The oleic acid-ozone heterogeneous reaction system: products, kinetics, secondary chemistry, and atmospheric implications of a model system ? a review

International audienceThe heterogeneous processing of organic aerosols by trace oxidants has many implications to atmospheric chemistry and climate regulation. This review covers a model heterogeneous reaction system (HRS): the oleic acid-ozone HRS and other reaction systems featuring fatty acids, and their derivatives. The analysis of the commonly observed aldehyde and organic acid products of ozonolysis (azelaic acid, nonanoic acid, 9-oxononanoic acid, nonanal) is described. The relative product yields are noted and explained by the observation of secondary chemical reactions. The secondary reaction products arising from reactive Criegee intermediates are mainly peroxidic, notably secondary ozonides and ?-acyloxyalkyl hydroperoxide oligomers and polymers, and their formation is in accord with solution and liquid-phase ozonolysis. These highly oxygenated products are of low volatility and hydrophilic which may enhance the ability of particles to act as cloud condensation nuclei (CCN). The kinetic description of this HRS is critically reviewed. Most kinetic studies suggest this oxidative processing is either a near surface reaction that is limited by the diffusion of ozone or a surface based reaction. Internally mixed particles and coatings represent the next stage in the progression towards more realistic proxies of tropospheric organic aerosols and a description of the products and the kinetics resulting from the ozonolysis of these proxies, which are based on fatty acids or their derivatives, is presented. Finally, the main atmospheric implications of oxidative processing of particulate containing fatty acids are presented. These implications include the extended lifetime of unsaturated species in the troposphere facilitated by the presence of solids, semi-solids or viscous phases, and an enhanced rate of ozone uptake by particulate unsaturates compared to corresponding gas-phase organics. Ozonolysis of oleic acid enhances its CCN activity, which implies that oxidatively processed particulate may contribute to indirect forcing of radiation

Photoelectron Resonance Capture Ionization Aerosol Mass Spectrometry of Organic Particulate Matter

Organic aerosols are ubiquitous to the lower atmosphere and there is growing concern about their impact on climate and human health. These aerosols typically have multicomponent compositions that change over time in part due to oxidation by reactive trace gases, such as ozone. A current challenge to the atmospheric research community is to develop better methods of analysis of these particles. Photoelectron resonance capture ionization aerosol mass spectrometry (PERCI-AMS) is an online mass spectrometric method that has been applied to the analysis of organic aerosols. One of its key advantages is that it employs low energy (~ 0 eV) photoelectrons in the ion forming process, which has been shown to minimize fragmentation in the organic analytes, thus simplifying mass spectral interpretation. This dissertation focuses on the application of PERCI-AMS to the analysis of organic particles. Initial emphasis is placed on the heterogeneous reaction of gas phase ozone with liquid oleic acid particles. Products identified included carboxylic acids, aldehydes, and peroxides including alpha-acyloxyalkyl hydroperoxides polymers. The evidence of peroxidic products suggested the stabilization of carbonyl oxide intermediates (i.e. Criegee intermediates) that are formed during ozonolysis. Subsequent PERCI-AMS experiments investigated the reactivity of the stabilized Criegee intermediates. This included investigating the reaction of Criegee intermediates with unsaturated fatty acids and methyl esters. A novel ketone-forming reaction is described in these systems, suggesting the Criegee intermediates can react at a carbon-carbon double bond. Further PERCI-AMS experiments investigated the oxidative processing of particulate amines including octadecylamine and hexadecylamine. Ozonolysis of these amines resulted in strong NO2 - and NO3 - ion signals that increased with the ozone exposure and suggested a mechanism of progressive oxidation. Additionally, a strong ion signal was detected for NO3 -(HNO3), which is the ion core of the most important ion cluster series in the troposphere, NO3 -(HNO3)n(H2O)m. PERCI-AMS was applied to the analysis of ozonized mixed particles of amines with oleic acid or dioctyl sebacate. In the ozonolysis of the amines with oleic acid, products included imines and amides. The routes to the amides were shown to most likely arise from the reactivity of stabilized Criegee intermediates and/or secondary ozonides with the amines. There was also direct evidence of the formation of a surface barrier in the octadecylamine and oleic acid reaction system, which resulted in the retention of oleic acid at high ozone exposures. These experiments have fostered a better understanding of the analytical capacity of PERCI-AMS in assaying the reactivity of organic aerosols as well as giving a more accurate description of the heterogeneous chemistry of these challenging reaction systems. Suggestions for adaptations to PERCI-AMS and future experiments o

The ozonolysis of primary aliphatic amines in fine particles

International audienceThe oxidative processing by ozone of the particulate amines octadecylamine (ODA) and hexadecylamine (HDA) is reported. Ozonolysis of these amines resulted in strong NO2? and NO3? ion signals that increased with ozone exposure as monitored by photoelectron resonance capture ionization aerosol mass spectrometry. These products suggest a mechanism of progressive oxidation of the particulate amines to nitroalkanes. Additionally, a strong ion signal at 125 m/z is assigned to the ion NO3? (HNO3). For ozonized mixed particles containing ODA or HDA + oleic acid (OL), with pO3?3×10?7 atm, imine, secondary amide, and tertiary amide products were measured. These products most likely arise from reactions of amines with aldehydes (for imines) and stabilized Criegee intermediates (SCI) or secondary ozonides (for amides) from the fatty acid. The routes to amides via SCI and/or secondary ozonides were shown to be more important than comparable amide forming reactions between amines and organic acids, using azelaic acid as a test compound. Finally, direct evidence is provided for the formation of a surface barrier in the ODA + OL reaction system that resulted in the retention of OL at high ozone exposures (up to 10?3 atm for 17 s). This effect was not observed in HDA + OL or single component OL particles, suggesting that it may be a species-specific surfactant effect from an in situ generated amide or imine. Implications to tropospheric chemistry, including particle bound amines as sources of oxidized gas phase nitrogen species (e.g.~NO2, NO3), formation of nitrogen enriched HULIS via ozonolysis of amines and source apportionment are discussed

The ozonolysis of primary aliphatic amines in single and multicomponent fine particles

International audienceThe oxidative processing by ozone of the particulate amines octadecylamine (ODA) and hexadecylamine (HDA) is reported. Ozonolysis of these amines resulted in strong NO2? and NO3? ion signals that increased with ozone exposure as monitored by photoelectron resonance capture ionization aerosol mass spectrometry. These products suggest a mechanism of progressive oxidation of the particulate amines to nitro alkanes. Additionally, a strong ion signal at 125 m/z is assigned to the ion NO3?(HNO3). For ozonized mixed particles containing ODA or HDA + oleic acid (OL), with pO3?3×10?7 atm, imine, secondary amide, and tertiary amide products were measured. These products most likely arise from reactions of amines with aldehydes (for imines) and stabilized Criegee intermediates (SCI) or secondary ozonides (for amides) from the fatty acid. The routes to amides via SCI and/or secondary ozonides was shown to be more important than comparable amide forming reactions between amines and organic acids, using azelaic acid as a test compound. Finally, direct evidence is provided for the formation of a surface barrier in the ODA + OL reaction system that resulted in the retention of OL at high ozone exposures (up to 10?3 atm for 17 s). This effect was not observed in HDA + OL or single component OL particles, suggesting that it may be a species-specific surfactant effect from an in situ generated amide or imine. Implications to tropospheric chemistry, including particle bound amines as sources of oxidized gas phase nitrogen species (e.g. NO2, NO3), formation of nitrogen enriched HULIS via ozonolysis of amines and source apportionment are discussed

Near-infrared laser desorption/ionization aerosol mass spectrometry for measuring organic aerosol at atmospherically relevant aerosol mass loadings

A new method, near-infrared laser desorption/ionization aerosol mass spectrometry (NIR-LDI-AMS), is described for the real time analysis of organic aerosols at atmospherically relevant total mass loadings. Particles are sampled with an aerodynamic lens onto an aluminum probe. A moderate energy NIR laser pulse at 1064 nm is directed onto the probe to vaporize and ionize particle components. Delayed pulse extraction is then used to sample the ions into a reflectron time of flight mass spectrometer for chemical analysis. The soft ionization afforded by the NIR photons results in minimal fragmentation (loss of a hydrogen atom) producing intact pseudo-molecular anions at [M-H]<sup>−</sup>. The limit of detection measured for pure oleic acid particles (geometric mean diameter and standard deviation of 180 nm and 1.3, respectively) was 140 fg (or 1.7 ng m<sup>−3</sup> per minute sampling time). As an example of the utility of NIR-LDI-AMS to measurements of atmospheric importance, the method was applied to laboratory chamber measurements of the secondary organic aerosol formation from ozonolysis of α-pinene. High quality mass spectra were recorded with a 2-min time resolution for total aerosol mass loadings ranging from 1.5 to 8.7 μg m<sup>−3</sup>. These results demonstrate the potential of NIR-LDI-AMS to allow for more accurate measurements of the organic fraction of atmospheric particulate at realistic mass loadings. Measurements at ambient-levels of SOA mass loading are important to improve parameterizations of chamber-based SOA formation for modeling regional and global SOA fluxes and to aid in remediating the discrepancy between modeled and observed atmospheric total SOA production rates and concentrations

Shikimic acid ozonolysis kinetics of the transition from liquid aqueous solution to highly viscous glass

Ageing of particulate organic matter affects the composition and properties of atmospheric aerosol particles. Driven by temperature and humidity, the organic fraction can vary its physical state between liquid and amorphous solid, or rarely even crystalline. These transitions can influence the reaction kinetics due to limitations of mass transport in such (semi-) solid states, which in turn may influence the chemical ageing of particles containing such compounds. We have used coated wall flow tube experiments to investigate the reaction kinetics of the ozonolysis of shikimic acid, which serves as a proxy for oxygenated, water-soluble organic matter and can form a glass at room temperature. Particular attention was paid to how the presence of water influences the reaction, since it acts a plasticiser and thereby induces changes in the physical state. We analysed the results by means of a traditional resistor model, which assumes steady-state conditions. The ozonolysis rate of shikimic acid is strongly increased in the presence of water, a fact we attribute to the increased transport of O-3 and shikimic acid through the condensed phase at lower viscosities. The analysis using the resistor model suggests that the system undergoes both surface and bulk reaction. The second-order rate coefficient of the bulk reaction is 3.7 (+1.5/-3.2) x 10(3) L mol(-1) s(-1). At low humidity and long timescales, the resistor model fails to describe the measurements appropriately. The persistent O-3 uptake at very low humidity suggests contribution of a self-reaction of O-3 on the surface

Establishing the contribution of lawn mowing to atmospheric aerosol levels in American suburbs

Green leaf volatiles (GLVs) are a class of wound-induced volatile organic compounds emitted by several plant species. Turf grasses emit a complex profile of GLVs upon mowing, as evidenced by the "freshly cut grass" smell, some of which are readily oxidized in the atmosphere to contribute to secondary organic aerosol (SOA). The contribution of lawn-mowing-induced SOA production may be especially impactful at the urban–suburban interface, where urban hubs provide a source of anthropogenic oxidants and SOA while suburban neighborhoods have the potential to emit large quantities of reactive, mow-induced GLVs. This interface provides a unique opportunity to study aerosol formation in a multicomponent system and at a regionally relevant scale. Freshly cut grass was collected from a study site in Essex Junction, Vermont, and was placed inside a 775 L Teflon experimental chamber. Thermal desorption gas chromatography–mass spectrometry (TD-GC/MS) was used to characterize the emitted GLV profile. Ozone was introduced to the experimental chamber and TD-GC/MS was used to monitor the consumption of these GLVs and the subsequent evolution of gas-phase products, while a scanning mobility particle sizer was used to continuously measure aerosol size distributions and mass loadings as a result of grass clipping ozonolysis. Freshly cut grass was found to emit a complex mixture of GLVs, dominated by \textit{cis}-3-hexenyl acetate (CHA) and \textit{cis}-3-hexenol (HXL), which were released at an initial rate of 1.8 (± 0.5) μg and 0.07 (± 0.03) μg per square meter of lawn mowed with each mowing. Chamber studies using pure standards of CHA and HXL were found to have aerosol yields of 1.2 (± 1.1)% and 3.3 (± 3.1)%, respectively. Using these aerosol yields and the emission rate of CHA and HXL by grass, SOA evolution by ozonolysis of grass clippings was predicted. However, the measured SOA mass produced from the ozonolysis of grass clippings exceeded the predicted amount, by upwards of ~150%. The ozonolysis of a mixture of CHA and HXL representative of environmental mixing ratios also failed to accurately model the SOA mass produced by grass clippings. The disparity between measured SOA mass and the predicted SOA mass suggests that grass clippings contain other SOA precursors in addition to CHA and HXL. Aerial photographs and geospatial analysis were used to determine the area of turfgrass coverage in a suburban neighborhood, which was then used along with measured SOA production as a function of grass mowed to determine that lawn mowing has the potential to contribute 47 μg SOA per m−2 of lawn to the atmosphere per mowing event by ozonolysis, which cannot be modeled solely by the ozonolysis of CHA, HXL or a representative mixture of the two