Search

An experimental study on the 3-chloro-2-methyl-1-propene (CMP), 2,3-dichloropropene (DCP) and 3,4-dichlorobutene (DCB) reactions with atmospheric oxidants at (298 ± 1) K and atmospheric pressure is reported. Rate constants for the gas phase reactions of the three chlorinated alkenes with O3, OH and NO3 radicals and Cl atom were determined in a 100 L Teflon reactor by gas chromatography with flame ionization detector (GC-FID). The obtained rate constants are (3.03 ± 0.15) × 10−18, (3.83 ± 1.30) × 10−11, (1.99 ± 0.19) × 10−14, and (2.40 ± 0.41) × 10−10 cm3 molecule−1 s−1 for CMP reactions with O3, OH, NO3, and Cl, respectively, (4.62 ± 1.41) × 10−20, (1.37 ± 1.02) × 10−11, (1.45 ± 0.15) × 10−15 and (1.30 ± 0.99) × 10−11 cm3 molecule−1 s−1 for DCP reactions and (2.09 ± 0.24) × 10−19, (1.45 ± 0.59) × 10−11, (3.00 ± 0.82) × 10−16 and (1.91 ± 0.19) × 10−10 cm3 molecule−1 s−1 for DCB reactions. The CMP reaction products were detected and possible reaction mechanisms of their formation were proposed. Chloroacetone was found to be the major product in all four oxidation reactions. The loss process of CMP in the atmosphere is mostly controlled by its reaction with the OH radical during daytime and with NO3 during nighttime, with lifetimes of 3.6 h and 27.9 h respectively. Atmospheric implications of both these reactions and their potential products are discussed.

Size-resolved effective density, mixing state, and hygroscopicity of smoke particles from five kinds of agricultural residues burning were characterized using an aerosol chamber system, including a volatility/hygroscopic tandem differential mobility analyzer (V/H-TDMA) combined with an aerosol particle mass analyzer (APM). To profile relationship between the thermodynamic properties and chemical compositions, smoke PM1.0 and PM2.5 were also measured for the water soluble inorganics, mineral elements, and carbonaceous materials like organic carbon (OC) and elemental carbon (EC). Smoke particle has a density of 1.1–1.4 g cm−3, and hygroscopicity parameter (κ) derived from hygroscopic growth factor (GF) of the particles ranges from 0.20 to 0.35. Size- and fuel type-dependence of density and κ are obvious. The integrated effective densities (ρ) and hygroscopicity parameters (κ) both scale with alkali species, which could be parameterized as a function of organic and inorganic mass fraction (forg & finorg) in smoke PM1.0 and PM2.5: ρ − 1 = f i n o r g · ρ i n o r g − 1 + f o r g · ρ o r g − 1 and κ = f i n o r g · κ i n o r g + f o r g · κ o r g . The extrapolated values of ρinorg and ρorg are 2.13 and 1.14 g cm−3 in smoke PM1.0, while the characteristic κ values of organic and inorganic components are about 0.087 and 0.734, which are similar to the bulk density and κ calculated from predefined chemical species and also consistent with those values observed in ambient air. Volatility of smoke particle was quantified as volume fraction remaining (VFR) and mass fraction remaining (MFR). The gradient temperature of V-TDMA was set to be consistent with the splitting temperature in the OC-EC measurement (OC1 and OC2 separated at 150 and 250 °C). Combing the thermogram data and chemical composition of smoke PM1.0, the densities of organic matter (OM1 and OM2 correspond to OC1 and OC2) are estimated as 0.61–0.90 and 0.86–1.13 g cm−3, and the ratios of OM1/OC1 and OM2/OC2 are 1.07 and 1.29 on average, indicating more volatile organic materials have less density and lower OM/OC ratios in the external mixed smoke particles.

International audience; Unsaturated esters are emitted into the atmosphere from biogenic and anthropogenic sources. Their atmospheric degradation through reactions with the main atmospheric oxidants (OH, O3, NO3, Cl) contributes to the formation of important secondary pollutants. Kinetic and mechanistic parameters for these reactions are highly required in order to estimate the atmospheric lifetimes and hence the impacts of these important classes of VOCs. In this study, the gas-phase rate coefficients of the reaction of OH radical and O3 with a series of unsaturated esters are reported. The esters investigated include methyl methacrylate (MMA), ethyl methacrylate (EMA), n-propyl methacrylate (nPMA), n-butyl methacrylate (nBMA), iso-propyl methacrylate (iPMA), iso-butyl methacrylate (iBMA) and fully deuterated methyl methacrylate (MMA-D8). The measurement combined the pulsed laser photolysis-laser induced fluorescence for the OH studies in the temperature range 257–376K and a 7300 L atmospheric simulation chamber for the O3 reactions at 291 ± 2K. This work provides the first temperature-dependence studies of OH reaction with EMA, nPMA, iPMA and iBMA and of O3 reaction with nPMA, iPMA and iBMA at room temperature. The obtained data are discussed in terms of the structure reactivity relationships and their atmospheric consequences by estimating the atmospheric lifetimes for the studied esters with respect to O3, OH radical and other oxidant in the troposphere.

SSCI-VIDE+CARE+ABO:YDU:CGO; International audience; Emission factors (EFs) of pollutants emitted by light-duty vehicles (LDV) were investigated in the Leopold II tunnel in Brussels city center (Belgium), in September 2011 and in January 2013, respectively. Two sampling sites were housing the instruments for the measurements of a large range of air pollutants, including non-methane volatile organic compounds (NMVOCs), nitrogen oxides (NOx) and carbon dioxide (CO2). The NMVOCs and NOx traffic EFs for LDV were determined from their correlation with CO2 using a single point analysis method.The emission factor of NOx is (544 ± 199) mg vehicle−1 km−1; NMVOCs emission factors vary from (0.26 ± 0.09) mg vehicle−1 km−1 for cis-but-2-ene to (8.11 ± 2.71) mg vehicle−1 km−1 for toluene. Good agreement is observed between the EFs determined in the Leopold II tunnel and the most recent EFs determined in another European roadway tunnel in 2004, with only a slight decrease of the EFs during the last decade. An historical perspective is provided and the observed trend in the NMVOCs emission factors reflect changes in the car fleet composition, the fuels and/or the engine technology that have occurred within the last three decades in Europe.

The evolution in the dark of physiochemical properties and chemical composition of smoke particles emitted from wheat straw burning, as well as the effect of relative humidity (RH) on these properties, was investigated in an aerosol chamber. The smoke particles are composed primarily of carbonaceous materials and a considerable amount of inorganic salts (∼25 wt.%). During aging, the fraction of inorganic salts in smoke PM 1.0 increases, mainly due to the formation of more sulfate and nitrate at the expense of chloride; this heterogeneous conversion is facilitated at high RH. The hygroscopicity parameter κ H of fresh smoke particles is 0.27 and this is estimated to decrease by 0.01 after 4 h dark aging. Both aging and high RH lead to increases of particle size and density. The effective densities of smoke PM 2.5 and PM 1.0 deduced from concurrent mass and volume concentration measurements gradually increase from about 1.18 to 1.44 g/m 3 within 4 h aging at 45%–55% RH, in line with the results obtained both from size-resolved particle density analysis using an aerosol particle mass analyzer (APM) and from estimation using composition-weighted bulk densities. The density of smoke particle is size-, RH-, and aging extent-dependent; the size effect becomes less pronounced with aging.

International audience; Carbonyls are an important class of oxygenated volatile organic compounds that play a crucial role in tropospheric chemistry as intermediates in the formation of ozone (O3) and secondary organic aerosols. Over the last two decades, China's severe air pollution has led atmospheric chemists to devote substantial efforts to investigate the contribution of carbonyl compounds to the observed phenomena. This study reviews the major findings with regard to the gas-phase atmospheric chemistry of carbonyls in China, including their chemical compositions, temporal and spatial distributions, source apportionments, photochemical formation mechanisms, and impact on tropospheric oxidative capacity, air quality, and human health. Extremely high levels of carbonyls have frequently been observed in China's most rapidly developing regions, such as the North China Plain, the Yangtze River Delta, and the Pearl River Delta, but observational data from other regions are relatively scarce. Primary emissions and photochemical formation are major sources of carbonyls. Alkenes, aromatics, and isoprene have been identified as major precursors on a national scale. In addition, an increasing number of studies has focused on the effects of carbonyls on O3 formation, radical chemistry, the formation of secondary organic aerosols, and human health. The photolysis of oxygenated volatile organic compounds was recognized as a dominant pathway to ROx production, which further influences O3 formation, mainly via HO2+NO or RO2+NO. Dicarbonyls (such as glyoxal and methylglyoxal) make important contributions to secondary organic aerosol formation via irreversible uptake by aqueous particles. Indoor and outdoor carbonyls often pose a significant threat to human health. This review also includes recommendations from the perspective of emissions, observations, photochemical formation mechanisms, and the effects of carbonyls to guide future research and provide scientific support for the formulation of mitigation policies to address photochemical air pollution.

International audience; Field measurements were conducted to determine indoor air particulate pollutant emissions from the burning of coal and wood, two major household fuels, in rural households in Guizhou, China. Chemical composition, particle mass and particle size distribution as well as number concentration were measured in this study. Chemical composition analysis indicates that the carbonaceous particle is dominant in the PM2.5 mass, accounting for about 41% for wood and 55% for coal. The OC/EC ratio was 10.8 for wood and 7.6 for coal. Most of the water-soluble ions were found in the 0.4–2.1 μm size fractions and dominated by ammonium and sulfate. Particle mass concentrations inversely correlate with particle total number concentrations during the sampling period. Obvious differences were observed in the evolution of particle number concentrations and size distributions between coal combustion and wood burning. Particles emitted from coal combustion were characterized by unimodal size distribution, with average peak values ranging from 70.3 to 75.7 nm during the flaming stage of the burning cycle. Particles from wood burning were characterized by a transition from a bimodal size distribution to a unimodal distribution during the same period. Average peak values in the bimodal mode were 10–20 nm (nucleation mode) and 40–50 nm (Aitken mode), whereas the average peak value in the unimodal mode was about 63 nm.

The gas-phase degradation of hymexazol (5-methylisoxazol-3-ol), a widely used fungicide, was investigated under atmospheric conditions at the European Photoreactor (EUPHORE) in Valencia, Spain, a large outdoor simulation chamber. The rate coefficient for the reaction of hydroxyl radicals with hymexazol was measured using a conventional relative rate technique. A value of the rate coefficient for the reaction of OH radicals with hymexazol, k OH (hymexazol) = (4.9 ± 0.4) × 10 −12 cm 3 molecule −1 s −1 was determined at 300 ± 5 K and atmospheric pressure. Rate coefficient data for the reaction of OH radicals with isoxazole, the unsubstituted analogue of hymexazol, was also obtained using the relative rate method, k OH (isoxazole) = (1.1 ± 0.1) × 10 −12 cm 3 molecule −1 s −1 . The rate coefficients for photolysis of hymexazol, J (hymexazol) −6 s −1 , and reaction of ozone with hymexazol, k O 3 (hymexazol) = (3.2 ± 0.6) × 10 −19 cm 3 molecule −1 s −1 , under atmospheric conditions were also determined. The results showed that removal of hymexazol from the atmosphere by photolysis or by reaction with ozone is slow compared to loss by reaction with OH radicals. The available kinetic data suggest that the gas-phase tropospheric degradation of hymexazol will be mainly controlled by reaction with OH and possibly NO 3 radicals. The data provide the basis of an estimate for the tropospheric lifetime of approximately 1 day. The atmospheric implications of the use of hymexazol as a fungicide are discussed.

Ambient air samples were collected, from 2006 to 2008 at three rural and two urban sites in Centre Region (France) and analyzed for 56 currently used pesticides (CUPS), of which 41 were detected. The four CUPs most frequently detected were the herbicides trifluralin, acetochlor and pendimethalin and the fungicide chlorothalonil, which were found with frequencies ranging between 52 and 78%, and with average concentrations of 1.93, 1.32, 1.84 and 12.15 ng m(-3), respectively. Among the detected pesticides, concentrations of eight fungicides (spiroxamine, fenpropimorph, cyprodinil, tolyfluanid, epoxiconazole, vinchlozolin, fluazinam, fludioxinil), two insecticides (propargite, ethoprophos), and one herbicide (oxyfluorfen) are, to our knowledge, reported for the first time in the literature. The majority of the CUPs showed a seasonal trend, with most of the detections and the highest concentrations occurring during the spring and early summer. The most important pesticides detected were related to arable crops and fruit orchards, the main cultures in this region, highlighting the fact that the main sources come from local applications. Minor differences were found in the profiles of pesticides within rural areas and between rural and urban areas. (C) 2010 Elsevier Ltd. All rights reserved.

Rate constants for the reaction of OH radicals with n-propyl vinyl ether (PVE, CH3CH2CH2OCH CH2), n-butyl vinyl ether (BVE, CH3CH2CH2CH2OCH CH2), iso-butyl vinyl ether (IBVE, (CH3)2CHCH2OCH CH2) and tert-butyl vinyl ether (TBVE, (CH3)3COCH CH2), have been measured in the temperature and pressure ranges 232–373 K and 30–300 Torr using the pulsed laser photolysis-laser-induced fluorescence method, and at 298 K and 760 Torr using the relative method. The obtained results are k1=(9.3±0.6)×10−12 exp[(708±20)/T], k2=(1.5±0.2)×10−11 exp[(572±42)/T], k3=(1.6±0.1)×10−11 exp[(567±20)/T], k4=(1.7±0.2)×10−11 exp[(549±25)/T] cm3 molecule−1 s−1. The values at 298 K are k1=(1.0±0.1)×10−10, k2=(1.0±0.1)×10−10, k3=(1.1±0.1)×10−10, k4=(1.1±0.1)×10−10 cm3 molecule−1 s−1. The deduced tropospheric lifetimes of these ethers for reaction with OH are of the order of 1 h and they are comparable to those for reaction with ozone.

Absolute rate coefficients have been determined for the gas-phase reactions of hydroxyl radicals with methyl acrylate (k1), methyl methacrylate (k2) and ethyl acrylate (k3). Experiments were performed using two different techniques, the relative rate method and the pulsed laser photolysis-laser induced fluorescence technique. The kinetic data obtained were used to derive the following Arrhenius expressions in the temperature range 253–374 K (in units of cm3 molecule−1 s−1): k 1 = ( 2.0 ± 0.8 ) × 1 0 - 12 exp [ ( 553 ± 51 ) / T ] , k 2 = ( 2.5 ± 0.8 ) × 1 0 - 12 exp [ ( 821 ± 55 ) / T ] , k 3 = ( 2.3 ± 0.8 ) × 1 0 - 12 exp [ ( 580 ± 65 ) / T ] . At 298 K, the reaction rate constants obtained by the two methods were in good agreement. In addition, the UV absorption spectra for the three unsaturated esters have been determined at (298±2) K and the absorption cross-sections in the wavelength region 215–298 nm were reported. The results are presented, discussed and used to estimate the atmospheric lifetimes for the studied esters.