P. Carlier

Carboxylic acids in the troposphere, occurrence, sources, and sinks: A review

Abstract Carboxylic acids are ubiquitous and important components of the troposphere; they are currently measured in different environments. They are thought to have several sources comprising primary biogenic and anthropogenic emissions, hydrocarbons gas-phase oxidations, and some carbonyl compounds aqueous-phase oxidations. In the present review we make a synthesis of the concentrations of low molecular weight carboxylic acids in tropospheric aqueous and gaseous phases and in aerosol particles for different environments. We also successively examine the major sources of carboxylic acids and discuss their relative contribution to tropospheric concentrations for various environments as well as the principal sinks of these compounds.

The chemistry of carbonyl compounds in the atmosphere—A review

Abstract Carbonyl compounds are very important for the trophospheric physico-chemistry because they are the result of the first photo-oxidation stage of almost all organic compounds and they are the essential originators of the free radicals. In the present review we make a synthesis of the studies on the carbonyl compounds chemistry in the trophosphere by successively examining: measurement methods in the trophosphere, sources of primary carbonyl compounds, formation of secondary carbonyl compounds in the atmosphere, reactivity of carbonyl compounds in the atmosphere.

Field studies of aldehyde chemistry in the Paris area

Abstract Measurements of carbonyl compound concentrations at different sites in the Paris area have been carried out. Interpretation of the results made use of the following data: general meteorological conditions, wind field analysis and type of primary pollutant sources. The principal phenomena observed were: a sharp formaldehyde decrease during rainfall; concentration levels of lower aldehydes in rural sites comparable to those found in the literature; an important variation in the ratio of primary aldehydes to secondary aldehydes depending on meteorological conditions; a significant increase in lower aldehyde concentrations downwind from the urban center despite vertical dispersion of the pollutants.

KINETICS OF THE REACTIONS OF OH RADICALS WITH SOME OXYGENATED VOLATILE ORGANIC COMPOUNDS UNDER SIMULATED ATMOSPHERIC CONDITIONS

Some relative rate experiments have been carried out at room temperature and at atmospheric pressure. This concerns the OH-oxidation of some oxygenated volatile organic compounds including methanol (k1), ethanol (k2), MTBE (k3), ethyl acetate (k4), n-propyl acetate (k5), isopropyl acetate (k6), n-butyl acetate (k7), isobutyl acetate (k8), and t-butyl acetate (k9). The experiments were performed in a Teflon-film bag smog chamber. The rate constants obtained are (in cm3 molecule−1 s−1): k1=(0.90±0.08)×10−12; k2=(3.88±0.11)×10−12; k3=(2.98±0.06)×10−12; k4=(1.73±0.20)×10−12; k5=(3.56±0.15)×10−12; k6=(3.97±0.18)×10−12; k7=(5.78±0.15)×10−12; k8=(6.77±0.30)×10−12; and k9=(0.56±0.11)×10−12. The agreement between the obtained rate constants and some previously published data has allowed for most of the studied compounds to point out a coherent group of values and to suggest recommended values. Atmospheric implications are also discussed.

Origins of Atmospheric Particulate Matter over the North Sea and the Atlantic Ocean

During the ANT VII/1 cruise of the RV Polarstern from Bremerhaven (Germany) to Rio Grande do Sul (Brazil), atmospheric particulate matter was collected by bulk filtration with a time step of 36 hours. Elemental analyses were performed in order to determine atmospheric aerosol concentrations of Al, Si, P, S, K, Ca, Ti, Mn, Fe, and Zn over the North Sea, the Channel, and the North and South Atlantic. The slight and continuous moving in latitude, associated with the large variability in concentration levels and chemical composition, allow us to point out the relative influence of the major sources of particulate matter: desert soil-dust in the tropical North Atlantic, anthropogenic emissions in the North Sea and the Channel, and biomass burning and continental biogenic activity in the tropical South Atlantic.

FTIR spectroscopic study of the OH-induced oxidation of two linear acetates: ethyl and n-propyl acetates

OH-induced oxidation mechanisms of ethyl and n-propyl acetates have been investigated at room temperature (298 ± 5 K) and atmospheric pressure by photolysing CH3ONO/acetate/NO mixtures with FTIR spectroscopy as analytical device. The main oxidation products and their yields were as follows: from ethyl acetate, acetic acid (0.75 ± 0.13), acetoxyacetaldehyde (0.15 ± 0.05), acetic anhydride (0.02 ± 0.01), formic acetic anhydride (0.02 ± 0.01) and peroxyacetyl nitrate (PAN); from n-propyl acetate, acetoxyacetaldehyde (0.22 ± 0.06), formic acetic anhydride (0.28 ± 0.03), acetic acid (0.15 ± 0.02), acetaldehyde (0.35 ± 0.10), peroxypropionyl nitrate (PPN) and probably acetoxypropionaldehyde (0.30 ± 0.10). From these data, oxidation schemes of these two acetates were elucidated. This study reveals in particular the specific reactivity of acetates by confirming the novel α-ester rearrangement proposed recently by Tuazon et al. (J. Phys. Chem. A, 1998, 102, 2316) and then by showing that oxygenated alkoxyl radicals may not follow the same rules of reactivity as other alkoxyl radicals. This last observation shows the necessity for further experiments to understand the influence of the oxygenated function on alkoxyl reactivity.

Atmospheric fate of alkoxy radicals: branching ratio of evolution pathways for 1-propoxy, 2-propoxy, 2-butoxy and 3-pentoxy radicals

As the last step of VOC oxidation in the atmosphere, the evolution of alkoxy radicals determines the nature and the concentration of the secondary compounds formed. Branching ratios between decomposition and reaction with O2 of 1-propoxy, 2-propoxy, 2-butoxy and 3-pentoxy radicals have been measured at room temperature and atmospheric pressure in a simulation chamber using FTIR spectroscopy as an analytical device. kdec/kO2 is equal to (3.8 ± 0.4) × 1016, (2.9 ± 0.3) × 1016, (2.9 ± 0.4) × 1018 and (4.1 ± 0.8) × 1018 molecules cm−3 for each, respectively. This ratio has been observed to vary, depending on the leaving alkyl group and the class of alkoxy. No additional decomposition due to excited radicals has been observed.

Laboratory investigation of the photooxidation of formaldehyde combining FTIR analysis of stable species and HO2 detection by the chemical amplifier technique

Abstract The photodissociation of formaldehyde in air at one atmosphere pressure and room temperature has been investigated in a 977 L photoreactor by in situ analysis of stable species by FTIR absorption spectroscopy and of peroxy radicals, HO 2 , by the chemical amplifier technique, after sampling. The photodissociation coefficient of the channel H 2 CO+ hν (+O 2 ) → 2 HO 2 +CO (1) determined experimentally was found consistent with that calculated from the absorption spectrum of H 2 CO and the spectral distribution of the photolysis light. The rate constant k −3 of the thermal decomposition of the adduct formed in the reaction HO 2 +H 2 CO↔HOCH 2 O 2 (3, −3) was determined and found at the lower limit of the range of the literature values. This study confirms the potentiality of the chemical amplifier technique in combination with other analytical techniques to investigate chemical mechanisms of atmospheric interest in photoreactors.

Photo-Induced OH reactions of naphthalene and its oxidation products on SiO2

The photo-induced degradation of naphthalene, 1,4-naphthoquinone, 1-naphthol and 1-NO2 naphthalene, adsorbed on silica gel, and with the addition of nitrogenous air pollutants e.g. NO2 (as KNO2) was investigated. Results indicate that compounds adsorbed onto a solid carrier are degraded when irradiated with UV light (λ > 290 nm) in the presence of nitrites. The key species initiating the naphthalene degradation is the OH-radical which is generated through the photolysis of NO2. Reaction products identified were 2-formyl-cinnamaldehyde, 1,4-naphthoquinone, nitronaphthol, o-phthaldialdehyde, phthalide and nitronaphthalene. A mass balance between 40–50% was achieved. Under the same irradiation conditions, 1-NO2 naphthalene is mainly degraded by direct photolysis while degradation of 1-naphthol and 1,4-naphthoquinone proceeds via the reaction with OH-radicals. Identified products were hydroxy-nitro-nitroso- and quinones compounds.

Formaldehyde Background Levels over the Atlantic Ocean during the Polarstern Crossing from Bremerhaven to Rio Grande Do Sul

During the POLASTERN crossing from Bremerhaven to Rio Grande do sul (15 september to 9 october 1988) we have measured the formaldehyde atmospheric concentrations at about 30 m above the ocean. The used experimental technique is the very same that we have used during the campaign at the “pointe de Penmarc’h” in July 1988. Outside of the area under continental influence the average levels are 0,4 ppbv in the north hemisphere, 0,3 ppbv in the south hemisphere and about 2 ppbv in the intertropical convergence zone. While the main values observed outside the ITCZ are in agreement with those expected from the methane oxidation and the formaldehyde photochimical depletion, these obtained in the ITCZ can only be explained by taking into account the relative high concentrations of alcenes found in this area and their fast oxidation.