Atmospheric transformation of monoterpenes gives products that may cause environmental consequences. In this work the NO3 radical-initiated oxidation of the monoterpenes α-pinene, β-pinene, Δ3-carene, and limonene has been investigated. All experiments were conducted in EUPHORE, the EUropean PHOto REactor facility in Valencia, Spain. The aerosol and product yields were measured in experiments with a conversion of the terpenes in the interval from 7 to 400 ppb. The lower end of the concentrations used are close to those measured in ambient pine forest air. Products were measured using long path in situ FTIR. Aerosol yields were obtained using a DMA-CPC system. The aerosol mass yields measured at low concentrations (10 ppb terpene reacted) were <1, 10, 15, and 17% for α-pinene, β-pinene, Δ3-carene, and limonene, respectively. The total molar alkylnitrate yields were calculated to be 19, 61, 66, and 48%, and molar carbonyl compound yields were estimated to be 71, 14, 29, and 69% for α-pinene, β-pinene, Δ3-carene, and limonene, respectively. The aerosol yields were strongly dependent on the amounts of terpene reacted, whereas the nitrate and carbonyl yields do not depend on the amount of terpene converted. The principal carbonyl compound from α-pinene oxidation was pinonaldehyde. In the case of limonene, endolim was tentatively identified and appears to be a major product. The reactions with β-pinene and Δ3-carene yielded 1−2% of nopinone and 2−3% caronaldehyde, respectively. The results show that it is not possible to use generalized descriptions of terpene chemistry, e.g. in matematical models.
Abstract. The effect of reaction temperature and how water vapour influences the formation of secondary organic aerosol (SOA) in ozonolysis of limonene, Δ3-carene and α-pinene, both regarding number and mass of particles, has been investigated by using a laminar flow reactor (G-FROST). Experiments with cyclohexane and 2-butanol as OH scavengers were compared to experiments without any scavenger. The reactions were conducted in the temperature range between 298 and 243 K, and at relative humidities between <10 and 80%. Results showed that there is still a scavenger effect on number and mass concentrations at low temperatures between experiments with and without an addition of an OH scavenger. This shows that the OH chemistry is influencing the SOA formation also at these temperatures. The overall temperature dependence on SOA formation is not as strong as expected from partitioning theory. In some cases there is even a positive temperature dependence that must be related to changes in the chemical mechanism and/or reduced rates of secondary chemistry at low temperatures. The precursor's α-pinene and Δ3-carene exhibit a similar temperature dependence regarding both number and mass of particles formed, whereas limonene shows a different dependence. The water effect at low temperature could be explained by physical uptake and cluster stabilisation. At higher temperatures, only a physical explanation is not sufficient and the observations are in line with water changing the chemical mechanism or reaction rates. The data presented adds to the understanding of SOA contribution to new particle formation and atmospheric degradation mechanisms.
Abstract. The heterogeneous oxidation of SO2 by NO2 on mineral dust was studied using Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS) and a Knudsen cell. This made it possible to characterise, kinetically, both the formation of sulfate and nitrate as surface products and the gas phase loss of the reactive species. The gas phase loss rate was determined to be first order in both SO2 and NO2. From the DRIFTS experiment the uptake coefficient, g , for the formation of sulfate was determined to be of the order of 10-10 using the BET area as the reactive surface area. No significant formation of sulfate was seen in the absence of NO2. The Knudsen cell study gave uptake coefficients of the order of 10-6 and 10-7 for SO2 and NO2 respectively. There was no significant difference in uptake when SO2 or NO2 were introduced individually compared to experiments in which SO2 and NO2 were present at the same time.
Rate coefficients for the reaction of acrolein (prop-2-en-1-al), crotonaldehyde (but-2-en-1-al) and pivalaldehyde (2,2-dimethylpropanal) with chlorine atoms were determined. The resulting rate coefficients were (1.8 ± 0.3) × 10−10, (2.2 ± 0.4) × 10−10 and (1.2 ± 0.2) × 10−10 (cm3 molecule−1 s−1) for acrolein, crotonaldehyde and pivalaldehyde, respectively. Rate coefficients for chlorine atom reaction with propanal, butanal, 2-methylpropanal and trans-but-2-ene were determined to be (1.2 ± 0.2) × 10−10, (1.5 ± 0.3) × 10−10, (1.5 ± 0.3) × 10−10 and (3.0 ± 0.6) × 10−10 (cm3 molecule−1 s−1), respectively. The relative rate technique was used with propene as the reference compound. The experiments were carried out at 297 ± 2 K and 1020 ± 2 mbar using a 0.153 m3 borosilicate glass reactor with long-path FTIR spectroscopy as the analytical tool. Synthetic air and nitrogen were used as bath gases. Literature values of the corresponding hydroxyl and nitrate radical rate coefficients were confirmed. The chemical characteristics of the organic substances have a limited influence on the reactivity with Cl, a larger effect in the OH-case but are decisive for the NO3 reactions. Introduction of an aldehydic carbonyl group into an unsaturated compound reduces the reactivity of a neighboring double bond for reaction with all three radicals. The unsaturated aldehydes reacting with NO3 show a rate coefficient that is lower than both the corresponding simple alkene and aliphatic aldehyde, indicating that also the reactivity of the aldehydic hydrogen atom is affected. The results show that during the morning hours, Cl atoms may be the most significant oxidising agent for organic substances in urban coastal air.
Rate coefficients for the reactions between NO 3 and the chloroethenes have been determined by the fast-flow-discharge technique and by the relative rate method in a static reactor employing FTIR detection. The relative rate experiments were performed at 298 ± 2 K and 1013 ± 3 mbar in a nitrogen atmosphere with excess ethane as a chlorine scavenger. The flow tube experiments were carried out under pseudo-first-order conditions in NO 3 . The temperature dependence of the NO 3 reactions with chloroethene and trichloroethene was investigated over a temperature range of ca. 100 K, and their rate coefficients were fitted to Arrhenius expressions. A comparison between our measured rate coefficient data for the NO 3 reaction with chloroethenes reveals that the relative rate results are up to 20% lower than those from the fast-flow-discharge experiments. Possible secondary reactions in the flow tube are discussed.
