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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.

SSCI-VIDE+CARE+JSH:MPI:YDU:RCI:LTI:SRS:CGO; International audience; Organosulfates are tracers for secondary organic aerosol (SOA) formation. We propose a new mechanism of organosulfur product formationin the atmosphere, in which sulfur dioxide (SO2) reacts directly withalkenes. The experiments were conducted at the gas-liquid interface witha coated-wall flow tube reactor. It was shown, for the first time, thatSO2 reacts efficiently with the unsaturated bond in oleic acid underatmospheric conditions (without ozone), leading to the formation of C-9and C-18 organosulfur products. The associated uptake coefficients werein excess of 10(-6), decreasing with initial SO2 concentration andincreasing with humidity. These results might explain a fraction oforganosulfur products detected in atmospheric particles. This work tendsto elucidate the role of organosulfates' interfacial chemistry as apotentially unrecognized pathway for their contribution to SOAformation; however, it remains to be determined how significant thispathway is to the overall organosulfate abundances measured in ambientaerosol.

SSCI-VIDE+CARE+RCI:FBE:ABO:NCA:YDU:CGO; International audience; During the European Life+ project PhotoPAQ (Demonstration of Photocatalytic remediation Processes on Air Quality), photocatalytic remediation of nitrogen oxides (NOx), ozone (O3), volatile organic compounds (VOCs), and airborne particles on photocatalytic cementitious coating materials was studied in an artificial street canyon setup by comparing with a colocated nonactive reference canyon of the same dimension (5 × 5 × 53 m). Although the photocatalytic material showed reasonably high activity in laboratory studies, no significant reduction of NOx, O3, and VOCs and no impact on particle mass, size distribution, and chemical composition were observed in the field campaign. When comparing nighttime and daytime correlation plots of the two canyons, an average upper limit NOx remediation of ≤2 % was derived. This result is consistent only with three recent field studies on photocatalytic NOx remediation in the urban atmosphere, whereas much higher reductions were obtained in most other field investigations. Reasons for the controversial results are discussed, and a more consistent picture of the quantitative remediation is obtained after extrapolation of the results from the various field campaigns to realistic main urban street canyon conditions.

SSCI-VIDE+CARE+HFU:RCI:YDU:MPI:LTI:SRS:SPR:CGO; International audience; We report on experiments that probe photosensitized chemistry at the air/water interface, a region that does not just connect the two phases but displays its own specific chemistry. Here, we follow reactions of octanol, a proxy for environmentally relevant soluble surfactants, initiated by an attack by triplet-state carbonyl compounds, which are themselves concentrated at the interface by the presence of this surfactant. Gas-phase products are determined using PTR-ToF-MS, and those remaining in the organic layer are determined by ATR-FTIR spectroscopy and HPLC-HRMS. We observe the photosensitized production of carboxylic acids as well as unsaturated and branched-chain oxygenated products, compounds that act as organic aerosol precursors and had been thought to be produced solely by biological activity. A mechanism that is consistent with the observations is detailed here, and the energetics of several key reactions are calculated using quantum chemical methods. The results suggest that the concentrating nature of the interface leads to its being a favorable venue for radical reactions yielding complex and functionalized products that themselves could initiate further secondary chemistry and new particle formation in the atmospheric environment.

SSCI-VIDE+CARE:+ABO:YDU:CGO; International audience; During the European Life+ project PhotoPAQ (Demonstration of Photocatalytic remediation Processes on Air Quality), photocatalytic remediation of nitrogen oxides (NOx) was studied in the Leopold II tunnel in Brussels, Belgium, using photocatalytic cementitious coating materials and an artificial UV lighting system. Three different approaches were used to quantify the pollution reduction, i.e. measurements before/after application, upwind/downwind of the test section and with UV lamps on/off. In contrast to first estimations based on laboratory studies on fresh samples, the field results showed no observable reduction of NOx in the tunnel. An upper limit of 2% was determined for the maximum possible NOx reduction, which corresponds to the experimental uncertainties. Serious passivation of the surface reactivity under the heavily polluted tunnel conditions by one order of magnitude was identified in laboratory experiments subsequent to the tunnel study as the main reason for the observed low remediation. In addition, high relative humidity and wind speed inside the tunnel further limited the photocatalytic uptake of NOx. When using the uptake kinetics from the laboratory experiments on passivized tunnel samples, simple model calculations based on a first order reaction kinetics indicate only an upper limit photocatalytic remediation inside the 160 m tunnel section of 0.4%, which is clearly below the experimental uncertainties and thus, in excellent agreement with the tunnel results. Optimized experimental conditions, for which this technology might be applicable in road tunnels, are discussed. (C) 2014 Elsevier Ltd. All rights reserved.

AIR+DRE:YDU:CGO; Understanding new particles formation in the free troposphere is key for air quality and climate change, but requires accurate observation tools. Here, we discuss on the optical requirements ensuring a backscattering device, such as a lidar, to remotely observe nucleation events promoted by nonspherical desert dust or volcanic ash particles. By applying the Mie theory and the T-matrix code, we numerically simulated the backscattering coefficient of spherical freshly nucleated particles and nonspherical particles. We hence showed that, to remotely observe such nucleation events with an elastic lidar device, it should operate in the UV spectral range and be polarization-resolved. Two atmospheric case studies are proposed, on nucleation events promoted by desert dust, or volcanic ash particles. This optical pathway might be useful for climate, geophysical and fundamental purposes, by providing a range-resolved remote observation of nucleation events. (C)2014 Optical Society of America

Large quantities of mineral dust particles are frequently ejected into the atmosphere through the action of wind. The surface of dust particles acts as a sink for many gases, such as sulfur dioxide. It is well known that under most conditions, sulfur dioxide reacts on dust particle surfaces, leading to the production of sulfate ions. In this report, for specific atmospheric conditions, we provide evidence for an alternate pathway in which a series of reactions under solar UV light produces first gaseous sulfuric acid as an intermediate product before surface-bound sulfate. Metal oxides present in mineral dust act as atmospheric photocatalysts promoting the formation of gaseous OH radicals, which initiate the conversion of SO 2 to H 2 SO 4 in the vicinity of dust particles. Under low dust conditions, this process may lead to nucleation events in the atmosphere. The laboratory findings are supported by recent field observations near Beijing, China, and Lyon, France.