Browsing by Subject "atmospheric chemistry"

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  • Berndt, Torsten; Scholz, Wiebke; Mentler, Bernhard; Fischer, Lukas; Herrmann, Hartmut; Kulmala, Markku; Hansel, Armin (2018)
    Hydrocarbons are emitted into the Earth's atmosphere in very large quantities by human and biogenic activities. Their atmospheric oxidation processes almost exclusively yield RO2 radicals as reactive intermediates whose atmospheric fate is not yet fully unraveled. Herein, we show that gas-phase reactions of two RO2 radicals produce accretion products composed of the carbon backbone of both reactants. The rates for accretion product formation are very high for RO2 radicals bearing functional groups, competing with those of the corresponding reactions with NO and HO2. This pathway, which has not yet been considered in the modelling of atmospheric processes, can be important, or even dominant, for the fate of RO2 radicals in all areas of the atmosphere. Moreover, the vapor pressure of the formed accretion products can be remarkably low, characterizing them as an effective source for the secondary organic aerosol.
  • Lawler, Michael J.; Rissanen, Matti P.; Ehn, Mikael; Mauldin, R. Lee; Sarnela, Nina; Sipilä, Mikko; Smith, James N. (2018)
    New particle formation (NPF) is an important contributor to particle number in many locations, but the chemical drivers for this process are not well understood. Daytime NPF events occur regularly in the springtime Finnish boreal forest and strongly impact aerosol abundance. In April 2014 size-resolved chemical measurements of ambient nanoparticles were made using the Time-of-Flight Thermal Desorption Chemical ionization Mass Spectrometer and we report results from two NPF events. While growth overall was dominated by terpene oxidation products, newly formed 20-70nm particles showed enhancement in apparent alkanoic acids. The events occurred on days with rapid transport of marine air, which correlated with low background aerosol loading and higher gas phase methanesulfonic acid levels. These results are broadly consistent with previous studies on Nordic NPF but indicate that further attention should be given to the sources and role of non-terpenoid organics and the possible contribution of transported marine compounds in this process. Plain Language Summary Clouds are an enormously important part of the climate system because they control the radiation entering and leaving the Earth. Clouds form as water condenses onto small particles called cloud condensation nuclei. These particles can be directly emitted from the Earth's surface, like sea spray, for example, or they can form in the atmosphere out of precursor gases. We have measured the composition of these atmosphere-formed particles to understand better how this process works in the Nordic boreal forest. We found that a diverse mix of processes and molecules are likely involved, possibly including the transport of materials from the ocean. While these results will ultimately lead to a better understanding of ocean-land-cloud interactions, they currently indicate that more work is needed to learn the processes involved.
  • Lee, Ben H.; Lopez-Hilfiker, Felipe D.; Veres, Patrick R.; McDuffie, Erin E.; Fibiger, Dorothy L.; Sparks, Tamara L.; Ebben, Carlena J.; Green, Jaime R.; Schroder, Jason C.; Campuzano-Jost, Pedro; Iyer, Siddharth; D'Ambro, Emma L.; Schobesberger, Siegfried; Brown, Steven S.; Wooldridge, Paul J.; Cohen, Ronald C.; Fiddler, Marc N.; Bililign, Solomon; Jimenez, Jose L.; Kurten, Theo; Weinheimer, Andrew J.; Jaegle, Lyatt; Thornton, Joel A. (2018)
    We describe the University of Washington airborne high-resolution time-of-flight chemical ionization mass spectrometer (HRToF-CIMS) and evaluate its performance aboard the NCAR-NSF C-130 aircraft during the recent Wintertime INvestigation of Transport, Emissions and Reactivity (WINTER) experiment in February-March of 2015. New features include (i) a computer-controlled dynamic pinhole that maintains constant mass flow-rate into the instrument independent of altitude changes to minimize variations in instrument response times; (ii) continuous addition of low flow-rate humidified ultrahigh purity nitrogen to minimize the difference in water vapor pressure, hence instrument sensitivity, between ambient and background determinations; (iii) deployment of a calibration source continuously generating isotopically labeled dinitrogen pentoxide ((N2O5)-N-15) for in-flight delivery; and (iv) frequent instrument background determinations to account for memory effects resulting from the interaction between sticky compounds and instrument surface following encounters with concentrated air parcels. The resulting improvements to precision and accuracy, along with the simultaneous acquisition of these species and the full set of their isotopologues, allow for more reliable identification, source attribution, and budget accounting, for example, by speciating the individual constituents of nocturnal reactive nitrogen oxides (NOz=ClNO2+2xN(2)O(5)+HNO3+etc.). We report on an expanded set of species quantified using iodide-adduct ionization such as sulfur dioxide (SO2), hydrogen chloride (HCl), and other inorganic reactive halogen species including hypochlorous acid, nitryl chloride, chlorine, nitryl bromide, bromine, and bromine chloride (HOCl, ClNO2, Cl-2, BrNO2, Br-2, and BrCl, respectively).
  • Kuerten, Andreas; Jokinen, Tuija; Simon, Mario; Sipilä, Mikko; Sarnela, Nina; Junninen, Heikki; Adamov, Alexey; Almeida, Joao; Amorim, Antonio; Bianchi, Federico; Breitenlechner, Martin; Dommen, Josef; Donahue, Neil M.; Duplissy, Jonathan; Ehrhart, Sebastian; Flagan, Richard C.; Franchin, Alessandro; Hakala, Jani; Hansel, Armin; Heinritzi, Martin; Hutterli, Manuel; Kangasluoma, Juha; Kirkby, Jasper; Laaksonen, Ari; Lehtipalo, Katrianne; Leiminger, Markus; Makhmutov, Vladimir; Mathot, Serge; Onnela, Antti; Petäjä, Tuukka; Praplan, Arnaud P.; Riccobono, Francesco; Rissanen, Matti P.; Rondo, Linda; Schobesberger, Siegfried; Seinfeld, John H.; Steiner, Gerhard; Tome, Antonio; Troestl, Jasmin; Winkler, Paul M.; Williamson, Christina; Wimmer, Daniela; Ye, Penglin; Baltensperger, Urs; Carslaw, Kenneth S.; Kulmala, Markku; Worsnop, Douglas R.; Curtius, Joachim (2014)
  • Li, Haiyan; Väliranta, Minna; Mäki, Mari; Kohl, Lukas; Sannel, Britta; Pumpanen, Jukka; Koskinen, Markku; Bäck, Jaana; Bianchi, Federico (2020)
    Volatile organic compounds (VOCs) play an essential role in climate change and air pollution by modulating tropospheric oxidation capacity and providing precursors for ozone and aerosol formation. Arctic permafrost buries large quantities of frozen soil carbon, which could be released as VOCs with permafrost thawing or collapsing as a consequence of global warming. However, due to the lack of reported studies in this field and the limited capability of the conventional measurement techniques, it is poorly understood how much VOCs could be emitted from thawing permafrost and the chemical speciation of the released VOCs. Here we apply a Vocus proton-transfer-reaction time-of-flight mass spectrometer (PTR-TOF) in laboratory incubations for the first time to examine the release of VOCs from thawing permafrost peatland soils sampled from Finnish Lapland. The warming-induced rapid VOC emissions from the thawing soils were mainly attributed to the direct release of old, trapped gases from the permafrost. The average VOC fluxes from thawing permafrost were four times as high as those from the active layer (the top layer of soil in permafrost terrain). The emissions of less volatile compounds, i.e. sesquiterpenes and diterpenes, increased substantially with rising temperatures. Results in this study demonstrate the potential for substantive VOC releases from thawing permafrost. We anticipate that future global warming could stimulate VOC emissions from the Arctic permafrost, which may significantly influence the Arctic atmospheric chemistry and climate change.
  • Elm, Jonas; Myllys, Nanna; Kurten, Theo (2017)
    We investigate the molecular interactions between phosphoric acid and common atmospheric nucleation precursors using computational methods. The equilibrium geometries and vibrational frequencies are obtained using the three DFT functionals M06-2X, PW91 and B97X-D. The single-point energy is corrected using a high-level CCSD(T)-F12a/VDZ-F12 calculation. The molecular interaction between phosphoric acid and sulphuric acid is found to be strong with reaction free energy of similar magnitude as the interaction between dimethylamine and sulphuric acid. The strong hydrogen bonding of phosphoric acid to sulphuric acid indicates that concentrations of as low as 10(2)-10(4) molecules/cm(3) will offer equivalent or higher stability as the sulphuric acid dimer for the formation of atmospheric molecular clusters. We assess and utilise the DLPNO-CCSD(T) method for studying larger clusters involving phosphoric acid and sulphuric acid and find that having a phosphoric acid molecule present in the cluster enhances the further addition of sulphuric acid molecules. [GRAPHICS] .
  • Vuorio, Niko (Helsingin yliopisto, 2021)
    The Criegee intermediates (CIs) have been the topic for several studies and their role in global atmospheric chemistry is becoming better understood. Isoprene and monoterpenes form a large portion of the total biogenic volatile organic compound emissions in the forested regions of the world, isoprene being the most abundant non-methane hydrocarbon in the Earth's atmosphere. The carbon-carbon double bonds in these compounds are efficiently ozonized (the reaction where an unsaturated compound reacts with ozone) in the atmosphere leading to primary ozonides that subsequently decompose into Criegee intermediates and carbonyl compound molecules. Approximately 50 % of the CIs derived from acyclic alkenes immediately decompose in unimolecular reactions forming, e.g., hydroxyl radicals, the most important oxidizing species in the Earth’s atmosphere. The remainder is stabilized in atmospheric conditions in collisions with other molecules and are subsequently called stabilized Criegee intermediates (sCI). The sCI yields are often smaller, around 20 %, for Criegee intermediates formed in ozonolysis of cyclic alkenes, such as α-pinene. These sCIs can further react with atmospheric constituents (H2O, (H2O)2, SO2, NO2, organic acids etc.) in bimolecular reactions or decompose/isomerize in unimolecular reactions. The bimolecular reactions of sCIs with SO2 contribute significantly to the formation of atmospheric gas phase sulphuric acid and as such are an important factor in nucleation and formation of clouds. In the lower atmosphere, H2SO4 also has adverse health effects on humans and animals and causes corrosion of building materials. Additionally, unimolecular decay and bimolecular reactions of sCIs produce OH radicals. The experimental studies done so far have largely focused on the few simplest sCIs, i.e., formaldehyde oxide (H2COO), acetaldehyde oxide (CH3COO), and acetone oxide ((CH3)2COO). The studies on more complex sCIs, such as methyl vinyl ketone oxide and sCIs formed via ozonolysis of terpenes, are mostly done computationally. The literature review part of this work presents the basic mechanisms of formation and natural removal of sCIs as well as results of recent direct kinetic studies of sCIs with focus on the simplest ones (CH2OO, CH3CHOO, and (CH3)2COO). The methods of detection used in experimental studies are also considered. The experimental section concentrates on measurements of unimolecular decay kinetics of acetone oxide (CH3)2COO above and below room temperature using a new photolytic precursor (CH3)2CIBr. In the experimental section also the apparatus utilized in the research is presented along with the modifications and improvements made on the setup in this work. The calibrations done to ensure accurate measurements are also presented.