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《Atmospheric Research》2009,91(2-4):159-169
Characterizations of urban and regional sources of particulate matter (PM) were performed in the Milan area (North of Italy) during Föhn and stagnant (non-Föhn) conditions. The measurements were performed at two different places: in an urban area North of Milan (Bresso) and in a regional area at the EMEP-GAW station in Ispra (about 65 km NW from Milan) during the winter periods of the years 2002–2007. Particle size distributions and chemical bulk analysis of aerosols are combined with single particle mass spectrometry to obtain information about the chemical content of the particles and their mixing state. Föhn conditions are characterized by extremely clean background air from which background aerosol is scavenged, and consequently local sources (here defined as sources between the sampling sites and the mountain range top about 100–150 km away depending on the wind direction) determine the aerosol properties.It was observed that during Föhn events the accumulation mode in the size range 50 nm < d < 300 nm practically disappears and that the size fraction below 50 nm dominates the total number distribution. The significant change in the number size distribution and the large decrease in PM10 mass during Föhn events are accompanied by a significant change in the chemical composition of the particles. Results from bulk chemical analysis showed high amounts of carbonaceous compounds and very low concentrations of ammonium nitrate (as indicator for secondary chemistry) during Föhn episodes, in contrast to stagnant conditions, when secondary components are dominating the aerosol composition. Single particle measurements confirm the high contribution of carbonaceous compounds in locally emitted particles.It was concluded that particles that originated in the urban area come mainly from combustion processes, especially direct traffic emissions, domestic heating and industrial activities, whereas the regionally emitted particles are different with much less traffic contribution.We estimate that under prevailing (non-Föhn) winter conditions, about 50–65% of the aerosol mass load in the city of Milan are caused by local emissions, and about 35–50% come from regional background. This finding suggests that in order to improve air quality in a big city like Milan, it is important to combine local traffic restriction interventions with other long-term regional scale air-quality-measures. 相似文献
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Distribution of nitrate over sea-salt and soil derived particles — Implications from a field study 总被引：1，自引：0，他引：1
Tuomo A. Pakkanen Veli-Matti Kerminen Risto E. Hillamo Minna Màkinen Timo Màkelà Aki Virkkula 《Journal of Atmospheric Chemistry》1996,24(2):189-205
A method for determining the distribution of supermicrometer nitrate between size-segregated sea-salt and soil derived particles is presented. The analysis is based on field data from six measurements at a coastal site in southern Finland, and on a theoretical treatment taking into account the transfer of gaseous species onto particle surfaces and their subsequent reaction. Significant amounts of nitrate were found in both the particle types, with the fraction of nitrate associated with soil particles varying from 20–50% in the 1–2 m size to near 90% in particles larger than 10 m. Overall, the nitrate accumulation followed closely the relative abundances of these two particle types. Two overlapping modes in supermicron nitrate mass size distributions could be identified. The lower mode, associated with sea-salt, was located between the surface-area and volume distribution of sodium peaking at about 2–3 m of EAD. The upper mode peaked at 3–5 m and followed more closely the surface-area distribution of calcium in all samples. At our site, the accumulation of nitrate into both particle types was shown to be limited by an effective surface reaction rate rather than by gas-phase diffusion. This rate was estimated to be considerably larger for sea-salt particles. Strong evidence in support of the saturation of nitrate in sea-salt particles were obtained. 相似文献
4.
K. Slezakova J. C. M. Pires M. C. Pereira F. G. Martins M. C. Alvim-Ferraz 《Journal of Atmospheric Chemistry》2008,60(3):221-236
In urban areas traffic is the major contributor to atmospheric particulate matter and exposure to these particles currently
represents a serious risk to human health. The attention has been recently focused more on the particles of smaller sizes
(PM2.5) which penetrate deeper in respiratory system causing severe health effects. Therefore, more information on PM2.5 should be provided, namely concerning morphological and chemical characterization. Aiming further evaluation of the impact
of traffic emissions on public health, this work evaluated the influence of traffic on the chemical and morphological characteristics
of PM10 and PM2.5, collected at one site influenced by traffic emissions and at one reference site. Chemical and morphological characteristics
of 1,000 individual particles were determined by scanning electron microscopy combined with energy dispersive spectrometer
(SEM–EDS). Cluster analysis (CA) was used to identify different types of particles that occurred in PM, aiming the identification
of the respective emission sources. Traffic PM2.5 were dominated by particles composed of Fe oxides and alloys (67%) which were related to traffic emissions (this percentage
was 3.7 times higher than at the background site); in PM2.5–10 the abundance of Fe oxides and alloys were 20% and 0% for the traffic and background sites, respectively. Background PM2.5 were mainly constituted by aluminum silicates (63%) related to natural sources (this percentage was 2.5 times higher than
at the traffic site); the abundances of aluminum silicates in PM2.5–10 were 74% and 73% for traffic and background sites, respectively. It was concluded that traffic emissions were mainly present
in PM2.5 (the percentage of particles associated to these emissions was 3.4 times higher than in PM2.5–10), while coarse particles were dominated by material of natural origin (the percentage of particles associated was 1.2 and
3.0 times higher than in PM2.5 for traffic and background sites, respectively). Previous results obtained by proton induced X-ray emission (PIXE) were consistent
with SEM–EDS analysis that showed to be very useful to complement elemental analysis of different PM2.5 and PM2.5–10. 相似文献