2-methyl-3-butene-2-ol (MBO), monoterpene and sesquiterpene (SQT) during the first campaign were 14, 7, 120 and 8 pptv, respectively, and 14, 4, 83 and 4 pptv, respectively, during the second campaign. The sum of the concentrations of the monoterpenes were at least an order of magnitude higher than the concentrations of other BVOC species during both sampling campaigns, with alpha-pinene being the most abundant species. The highest BVOC concentrations were observed during the wet season and elevated soil moisture was associated with increased BVOC concentrations. However, comparisons with measurements conducted at other landscapes in southern Africa and the rest of the world that have more woody vegetation indicated that BVOC concentrations were, in general, significantly lower for savannah grasslands. Furthermore, BVOC concentrations were an order of magnitude lower compared to total aromatic concentrations measured at Welgegund. An analysis of concentrations by wind direction indicated that isoprene concentrations were higher from the western sector that is considered to be a relatively clean regional background region with no large anthropogenic point sources, while wind direction did not indicate any significant differences in the concentrations of the other BVOC species. Statistical analysis indicated that soil moisture had the most significant impact on atmospheric levels of MBO, monoterpene and SQT concentrations, whereas temperature had the greatest influence on isoprene levels. The combined O-3 formation potentials of all the BVOCs measured calculated with maximum incremental reactivity (MIR) coefficients during the first and second campaign were 1162 and 1022 pptv, respectively. alpha-Pinene and limonene had the highest reaction rates with O3, whereas isoprene exhibited relatively small contributions to O3 depletion. Limonene, alpha-pinene and terpinolene had the largest contributions to the OH reactivity of BVOCs measured at Welgegund for all of the months during both sampling campaigns.
  • Hakola, H; Tarvainen, V; Bäck, Jaana; Ranta, H; Bonn, Boris; Rinne, Janne; Kulmala, Markku (2006)
  • McFiggans, Gordon; Mentel, Thomas F.; Wildt, Juergen; Pullinen, Iida; Kang, Sungah; Kleist, Einhard; Schmitt, Sebastian; Springer, Monika; Tillmann, Ralf; Wu, Cheng; Zhao, Defeng; Hallquist, Mattias; Faxon, Cameron; Le Breton, Michael; Hallquist, Asa M.; Simpson, David; Bergstroem, Robert; Jenkin, Michael E.; Ehn, Mikael; Thornton, Joel A.; Alfarra, M. Rami; Bannan, Thomas J.; Percival, Carl J.; Priestley, Michael; Topping, David; Kiendler-Scharr, Astrid (2019)
    Secondary organic aerosol contributes to the atmospheric particle burden with implications for air quality and climate. Biogenic volatile organic compounds such as terpenoids emitted from plants are important secondary organic aerosol precursors with isoprene dominating the emissions of biogenic volatile organic compounds globally. However, the particle mass from isoprene oxidation is generally modest compared to that of other terpenoids. Here we show that isoprene, carbon monoxide and methane can each suppress the instantaneous mass and the overall mass yield derived from monoterpenes in mixtures of atmospheric vapours. We find that isoprene 'scavenges' hydroxyl radicals, preventing their reaction with monoterpenes, and the resulting isoprene peroxy radicals scavenge highly oxygenated monoterpene products. These effects reduce the yield of low-volatility products that would otherwise form secondary organic aerosol. Global model calculations indicate that oxidant and product scavenging can operate effectively in the real atmosphere. Thus highly reactive compounds (such as isoprene) that produce a modest amount of aerosol are not necessarily net producers of secondary organic particle mass and their oxidation in mixtures of atmospheric vapours can suppress both particle number and mass of secondary organic aerosol. We suggest that formation mechanisms of secondary organic aerosol in the atmosphere need to be considered more realistically, accounting for mechanistic interactions between the products of oxidizing precursor molecules (as is recognized to be necessary when modelling ozone production).
  • Lee, Ben H.; Lopez-Hilfiker, Felipe D.; D'Ambro, Emma L.; Zhou, Putian; Boy, Michael; Petäjä, Tuukka; Hao, Liqing; Virtanen, Annele; Thornton, Joel A. (2018)
    We present hourly online observations of molecular compositions (CxHyOzN0-1) and abundances of oxygenated organic species in gas and submicron particle phases from April to June of 2014 as part of the Biogenic Aerosols-Effects on Cloud and Climate (BAECC) campaign. Measurements were made using the Filter Inlet for Gases and AEROsols coupled to a high-resolution time-of-flight iodide-adduct ionization mass spectrometer (FIGAERO-CIMS) located atop a 35m tall tower, about 10m above a boreal forest canopy at the SMEAR II research station in Hyytiala, Finland. Semi-volatile and highly oxygenated multifunctional (HOM) organic species possessing from 1 up to 20 carbon atoms, and with as few as 2 and as many as 16 oxygen atoms, were routinely observed. Utilizing non-negative matrix factorization, we determined that > 90 and > 99% of the organic mass in the gas and particle phases, respectively, exhibited one of three distinct diel trends: one in which abundances were enhanced at daytime, another in the early morning hours, and thirdly during nighttime. Particulate organic nitrates contributed similar to 35% to the total organic aerosol mass loading at night during BAECC, much higher than observed by the same instrument package at a mixed-deciduous forest site in the southeastern US that experienced higher nighttime concentrations of nitrogen oxides. Unique HOM monomers (defined here as those with 10 carbon and 7 or more oxygen atoms) and dimers (at least 16 carbon atoms), with and without a nitrogen atom, were found in most of the three subgroups of both phases. We show the potential to connect these groupings of compounds based on their distinct behavior in time to the expected chemical conditions (biogenic VOC precursor, oxidant type, etc.) responsible for their production. A suite of nitrated dimer-like compounds was detected in both the gas and particle phases, suggesting a potential role for the formation of low-volatility organics from NO3-radical-driven, as well as daytime NO-influenced, monoterpene chemistry.
  • Mielonen, Tero; Hienola, Anca; Kuhn, Thomas; Merikanto, Joonas; Lipponen, Antti; Bergman, Tommi; Korhonen, Hannele; Kolmonen, Pekka; Sogacheva, Larisa; Ghent, Darren; Pitkanen, Mikko R. A.; Arola, Antti; de Leeuw, Gerrit; Kokkola, Harri (2018)
    Satellite data suggest that summertime aerosol optical depth (AOD) over the southeastern USA depends on the air/land surface temperature, but the magnitude of the radiative effects caused by this dependence remains unclear. To quantify these radiative effects, we utilized several remote sensing datasets and ECMWF reanalysis data for the years 2005-2011. In addition, the global aerosol-climate model ECHAM-HAMMOZ was used to identify the possible processes affecting aerosol loads and their dependence on temperature over the studied region. The satellite-based observations suggest that changes in the total summertime AOD in the southeastern USA are mainly governed by changes in anthropogenic emissions. In addition, summertime AOD exhibits a dependence on southerly wind speed and land surface temperature (LST). Transport of sea salt and Saharan dust is the likely reason for the wind speed dependence, whereas the temperature-dependent component is linked to temperature-induced changes in the emissions of biogenic volatile organic compounds (BVOCs) over forested regions. The remote sensing datasets indicate that the biogenic contribution increases AOD with increasing temperature by approximately (7 +/- 6) x 10(-3) K-1 over the southeastern USA. In the model simulations, the increase in summertime AOD due to temperature-enhanced BVOC emissions is of a similar magnitude, i.e., (4 +/- 1) x 10(-3) K-1. The largest source of BVOC emissions in this region is broadleaf trees, thus if the observed temperature dependence of AOD is caused by biogenic emissions the dependence should be the largest in the vicinity of forests. Consequently, the analysis of the remote sensing data shows that over mixed forests the biogenic contribution increases AOD by approximately (27 +/- 13) x 10(-3) K-1, which is over four times higher than the value for over the whole domain, while over other land cover types in the study region (woody savannas and cropland/natural mosaic) there is no clear temperature dependence. The corresponding clear-sky direct radiative effect (DRE) of the observation-based biogenic AOD is -0.33 +/- 0.29 W/m(2)/K for the whole domain and -1.3 +/- 0.7 W/m(2)/K over mixed forests only. The model estimate of the regional clear-sky DRE for biogenic aerosols is similar to the observational estimate for the whole domain: -0.29 +/- 0.09 W/m(2)/K. Furthermore, the model simulations showed that biogenic emissions have a significant effective radiative forcing (ERF) in this region: -1.0 +/- 0.5 W/m(2)/K.
  • Hellen, Heidi; Schallhart, Simon; Praplan, Arnaud P.; Petäjä, Tuukka; Hakola, Hannele (2017)
    An in situ method for studying gas-phase C-2-C-7 monocarboxylic volatile organic acids (VOAs) in ambient air was developed and evaluated. Samples were collected directly into the cold trap of the thermal desorption unit (TD) and analysed in situ using a gas chromatograph (GC) coupled to a mass spectrometer (MS). A polyethylene glycol column was used for separating the acids. The method was validated in the laboratory and tested on the ambient air of a boreal forest in June 2015. Recoveries of VOAs from fluorinated ethylene propylene (FEP) and heated stainless steel inlets ranged from 83 to 123 %. Different VOAs were fully desorbed from the cold trap and well separated in the chromatograms. Detection limits varied between 1 and 130 pptv and total uncertainty of the method at mean ambient mixing ratios was between 16 and 76 %. All straight chain VOAs except heptanoic acid in the ambient air measurements were found with mixing ratios above the detection limits. The highest mixing ratios were found for acetic acid and the highest relative variations for hexanoic acid. In addition, mixing ratios of acetic and propanoic acids measured by the novel GC-MS method were compared with proton-mass-transfer time-off-light mass spectrometer (PTR-TOFMS) data. Both instruments showed similar variations, but differences in the mixing ratio levels were significant.