scholarly journals Chemical and isotopic composition of secondary organic aerosol generated by <i>α</i>-pinene ozonolysis

2017 ◽  
Vol 17 (10) ◽  
pp. 6373-6391 ◽  
Author(s):  
Carl Meusinger ◽  
Ulrike Dusek ◽  
Stephanie M. King ◽  
Rupert Holzinger ◽  
Thomas Rosenørn ◽  
...  
Keyword(s):  
Isotopic Composition ◽  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Bulk Composition ◽  
Isotope Analysis ◽  
Organic Aerosol ◽  
Flow Chamber ◽  
Total Carbon ◽  
Desorption Temperature ◽  
Advanced Analysis

Abstract. Secondary organic aerosol (SOA) plays a central role in air pollution and climate. However, the description of the sources and mechanisms leading to SOA is elusive despite decades of research. While stable isotope analysis is increasingly used to constrain sources of ambient aerosol, in many cases it is difficult to apply because neither the isotopic composition of aerosol precursors nor the fractionation of aerosol forming processes is well characterised. In this paper, SOA formation from ozonolysis of α-pinene – an important precursor and perhaps the best-known model system used in laboratory studies – was investigated using position-dependent and average determinations of 13C in α-pinene and advanced analysis of reaction products using thermal-desorption proton-transfer-reaction mass spectrometry (PTR-MS). The total carbon (TC) isotopic composition δ13C of the initial α-pinene was measured, and the δ13C of the specific carbon atom sites was determined using position-specific isotope analysis (PSIA). The PSIA analysis showed variations at individual positions from −6.9 to +10. 5 ‰ relative to the bulk composition. SOA was formed from α-pinene and ozone in a constant-flow chamber under dark, dry, and low-NOx conditions, with OH scavengers and in the absence of seed particles. The excess of ozone and long residence time in the flow chamber ensured that virtually all α-pinene had reacted. Product SOA was collected on two sequential quartz filters. The filters were analysed offline by heating them stepwise from 100 to 400 °C to desorb organic compounds that were (i) detected using PTR-MS for chemical analysis and to determine the O : C ratio, and (ii) converted to CO2 for 13C analysis. More than 400 ions in the mass range 39–800 Da were detected from the desorbed material and quantified using a PTR-MS. The largest amount desorbed at 150 °C. The O : C ratio of material from the front filter increased from 0.18 to 0.25 as the desorption temperature was raised from 100 to 250 °C. At temperatures above 250 °C, the O : C ratio of thermally desorbed material, presumably from oligomeric precursors, was constant. The observation of a number of components that occurred across the full range of desorption temperatures suggests that they are generated by thermal decomposition of oligomers. The isotopic composition of SOA was more or less independent of desorption temperature above 100 °C. TC analysis showed that SOA was enriched in 13C by 0.6–1.2 ‰ relative to the initial α-pinene. According to mass balance, gas-phase products will be depleted relative to the initial α-pinene. Accordingly, organic material on the back filters, which contain adsorbed gas-phase compounds, is depleted in 13C in TC by 0.7 ‰ relative to the initial α-pinene, and by 1.3 ‰ compared to SOA collected on the front filter. The observed difference in 13C between the gas and particle phases may arise from isotope-dependent changes in the branching ratios in the α-pinene + O3 reaction. Alternatively, some gas-phase products involve carbon atoms from highly enriched and depleted sites, as shown in the PSIA analysis, giving a non-kinetic origin to the observed fractionations. In either case, the present study suggests that the site-specific distribution of 13C in the source material itself governs the abundance of 13C in SOA.

scholarly journals Chemical and isotopic composition of secondary organic aerosol generated by <i>α</i>-pinene ozonolysis

2016 ◽  
Author(s):  
Carl Meusinger ◽  
Ulrike Dusek ◽  
Stephanie M. King ◽  
Rupert Holzinger ◽  
Thomas Rosenørn ◽  
...  
Keyword(s):  
Chemical Analysis ◽  
Isotopic Composition ◽  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Isotope Effects ◽  
Isotope Analysis ◽  
Carbon Isotopic Composition ◽  
Organic Aerosol ◽  
Total Carbon ◽  
Carbon Isotopic

Abstract. Secondary organic aerosol (SOA) plays a central role in air pollution and climate. However, an exact description of the sources and mechanisms leading to SOA is elusive despite decades of research. Stable isotope analysis may help to constrain atmospheric SOA budgets but the isotope effects associated with the underlying processes have to be determined in order to do so. In this paper, SOA formation from ozonolysis of α-pinene – an important precursor and perhaps the best-known model system used in laboratory studies – was investigated using stable carbon isotope analysis, position-specific isotope analysis (PSIA), and high-resolution chemical analysis based on a thermal-desorption proton-transfer-reaction mass-spectrometer (PTR-MS). SOA was formed in a constant-flow chamber under dark, dry and low-NOx conditions, with OH scavengers in the absence of seed particles. Product SOA was collected on doubly-stacked quartz filters (front and back filters). During analysis, the filters were heated stepwise over the range of 100–400 °C to desorb organic compounds that were (i) detected using PTR-MS for chemical analysis and to determine the O:C ratio, and (ii) converted to CO2 for 13C analysis. In addition, the total carbon isotopic composition of selected samples was measured. For the first time PSIA has been performed for α-pinene. More than 400 ions in the mass range from 39–800 Da were detected and quantified using the PTR-MS. The largest mass fraction desorbed from the filters at 150 °C. The measured O:C ratio of front filter material increased from 0.18 to 0.25 as the desorption temperature was raised from 100 to 250 °C. The rising trend is consistent with the fact that functionalization decreases the volatility of chemical species. At temperatures above 250 °C the O:C ratio of thermally desorbed material, presumably from oligomeric precursors, was constant. The observation of a number of components across the full range of desorption temperatures suggests that they are generated by thermal decomposition of oligomers. SOA on front filters was enriched in 13C by 0.2–2.9 ‰ relative to the initial α-pinene, at all desorption temperatures. The total carbon isotopic composition was similar to the enrichment of the major fraction desorbing at 150 °C. Gas-phase compounds desorbing from the back filters showed much lower concentrations but were depleted in 13C by 0.7 ‰ compared to the initial α-pinene and by 1.9 ‰ compared to the corresponding front filter. PSIA showed that the isotope enrichment at individual carbon positions in α-pinene ranged from −6.9 to +10.5 ‰ relative to the bulk composition. However, there was not a clear mechanistic connection between those values and the observed isotopic enrichment of bulk SOA. Instead, fragmentation reactions favouring the loss of small, isotopically light products to the gas phase are consistent with the observations. In monoterpene ozonolysis, functionalization is known to follow fragmentation, however it is the fragmentation step that seems to govern the isotope budget. The isotope effect associated with oligomerization is small. The suggested isotope effects are important for the interpretation of isotopic compositions of ambient aerosol.

scholarly journals Modeling organic aerosols in a megacity: comparison of simple and complex representations of the volatility basis set approach

2010 ◽  
Vol 10 (12) ◽  
pp. 30205-30277 ◽  
Author(s):  
M. Shrivastava ◽  
J. Fast ◽  
R. Easter ◽  
W. I. Gustafson ◽  
R. A. Zaveri ◽  
...  
Keyword(s):  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Computational Cost ◽  
Organic Aerosols ◽  
Field Measurements ◽  
Organic Aerosol ◽  
Basis Set ◽  
Aerosol Formation ◽  
Secondary Organic Aerosol Formation ◽  
The City

Abstract. The Weather Research and Forecasting model coupled with chemistry (WRF-Chem) is modified to include a volatility basis set (VBS) treatment of secondary organic aerosol formation. The VBS approach, coupled with SAPRC-99 gas-phase chemistry mechanism, is used to model gas-particle partitioning and multiple generations of gas-phase oxidation of organic vapors. In addition to the detailed 9-species VBS, a simplified mechanism using 2 volatility species (2-species VBS) is developed and tested for similarity to the 9-species VBS in terms of both mass and oxygen-to-carbon ratios of organic aerosols in the atmosphere. WRF-Chem results are evaluated against field measurements of organic aerosols collected during the MILAGRO 2006 campaign in the vicinity of Mexico City. The simplified 2-species mechanism reduces the computational cost by a factor of 2 as compared to 9-species VBS. Both ground site and aircraft measurements suggest that the 9-species and 2-species VBS predictions of total organic aerosol mass as well as individual organic aerosol components including primary, secondary, and biomass burning are comparable in magnitude. In addition, oxygen-to-carbon ratio predictions from both approaches agree within 25%, providing evidence that the 2-species VBS is well suited to represent the complex evolution of organic aerosols. Model sensitivity to amount of anthropogenic semi-volatile and intermediate volatility (S/IVOC) precursor emissions is also examined by doubling the default emissions. Both the emission cases significantly under-predict primary organic aerosols in the city center and along aircraft flight transects. Secondary organic aerosols are predicted reasonably well along flight tracks surrounding the city, but are consistently over-predicted downwind of the city. Also, oxygen-to-carbon ratio predictions are significantly improved compared to prior studies by adding 15% oxygen mass per generation of oxidation; however, all modeling cases still under-predict these ratios downwind as compared to measurements, suggesting a need to further improve chemistry parameterizations of secondary organic aerosol formation.

scholarly journals Characterization of secondary organic aerosol from heated-cooking-oil emissions: evolution in composition and volatility

2021 ◽  
Vol 21 (6) ◽  
pp. 5137-5149 ◽  
Author(s):  
Manpreet Takhar ◽  
Yunchun Li ◽  
Arthur W. H. Chan
Keyword(s):  
Gas Phase ◽  
Organic Compounds ◽  
Secondary Organic Aerosol ◽  
Carbon Number ◽  
Complex Mixture ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Atmospheric Evolution ◽  
Oxidative Aging ◽  
Cooking Oil

Abstract. Cooking emissions account for a major fraction of urban organic aerosol. It is therefore important to understand the atmospheric evolution in the physical and chemical properties of organic compounds emitted from cooking activities. In this work, we investigate the formation of secondary organic aerosol (SOA) from oxidation of gas-phase organic compounds from heated cooking oil. The chemical composition of cooking SOA is analyzed using thermal desorption–gas chromatography–mass spectrometry (TD–GC–MS). While the particle-phase composition of SOA is a highly complex mixture, we adopt a new method to achieve molecular speciation of the SOA. All the GC-elutable material is classified by the constituent functional groups, allowing us to provide a molecular description of its chemical evolution upon oxidative aging. Our results demonstrate an increase in average oxidation state (from −0.6 to −0.24) and decrease in average carbon number (from 5.2 to 4.9) with increasing photochemical aging of cooking oil, suggesting that fragmentation reactions are key processes in the oxidative aging of cooking emissions within 2 d equivalent of ambient oxidant exposure. Moreover, we estimate that aldehyde precursors from cooking emissions account for a majority of the SOA formation and oxidation products. Overall, our results provide insights into the atmospheric evolution of cooking SOA, a majority of which is derived from gas-phase oxidation of aldehydes.

scholarly journals Diurnal variations of organic molecular tracers and stable carbon isotopic compositions in atmospheric aerosols over Mt. Tai in North China Plain: an influence of biomass burning

2012 ◽  
Vol 12 (4) ◽  
pp. 9079-9124
Author(s):  
P. Q. Fu ◽  
K. Kawamura ◽  
J. Chen ◽  
J. Li ◽  
Y. L. Sun ◽  
...  
Keyword(s):  
Organic Carbon ◽  
Biomass Burning ◽  
North China Plain ◽  
North China ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Total Carbon ◽  
Stable Carbon ◽  
Isotopic Compositions ◽  
Carbon Isotopic

Abstract. Organic tracer compounds of tropospheric aerosols, as well as organic carbon (OC), elemental carbon (EC), water-soluble organic carbon (WSOC), and stable carbon isotope ratios (δ13C) of total carbon (TC) have been investigated for aerosol samples collected during early and late periods of Mount Tai eXperiment 2006 (MTX2006) field campaign in North China Plain. Total solvent extracts were investigated by gas chromatography/mass spectrometry. More than 130 organic compounds were detected in the aerosol samples. They were grouped into twelve organic compound classes, including biomass burning tracers, biogenic primary sugars, biogenic secondary organic aerosol (SOA) tracers, and anthropogenic tracers such as phthalates, hopanes and polycyclic aromatic hydrocarbons (PAHs). In early June when the field burning activities of wheat straws in North China Plain were very active, the total identified organics (2090 ± 1170 ng m−3) were double those in late June (926 ± 574 ng m−3). All the compound classes were more abundant in early June than in late June, except phthalate esters, which were higher in late June. Levoglucosan (88–1210 ng m−3, 403 ng m−3) was found as the most abundant single compound in early June, while diisobutyl phthalate was the predominant species in late June. During the biomass-burning period in early June, the diurnal trends of most of the primary and secondary organic aerosol tracers were characterized by the concentration peaks observed at mid-night or in early morning, while in late June most of the organic species peaked in late afternoon. This suggests that smoke plumes from biomass burning can uplift the aerosol particulate matter to a certain altitude and then transported to and encountered the summit of Mt. Tai during nighttime. On the basis of the tracer-based method for the estimation of biomass-burning OC, fungal-spore OC and biogenic secondary organic carbon (SOC), we estimate that an average of 24% (up to 64%) of the OC in the Mt. Tai aerosols was due to biomass burning in early June, followed by the contribution of isoprene SOC (mean 4.3%). In contrast, isoprene SOC was the main contributor (6.6%) to OC, and only 3.0% of the OC was due to biomass burning in late June. In early June, δ13C of TC (−26.6‰ to −23.2‰, mean −25.0‰) were lower than those (−23.9‰ to −21.9‰, mean −22.9‰) in late June. In addition, a strong anti-correlation was found between levoglucosan and δ13C values. This study demonstrates that crop-residue burning activities can significantly enhance the organic aerosol loading and alter the organic molecular compositions and stable carbon isotopic compositions of aerosol particles in the troposphere over North China Plain.

scholarly journals Insights into the O : C-dependent mechanisms controlling the evaporation of <i>α</i>-pinene secondary organic aerosol particles

2019 ◽  
Vol 19 (6) ◽  
pp. 4061-4073 ◽  
Author(s):  
Angela Buchholz ◽  
Andrew T. Lambe ◽  
Arttu Ylisirniö ◽  
Zijun Li ◽  
Olli-Pekka Tikkanen ◽  
...  
Keyword(s):  
Thermal Desorption ◽  
Flow Reactor ◽  
Secondary Organic Aerosol ◽  
Direct Consequence ◽  
Organic Aerosol ◽  
Oxidation Products ◽  
Desorption Temperature ◽  
Key Factor ◽  
High Volatility ◽  
Semi Solid

Abstract. The volatility of oxidation products of volatile organic compounds (VOCs) in the atmosphere is a key factor to determine if they partition into the particle phase contributing to secondary organic aerosol (SOA) mass. Thus, linking volatility and measured particle composition will provide insights into SOA formation and its fate in the atmosphere. We produced α-pinene SOA with three different oxidation levels (characterized by average oxygen-to-carbon ratio; O:C‾=0.53, 0.69, and 0.96) in an oxidation flow reactor. We investigated the particle volatility by isothermal evaporation in clean air as a function of relative humidity (RH <2 %, 40 %, and 80 %) and used a filter-based thermal desorption method to gain volatility and chemical composition information. We observed reduced particle evaporation for particles with increasing O:C‾ ratio, indicating that particles become more resilient to evaporation with oxidative aging. Particle evaporation was increased in the presence of water vapour and presumably particulate water; at the same time the resistance of the residual particles to thermal desorption was increased as well. For SOA with O:C‾=0.96, the unexpectedly large increase in mean thermal desorption temperature and changes in the thermogram shapes under wet conditions (80 % RH) were an indication of aqueous phase chemistry. For the lower O:C‾ cases, some water-induced composition changes were observed. However, the enhanced evaporation under wet conditions could be explained by the reduction in particle viscosity from the semi-solid to liquid-like range, and the observed higher desorption temperature of the residual particles is a direct consequence of the increased removal of high-volatility and the continued presence of low-volatility compounds.

Gas-phase kinetics modifies the CCN activity of a biogenic SOA

2018 ◽  
Vol 20 (9) ◽  
pp. 6591-6597
Author(s):  
A. E. Vizenor ◽  
A. A. Asa-Awuku
Keyword(s):  
Particle Size ◽  
Thermodynamic Properties ◽  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Cloud Condensation Nuclei ◽  
Organic Aerosol ◽  
Aerosol Composition ◽  
Phase Partitioning ◽  
Gas Phase Kinetics ◽  
Ccn Activity

Cloud condensation nuclei (CCN) activity and the hygroscopicity of secondary organic aerosol (SOA) depends on the particle size and composition, explicitly, the thermodynamic properties of the aerosol solute and subsequent interactions with water. The gas-to-aerosol phase partitioning is critical for aerosol composition and thus gas-phase vapors and kinetics can play an important role in the CCN activity of SOA.

scholarly journals Development of aroCACM/MPMPO 1.0: a model to simulate secondary organic aerosol from aromatic precursors in regional models

2016 ◽  
Vol 9 (6) ◽  
pp. 2143-2151 ◽  
Author(s):  
Matthew L. Dawson ◽  
Jialu Xu ◽  
Robert J. Griffin ◽  
Donald Dabdub
Keyword(s):  
Gas Phase ◽  
Atmospheric Chemistry ◽  
Urban Areas ◽  
Secondary Organic Aerosol ◽  
Three Dimensional ◽  
Organic Aerosol ◽  
Phase Partitioning ◽  
California Institute Of Technology ◽  
Institute Of Technology ◽  
Three Dimensional Models

Abstract. The atmospheric oxidation of aromatic compounds is an important source of secondary organic aerosol (SOA) in urban areas. The oxidation of aromatics depends strongly on the levels of nitrogen oxides (NOx). However, details of the mechanisms by which oxidation occurs have only recently been elucidated. Xu et al. (2015) developed an updated version of the gas-phase Caltech Atmospheric Chemistry Mechanism (CACM) designed to simulate toluene and m-xylene oxidation in chamber experiments over a range of NOx conditions. The output from such a mechanism can be used in thermodynamic predictions of gas–particle partitioning leading to SOA. The current work reports the development of a model for SOA formation that combines the gas-phase mechanism of Xu et al. (2015) with an updated lumped SOA-partitioning scheme (Model to Predict the Multi-phase Partitioning of Organics, MPMPO) that allows partitioning to multiple aerosol phases and that is designed for use in larger-scale three-dimensional models. The resulting model is termed aroCACM/MPMPO 1.0. The model is integrated into the University of California, Irvine – California Institute of Technology (UCI-CIT) Airshed Model, which simulates the South Coast Air Basin (SoCAB) of California. Simulations using 2012 emissions indicate that “low-NOx” pathways to SOA formation from aromatic oxidation play an important role, even in regions that typically exhibit high-NOx concentrations.

scholarly journals Aqueous chemistry and its role in secondary organic aerosol (SOA) formation

2010 ◽  
Vol 10 (21) ◽  
pp. 10521-10539 ◽  
Author(s):  
Y. B. Lim ◽  
Y. Tan ◽  
M. J. Perri ◽  
S. P. Seitzinger ◽  
B. J. Turpin
Keyword(s):  
Organic Acids ◽  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Water Soluble ◽  
Base Catalysis ◽  
Radical Reactions ◽  
Oh Radicals ◽  
Aqueous Chemistry ◽  
Radical Chemistry

Abstract. There is a growing understanding that secondary organic aerosol (SOA) can form through reactions in atmospheric waters (i.e., clouds, fogs, and aerosol water). In clouds and wet aerosols, water-soluble organic products of gas-phase photochemistry dissolve into the aqueous phase where they can react further (e.g., with OH radicals) to form low volatility products that are largely retained in the particle phase. Organic acids, oligomers and other products form via radical and non-radical reactions, including hemiacetal formation during droplet evaporation, acid/base catalysis, and reaction of organics with other constituents (e.g., NH4+). This paper provides an overview of SOA formation through aqueous chemistry, including atmospheric evidence for this process and a review of radical and non-radical chemistry, using glyoxal as a model precursor. Previously unreported analyses and new kinetic modeling are reported herein to support the discussion of radical chemistry. Results suggest that reactions with OH radicals tend to be faster and form more SOA than non-radical reactions. In clouds these reactions yield organic acids, whereas in wet aerosols they yield large multifunctional humic-like substances formed via radical-radical reactions and their O/C ratios are near 1.

scholarly journals The formation of secondary organic aerosol from the isoprene + OH reaction in the absence of NO<sub>x</sub>

2009 ◽  
Vol 9 (17) ◽  
pp. 6541-6558 ◽  
Author(s):  
T. E. Kleindienst ◽  
M. Lewandowski ◽  
J. H. Offenberg ◽  
M. Jaoui ◽  
E. O. Edney
Keyword(s):  
Gas Phase ◽  
Secondary Organic Aerosol ◽  
Organic Aerosol ◽  
Organic Peroxide ◽  
Enthalpy Of Vaporization ◽  
Steady State Mode ◽  
Reaction Conditions ◽  
Independent Technique ◽  
Aerosol Parameters ◽  
Physical And Chemical

Abstract. The reaction of isoprene (C5H8) with hydroxyl radicals has been studied in the absence of nitrogen oxides (NOx) to determine physical and chemical characteristics of the secondary organic aerosol formed. Experiments were conducted using a smog chamber operated in a steady-state mode permitting measurements of moderately low aerosol levels. GC-MS analysis was conducted to measure methyl butenediols in the gas phase and polyols in the aerosol phase. Analyses were made to obtain several bulk aerosol parameters from the reaction including values for the organic mass to organic carbon ratio, the effective enthalpy of vaporization (ΔHvapeff), organic peroxide fraction, and the aerosol yield. The gas phase analysis showed the presence of methacrolein, methyl vinyl ketone, and four isomers of the methyl butenediols. These gas-phase compounds may serve as precursors for one or more of several compounds detected in the aerosol phase including 2-methylglyceric acid, three 2-methyl alkenetriols, and two 2-methyl tetrols. In contrast to most previous studies, the 2-methyl tetrols (and the 2-methyl alkenetriols) were found to form in the absence of acidic sulfate aerosol. However, reaction conditions did not favor the production of HO2 radicals, thus allowing RO2+RO2 reactions to proceed more readily than if higher HO2 levels had been generated. SOA/SOC (i.e. OM/OC) was found to average 1.9 in the absence of NOx. The effective enthalpy of vaporization was measured as 38.6 kJ mol−1, consistent with values used previously in modeling studies. The yields in this work (using an independent technique than used previously) are lower than those of Kroll et al. (2006) for similar aerosol masses. SOC yields reported in this work range from 0.5–1.4% for carbon masses between 17 and 49 μgC m−3.

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