Chemical profiling of PM10 from urban road dust.

Road dust resuspension is one of the main sources of particulate matter with impacts on air quality, health and climate. With the aim of characterising the thoracic fraction, a portable resuspension chamber was used to collect road dust from five main roads in Oporto and an urban tunnel in Braga, north of Portugal. The PM10 samples were analysed for: i) carbonates by acidification and quantification of the evolved CO2, ii) carbonaceous content (OC and EC) by a thermo-optical technique, iii) elemental composition by ICP-MS and ICP-AES after acid digestion, and iv) organic speciation by GC-MS. Dust loadings of 0.48±0.39mgPM10m-2 were obtained for asphalt paved roads. A much higher mean value was achieved in a cobbled pavement (50mgPM10m-2). In general, carbonates were not detected in PM10. OC and EC accounted for PM10 mass fractions up to 11% and 5%, respectively. Metal oxides accounted for 29±7.5% of the PM10 mass from the asphalt paved roads and 73% in samples from the cobbled street. Crustal and anthropogenic elements, associated with tyre and brake wear, dominated the inorganic fraction. PM10 comprised hundreds of organic constituents, including hopanoids, n-alkanes and other aliphatics, polycyclic aromatic hydrocarbons (PAH), alcohols, sterols, various types of acids, glycerol derivatives, lactones, sugars and derivatives, phenolic compounds and plasticizers. In samples from the cobbled street, these organic classes represented only 439µgg-1PM10, while for other pavements mass fractions up to 65mgg-1PM10 were obtained. Except for the cobbled street, on average, about 40% of the analysed organic fraction was composed of plasticizers. Although the risk via inhalation of PAH was found to be insignificant, the PM10 from some roads can contribute to an estimated excess of 332 to 2183 per million new cancer cases in adults exposed via ingestion and dermal contact.

Detailed chemical analysis of regional-scale air pollution in western Portugal using an adapted version of MCM v3.1.

A version of the Master Chemical Mechanism (MCM) v3.1, refined on the basis of recent chamber evaluations, has been incorporated into a Photochemical Trajectory Model (PTM) and applied to the simulation of boundary layer photochemistry in the Portuguese west coast region. Comparison of modelled concentrations of ozone and a number of other species (NO(x) and selected hydrocarbons and organic oxygenates) was carried out, using data from three connected sites on two case study days when well-defined sea breeze conditions were established. The ozone concentrations obtained through the application of the PTM are a good approximation to the measured values, the average difference being ca. 15%, indicating that the model was acceptable for evaluation of the details of the chemical processing. The detailed chemistry is examined, allowing conclusions to be drawn concerning chemical interferences in the measurements of NO(2), and in relation to the sensitivity of ozone formation to changes in ambient temperature. Three important, and comparable, contributions to the temperature sensitivity are identified and quantified, namely (i) an effect of increasing biogenic emissions with temperature; (ii) an effect of increasing ambient water vapour concentration with temperature, and its influence on radical production; and (iii) an increase in VOC oxidation chain lengths resulting from the temperature-dependence of the kinetic parameters, particularly in relation to the stability of PAN and its higher analogues. The sensitivity of the simulations to the refinements implemented into MCM v3.1 are also presented and discussed.

Volatile organic compounds in rural atmospheres of central Portugal.

Atmospheric concentrations of volatile organic compounds were measured at two rural sites in central Portugal. The sites were chosen to be in line with the summer northwesterly sea breezes in order to study the evolution of the chemical composition of air masses during transport to inland areas. The most abundant non-oxygenated hydrocarbon in the ambient air was isoprene and the monoterpenes alpha-pinene, beta-pinene and 1,8 cineol. The maximum isoprene levels (6-7 ppb) were recorded at the most inland site, suggesting an enrichment of coastal air masses with biogenic emissions during transport over eucalyptus forests. Formaldehyde was the most prominent carbonyl compound in the atmosphere but acetaldehyde and acrolein were also abundant. Concentrations of carbonyl compounds had a tendency to be higher inland, particularly for glyoxal, methyl glyoxal, methyl vinyl ketone, metacrolein and pentanal. The observed increases indicate that carbonyls were produced by photochemical oxidation of biogenic hydrocarbons in aged air masses with coastal origin. Isoprene, monoterpenes and various carbonyls exhibited pronounced diurnal variations, which are explained on the basis of emissions from vegetation, oxidation pathways of biogenic hydrocarbons and meteorological conditions.

Assessment of air pollution sources in an industrial atmosphere using principal component and multilinear regression analysis.

Aerosol samples collected in the industrial area of Estarreja, Portugal, were used to assess the source classes responsible for the particulate levels observed in the local atmosphere. Principal Component Analysis was applied separately to the concentrations of aerosol constituents and meteorological variables to obtain the number of Principal Components and to verify the influence of weather conditions on ambient air quality. The technique led to the conclusion that soil and transport emissions represent important aerosol sources even in this industrial environment. The quantitative contribution of each source class was calculated using Multilinear Regression Analysis; 37% of the aerosol mass had a soil origin, 8% was from sea spray, 18% resulted from transport emissions and 24% contained ammonium salts. Twelve percent of total suspended particle (TSP) mass could not be explained by any of the six Principal Components retained. Ammonium salts and two other minor Principal Components seem to result mainly from industrial emissions. More specific information about the contribution of each particular source was not possible with this technique.