R. Guillermo

An investigation into the traffic-related fraction of isoprene at an urban location

Abstract Continuous hourly measurements of isoprene and 30 other hydrocarbons were performed at an urban centre site in Lille, France, from May 1997 to April 1999. Parallel mass emissions of the same hydrocarbons from in-service passenger vehicles were determined from measurements made on a chassis dynamometer using the European MVEG driving cycle. On the one hand, descriptive statistics and principal component analysis revealed the strong traffic origin of isoprene in winter months and its double biogenic and anthropogenic origin during the summer. On the other hand, the emission measurements of individual hydrocarbons in exhaust gases confirmed the presence of isoprene in petrol fuelled (with or without catalytic converters) and diesel car exhausts. Finally, the isoprene/acetylene ratios, both of them derived from ambient concentrations and emission factors, were compared. No statistically significant difference was found in winter, indicating the strict traffic origin of isoprene during that period. For the winter period, a simple regression analysis was performed on daily isoprene concentrations vs. those of acetylene and three other exhaust gases tracers—propene, ethylene and 1,3-butadiene. The established regression equations, together with the four tracer concentrations, were used to estimate the vehicle exhaust fractions of isoprene. From November to March, vehicle exhaust explained the totality of isoprene levels. While traffic remained the major source of isoprene with a contribution greater than 50% during the growing season, it still constituted a non-negligible source of isoprene in summer, anti-correlated to temperature and fluctuating between 10% and 50%. The application with 1,3-butadiene gives the greatest estimation of the anthropogenic fraction of isoprene. Other sources of 1,3-butadiene, acetylene, ethylene and propene were suspected in addition to their known traffic origin.

Characterisation of NMHCs in a French urban atmosphere: overview of the main sources.

Continuous hourly air quality data involving 37 C2-C9 non-methane hydrocarbons (NMHC) over 4 years are reported for the first time in Lille metropol, northern France, at two urban roadside and background sites. The data have been analysed in two complementary steps: univariate statistics which define the spatial and temporal characteristics of NMHC by constructing the seasonal and daily concentration profiles, and multivariate statistics based on principal component analysis (PCA). A number of important sources have been clearly identified depending on the season: (1) motor vehicle exhaust, which dominates the NMHC distribution and particularly in winter, even for isoprene; (2) wintertime stationary combustion and activities related to fossil fuel consumption in general, such as natural gas leakage of ethane and propane; (3) summertime evaporative emissions from fuel and solvent; and (4) summertime biogenic emissions through isoprene behaviour and their dependence on temperature.

Source identification and variation in the chemical composition of precipitation at two rural sites in France

A receptor-oriented model is developed to identify and locate the sources of the constituents present in precipitation collected at two rural French stations, namely Donon and Morvan. Firstly, factor analysis is applied to the chemical data sets. Three factors are identified reproducing the concentrations observed in precipitation. These factors represent the acid sources (characterized by the ionic combination between H+, SO42− and NO3−), marine sources (Na+, Cl− and Mg2+) and crustal sources (Ca2+ and K+). Then, the factor scores of samples are combined with the air parcel back trajectories in the same scheme of model calculation to produce the probability maps of source locations. This approach, called potential source contribution function (PSCF) analysis, locates the acid sources in the industrial areas of Northeastern Europe and Great Britain, the marine sources in the Atlantic Ocean and the crustal sources around the Mediterranean Basin. The seasonal profiles of these factors are performed and contrasted with the atmospheric processes and meteorological conditions which prevail in each season. A classification of these daily samples is also made according to four origin sectors, to examine the variations in ionic composition of precipitations from one sector to another. The results of this classification are in agreement with the source locations found by the PSCF analysis.

A study of the source-receptor relationships influencing the acidity of precipitation collected at a rural site in France

In order to examine the qualitative and quantitative source–receptor relationships responsible for acid rains at a background site in France, a receptor-oriented model was applied to the precipitation data collected from 1992 to 1995. Origins of acidic and alkaline species in precipitations have been investigated. The methodology combines precipitation chemical data with air parcel backward trajectories to establish concentration field maps of likely contributing sources. Highest acidities and concentrations of sulfate and nitrate in precipitation were associated with transport from the high emission areas of central Europe. Alkaline events were associated with air masses originating from Mediterranean basin or northern Africa. The quantitative relationships between the maps of potential sources and the European emissions of SO2 and NOx were examined performing a correlation analysis. Good correlations were found between computed concentrations of acidic species and emissions of SO2 and NOx. Substantial seasonal variations of acidic species were revealed. The highest concentrations occurred during the warm season. These seasonal variations are the effect of change of meteorological conditions and of the strength atmospheric processes according to the season.

Performances and application of a passive sampling method for the simultaneous determination of nitrogen dioxide and sulfur dioxide in ambient air.

The performances and applicability of a diffusion tubesampler for the simultaneous measurements of NO2 andSO2 in ambient air were evaluated. SO2 andNO2are collected by the passive sampler using triethanolamine astrapping agent and are determined as sulphate and nitrite withion chromatography. The detection limit (2.3 μg m-3 ofNO2 and 4.2 μg m-3 of SO2 for two weekssampling) is adequate for the determination of concentrationsin urban and industrial areas. Precision of the method as RSDis in mean 5% for NO2 and 12% for SO2 at theconcentration levels in urban areas. Calibration of the methodwas performed in the field conditions by comparison between theresponses of sampler and the concentrations measured by thecontinuous monitors. High degree of linearity (correlationcoefficients > 0.8) is found between the passive sampler tubeand the continuous monitor data for both NO2 and SO2.To reduce the wind velocity influence on passive sampling ofdiffusion tubes, a protective shelter was tested in this study.The overall uncertainty of one measure for the optimised methodis estimated at 5 μg m-3 for NO2 and 6μg m-3 for SO2. Suitability of this passivesampling method for air pollution monitoring in urban areas wasdemonstrated by the results shown in this paper on a campaigncarried out in the French agglomeration.

Metal Speciation in Soil: Extraction of Exchangeable Cations from a Calcareous Soil with a Magnesium Nitrate Solution

Abstract The exchangeable fraction of metals in a calcareous soil was studied with a magnesium nitrate solution and its extraction procedure was optimised. Parameters like extraction time, pH and concentration of the extractant solution, number of extractions or soil/solution ratio were examined. Experiments showed that after a 1-hour extraction, an equilibrium was established between extracted and re-sorbed metal. Moreover, carrying-out successive extractions re-sorbed quantities and maximum extracted ones could be estimated. Initial pH was fixed at 7 to avoid carbonates dissolution or hydroxides precipitation. A concentration of 0.5 mol/L and a soil/solution ratio of 1/20 were chosen. Leachate analyses showed a good selectivity of the extraction toward other soil fractions.

A Qualitative Determination of the Source Locations of Precipitation Constituents in Morvan, France

A statistical receptor-oriented model is developed to examine the long-range transport of precipitation constituents to the background station at Morvan (elevation 620 m, latitude 47°16′ N and longitude 04°05′ E), France. This model computes a probability function called PSCF (Potential Source Contribution Function) which is based on the air parcel trajectory data coupled with precipitation chemical data associated to that air parcel. The PSCF value is the ratio of the probability of a contamined air parcel having traversed a 2° latitude by 2° longitude area to the probability that any air parcel traversed that area. Regions with high PSCF values thus have a higher probability of contributing pollutants to the measured depositions at the receptor site. This approach suggests that the sources of the major acid forms (H2SO4 and HNO3) are located in the east of Germany and the middle of Great Britain, the Ca2+ sources in the Mediterranean basin and the Na+, Cl− and Mg2+ sources in the Atlantic Ocean.

Gas-phase reaction of n-butyl acetate with the hydroxyl radical under simulated tropospheric conditions: Relative rate constant and product study

The gas-phase reaction of n-butyl acetate with hydroxyl radicals has been studied in an environmental smog chamber at 298 K atmospheric pressure, and simulated tropospheric concentrations. The rate constant for this reaction has been determined by a relative method and the experimental result, relative to n-octane used as reference compound, is This value appears to be about 25% higher than absolute rate constants found in the literature, but agrees very well with the other relative determination. Two reaction products have been identified and their production yield has been estimated, each accounting for about (15 ± 5)% of the overall OH reaction processes. The two observed products are \centerline{ 2--oxobutil acetate (

Intercomparison between three receptor-oriented models applied to acidic species in precipitation

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Spatial variability and source identification of rural precipitation chemistry in France

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