Effects of traffic-related nitrogenous emissions on purple moor grass (Molinia caerulea (L.) Moench) transplants, used here as a new biomonitoring species, were assessed along 500 m long transects orthogonal to roads located in two open areas in the Maurienne valley (French Alps). Leaves were sampled during summer 2004 and 2005 for total N-content and 15N-abundance determination while nitrogen oxides (NO and NO2) concentrations were determined using passive diffusion samplers. A significant and negative correlation was observed between plant total N-content, and 15N-abundance and the logarithm of the distance to the road axis. The strongest decreases in plant N parameters were observed between 15 and 100 m from road axis. They were equivalent to background levels at a distance of about 800 m from the roads. In addition, motor vehicle pollution significantly affected vegetation at road edge, as was established from the relationship between leaf 15N-abundance, total N-content and road traffic densities.

Assessing air quality in street canyons is a crucial concern, as the highest pollution levels and threshold exceedances are usually experienced within this kind of urban streets. A brief overview based on experimental studies and modelling techniques undertaken in literature is presented, including characteristic features affecting wind flow and pollutant dispersion within street canyons. In this work, a numerical street canyon model intercomparison has been performed in a typical urban canyon in Florence, Italy. In particular, STREET, Canyon Plume Box Model (CPBM) and Operational Street Pollution Model (OSPM) have been applied to compute the street-level 1-h carbon monoxide (CO) concentrations. In addition, the CALINE4 model has been applied to test the site morphology. Input data cover a 1-year time period and include meteorological observations as well as measured traffic volumes and driving speeds. Hourly road emissions have been calculated using the COPERT methodology taking into account vehicle fleet, traffic flows and driving speed, as well as ambient temperature to account for cold overemissions. A preliminary experimental data analysis has been carried out in order to investigate the dependence of observed CO concentrations on meteorological and traffic parameters. Hourly CO concentrations observed over the full year have been used to compare the STREET, CPB and OSP models, resulting in a detailed statistical analysis carried out by wind sector as well as on a seasonal basis.

The city of La Plata and its surroundings are a very populated area, which has an important Industrial Pole and intense traffic activity but environmental studies have been rare so far. This article presents and discusses the importance of wind frequencies and velocities for the transport of air pollutants. The study emphasizes the importance of knowing wind patterns on an hourly basis that can be helpful for designing a monitoring network as well as for preventing exposure to pollutants. Correlation between monthly SO₂ concentrations and wind frequencies and velocities are discussed for a particular set of directions NNW-NE that carry pollutants from industrial sources toward populated areas. As a result, averaged wind frequencies have been found to be very important for determining patterns influencing pollutants transport; the influence of averaged velocities has shown low variability (hourly and monthly). Hierarchical cluster analysis applied to wind roses provided a useful approach for analyzing and describing the general daily occurrence of winds.

Background, aim and scope Salt efflorescences markedly contribute to the alteration and deterioration of building material, in this case the Villamayor Sandstone of the facades in the Old Town of Salamanca, Spain (United Nations Educational, Scientific and Cultural Organization world cultural heritage site). A better understanding of the mechanisms of salt formation and the involved elements would allow more precise measures in monument conservation. The magnesium which is required for the salt precipitation originates from selective processes of hydrolysis. The source of sulphate, however, is presently not as clear. Identifying the source of the sulphur was the main goal of this research. Isotope ratio measurement of δ³⁴S and δ¹⁸O was used to clarify the origins of Mg sulphate salts. Materials and methods A total of 56 Mg sulphate samples were collected in two different seasons (July and November 2005) from monuments of the Old Town of Salamanca. These sampled salt efflorescences were analysed for δ³⁴S and δ¹⁸O by mass spectrometry. A ‘dual-inlet' type by VG Isotech was used for δ³⁴S and continuous flow type Isoprime by GV Instruments for δ¹⁸O. Samples were measured in triplicates and standard material was analysed for quality control. Results δ³⁴S values range between 3.6‰ and 15.4‰ with a median value of 10.2‰ for the July samples and of 10.1‰ for November samples. The results of the sulphur ratios hint towards a bimodal distribution (with modes at δ³⁴S = 6‰ and 12‰) for winter samples, which is less obvious during summer. δ¹⁸O values range from 7.1‰ to 41.1‰. However, most values range from 7.1‰ to 20.8‰, whereas only few summer samples show outliers towards higher δ¹⁸O values. The median δ¹⁸O value for July samples is 15.5‰ and for November samples 14.6‰. Discussion The isotopic ratios of the analysed sulphate samples were compared with values of possible source materials. Sulphur sources in the case of Salamanca are barites from the Villamayor Sandstone itself, sea spray, sulphides from regional rocks, biogenic sulphur (soil, avian excreta), as well as sulphur from anthropogenic sources such as building materials (especially mortar) or traffic exhaust. Salamanca is a representative site for non-industrial cities with no heavy industry and thus, there are no significant SO₂ emissions from industry. Conclusions Based on the measured isotopic ratios, it was ascertained that more than one sole sulphur source is present. However, based on additional information about the source material and possible transport ways, some sources could be excluded whereas others only played a minor role. Finally, there is strong indication that the main sulphur source is atmospheric pollution and the exhaust emissions from vehicles in particular, while mortar as building material also contributes to a minor extent. The δ¹⁸O values support this hypothesis. Moreover, the reported δ¹⁸O values are a strong indicator of the secondary nature of the Mg sulphates. Isotope ratio measurement and especially the combined use of δ³⁴S and δ¹⁸O values have proven to be a good instrument in clarifying the origin of salt efflorescences on buildings. Recommendations and perspectives Further studies should investigate more closely the isotopic composition of atmospheric aerosols in Salamanca in order to get a more detailed knowledge about the main sulphur sources, as well as to quantify the relation between the isotopic values and the amount and mineralogical form of the salts.