In this paper, a kinetic study of the oxidation of maleic and fumaric acid organic particles by gas-phase ozone at relative humidities ranging from 90 to 93% is reported. A flow of single component aqueous particles with average size diameters in the range 2.6–2.9 µm were exposed to a known concentration of ozone for a controlled period of time in an aerosol flow tube in which products were monitored by infrared spectroscopy. The results obtained are consistent with a Langmuir–Hinshelwood type mechanism for the heterogeneous oxidation of maleic/fumaric acid aerosol particles by gas-phase ozone, for which the following parameters were found: for the reaction of maleic acid aerosols, KO3 = (9 ± 4) × 10−15 cm3 molecule−1 and kImax = (0.21 ± 0.01) s−1; for the reaction of fumaric acid aerosols, KO3 = (5 ± 2) × 10−15 cm3 molecule−1 and kImax = (0.19 ± 0.01) s−1. From the pseudo-first-order coefficients, apparent uptake coefficient values were calculated for which a decreasing trend with increasing ozone concentrations was observed. Comparison with previous measurements of the same system under dry conditions reveals a direct effect of the presence of water on the mechanism of these reactions, in which the water is seen to increase the formation of CO2 and formic acid (HCO2H) through increased levels of hydroxyacetyl hydroperoxide intermediate.

In this paper, the heterogeneous reaction between oleic acid and ozone has been studied using infrared spectroscopy in two distinctly different experimental configurations. The effect of the experiment on the observed products and rates of reaction is compared in order to derive a better understanding of some of the variations in oleic acid reaction rates reported by a range of researchers. One set of measurements is made using thin films of oleic acid in an attenuated total internal reflection configuration, and it is shown that a treatment in which the ATR evanescent wave is convolved with a moving reaction front is essential for the extraction of reliable kinetic data. The results are compared to similar measurements in a recently developed aerosol flow tube equipped with a cross-beam infrared spectroscopic probe. Rates of reaction in the aerosol phase are observed to be approximately 10 times faster and possible reasons for this discussed.

In this paper, infrared spectroscopic and mass spectrometric studies of the ozonolysis of some simple proxies of precursors to organic materials found in atmospheric aerosols is reported. Oleic and maleic acids are used as proxies of reactive material, containing unsaturation which is amenable to ozonolysis. Nonanoic acid and benzoic acid are utilised as co-reactants which, although not likely to undergo direct ozonolysis themselves, are potential reaction partners to the Criegee radical intermediates formed from oleic and maleic acid ozonolysis. The precursor species are studied as single components in solution, followed by co-reaction studies. The products of the ozonolysis are followed by mass spectrometry and infrared spectroscopy. The product distributions from oleic and maleic acid are broadly in agreement with those observed in other studies. In the co-reaction studies, new evidence for cross-reaction products is obtained. Furthermore, the nature of some of the products does not fully comply with the widely accepted Ziemann scheme.

Dicarboxylic acids, either directly emitted or formed in chemical processes, are found to be a significant component of tropospheric aerosols. To assess any potential chemical transformation of short unsaturated dicarboxylic acids in tropospheric heterogeneous chemistry, maleic and fumaric acid were selected as surrogates in this study. A novel aerosol flow tube apparatus is employed to perform kinetic studies of the oxidation of these organic compounds by gas-phase ozone. The system consists of a particle generation system, a vertically oriented glass flow tube and an infrared observation White cell with a Fourier transform infrared (FTIR) spectrometer for the detection system. A flow of single component organic aerosols with mean diameters ranging between 0.7 and 1.1 μm is introduced in a flow tube, in which the particles are subsequently exposed to a known concentration of ozone for a controlled period of time. A band assignment of infrared vibrational frequencies for dry maleic and fumaric acid aerosol spectra is presented. These studies are complemented with off-line analysis on the reaction products. The reaction exhibited pseudo-first-order kinetics on gas product formation, and the pseudo-first-order rate coefficients displayed a Langmuir–Hinshelwood dependence on gas-phase ozone concentration for both materials. By assuming a Langmuir–Hinshelwood behaviour, the following parameters were obtained: for the reaction of maleic acid aerosols, KO3 = (3.3 + 0.5) × 10−16 cm3 molecule−1 and kImax = (0.038 + 0.004) s−1; for the reaction of fumaric acid aerosols, KO3 = (1.6 + 0.5) × 10−16 cm3 molecule−1 and kImax = (0.048 + 0.007) s−1, where KO3 is a parameter that describes the partitioning of ozone to the particle surface and kImax is the maximum pseudo-first-order coefficient at high ozone concentrations. Apparent reactive uptake coefficients were estimated from the pseudo-first-order rate coefficient and a trend of decreasing uptake coefficients with increasing ozone concentrations was observed, in good agreement with literature values.

Soot samples as potential mimics of atmospheric aerosols have been produced from the combustion of toluene, kerosene and diesel in order to compare the nature of soot produced from a simpler material, toluene, with soots from the fuels kerosene and diesel. Characterisation of the soots using elemental analysis, infrared spectroscopy, solvent extraction, thermal desorption and electron microscopy techniques before and after reaction with ozone allows assessment of the reactivity of soots from these different fuels. Despite the production of toluene and kerosene soots from identical combustion conditions, strong differences in structure and reactivity are observed in terms of their reaction with ozone. However, toluene soot is a much better mimic of diesel soot. It is proposed that the differing reactivities of the soots is related to the nature of the organic carbon and structure of the elemental carbon which vary with soots from the different fuels.

Soot samples as potential mimics of atmospheric aerosols have been produced from the combustion of toluene, kerosene and diesel in order to compare the nature of soot produced from a simpler material, toluene, with soots from the fuels kerosene and diesel. Characterisation of the soots using elemental analysis, infrared spectroscopy, solvent extraction, thermal desorption and electron microscopy techniques before and after reaction with ozone allows assessment of the reactivity of soots from these different fuels. Despite the production of toluene and kerosene soots from identical combustion conditions, strong differences in structure and reactivity are observed in terms of their reaction with ozone. However, toluene soot is a much better mimic of diesel soot. It is proposed that the differing reactivities of the soots is related to the nature of the organic carbon and structure of the elemental carbon which vary with soots from the different fuels.

Dicarboxylic acids, either directly emitted or formed in chemical processes, are found to be a significant component of tropospheric aerosols. To assess any potential chemical transformation of short unsaturated dicarboxylic acids in tropospheric heterogeneous chemistry, maleic and fumaric acid were selected as surrogates in this study. A novel aerosol flow tube apparatus is employed to perform kinetic studies of the oxidation of these organic compounds by gas-phase ozone. The system consists of a particle generation system, a vertically oriented glass flow tube and an infrared observation White cell with a Fourier transform infrared (FTIR) spectrometer for the detection system. A flow of single component organic aerosols with mean diameters ranging between 0.7 and 1.1 μm is introduced in a flow tube, in which the particles are subsequently exposed to a known concentration of ozone for a controlled period of time. A band assignment of infrared vibrational frequencies for dry maleic and fumaric acid aerosol spectra is presented. These studies are complemented with off-line analysis on the reaction products. The reaction exhibited pseudo-first-order kinetics on gas product formation, and the pseudo-first-order rate coefficients displayed a Langmuir–Hinshelwood dependence on gas-phase ozone concentration for both materials. By assuming a Langmuir–Hinshelwood behaviour, the following parameters were obtained: for the reaction of maleic acid aerosols, KO3 = (3.3 + 0.5) × 10−16 cm3 molecule−1 and kImax = (0.038 + 0.004) s−1; for the reaction of fumaric acid aerosols, KO3 = (1.6 + 0.5) × 10−16 cm3 molecule−1 and kImax = (0.048 + 0.007) s−1, where KO3 is a parameter that describes the partitioning of ozone to the particle surface and kImax is the maximum pseudo-first-order coefficient at high ozone concentrations. Apparent reactive uptake coefficients were estimated from the pseudo-first-order rate coefficient and a trend of decreasing uptake coefficients with increasing ozone concentrations was observed, in good agreement with literature values.

In this paper, infrared spectroscopic and mass spectrometric studies of the ozonolysis of some simple proxies of precursors to organic materials found in atmospheric aerosols is reported. Oleic and maleic acids are used as proxies of reactive material, containing unsaturation which is amenable to ozonolysis. Nonanoic acid and benzoic acid are utilised as co-reactants which, although not likely to undergo direct ozonolysis themselves, are potential reaction partners to the Criegee radical intermediates formed from oleic and maleic acid ozonolysis. The precursor species are studied as single components in solution, followed by co-reaction studies. The products of the ozonolysis are followed by mass spectrometry and infrared spectroscopy. The product distributions from oleic and maleic acid are broadly in agreement with those observed in other studies. In the co-reaction studies, new evidence for cross-reaction products is obtained. Furthermore, the nature of some of the products does not fully comply with the widely accepted Ziemann scheme.

In this paper, the heterogeneous reaction between oleic acid and ozone has been studied using infrared spectroscopy in two distinctly different experimental configurations. The effect of the experiment on the observed products and rates of reaction is compared in order to derive a better understanding of some of the variations in oleic acid reaction rates reported by a range of researchers. One set of measurements is made using thin films of oleic acid in an attenuated total internal reflection configuration, and it is shown that a treatment in which the ATR evanescent wave is convolved with a moving reaction front is essential for the extraction of reliable kinetic data. The results are compared to similar measurements in a recently developed aerosol flow tube equipped with a cross-beam infrared spectroscopic probe. Rates of reaction in the aerosol phase are observed to be approximately 10 times faster and possible reasons for this discussed.

In this paper, a kinetic study of the oxidation of maleic and fumaric acid organic particles by gas-phase ozone at relative humidities ranging from 90 to 93% is reported. A flow of single component aqueous particles with average size diameters in the range 2.6–2.9 µm were exposed to a known concentration of ozone for a controlled period of time in an aerosol flow tube in which products were monitored by infrared spectroscopy. The results obtained are consistent with a Langmuir–Hinshelwood type mechanism for the heterogeneous oxidation of maleic/fumaric acid aerosol particles by gas-phase ozone, for which the following parameters were found: for the reaction of maleic acid aerosols, KO3 = (9 ± 4) × 10−15 cm3 molecule−1 and kImax = (0.21 ± 0.01) s−1; for the reaction of fumaric acid aerosols, KO3 = (5 ± 2) × 10−15 cm3 molecule−1 and kImax = (0.19 ± 0.01) s−1. From the pseudo-first-order coefficients, apparent uptake coefficient values were calculated for which a decreasing trend with increasing ozone concentrations was observed. Comparison with previous measurements of the same system under dry conditions reveals a direct effect of the presence of water on the mechanism of these reactions, in which the water is seen to increase the formation of CO2 and formic acid (HCO2H) through increased levels of hydroxyacetyl hydroperoxide intermediate.