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|Title:||Sources for PM air pollution in the Po Plain, Italy: II. Probabilistic uncertainty characterization and sensitivity analysis of secondary and primary sources|
|Authors:||LARSEN Bo; GILARDONI Stefania; STENSTRÖM Kristina; NIEDZIALEK Joanna; JIMENEZ Jose; BELIS CLAUDIO|
|Citation:||ATMOSPHERIC ENVIRONMENT vol. 50 p. 203-213|
|Publisher:||PERGAMON-ELSEVIER SCIENCE LTD|
|Type:||Articles in periodicals and books|
|Abstract:||Very high levels of ambient particulate matter (PM) are frequently encountered in the north of Italy and air quality limits are regularly exceeded. To obtain quantitative information on the pollution sources and to gain understanding of the dynamics of pollution episodes in this populated area PM10 and PM2.5 samples were collected daily at nine urban to regional sites distributed over the central Po Plain and one site in the Valtelline Valley. In total 23 five-week winter campaigns and one summer/autumn campaign (2007-2009) were organized. The PM was analyzed for 61 chemical constituents and a data-base was built up consisting of approx. 70000 records of the concentrations and their associated uncertainty. In addition 14C/12C ratios were determined in PM10 from four sites. Primary and secondary sources were quantified using macro-tracer methods, chemical mass balance modelling, and positive matrix factorization and the combined results were evaluated by probability- and sensitivity analysis. Monte Carlo simulations yielded probability distributions for seven source categories contributing to the carbonaceous fraction of PM and five source categories contributing to the PM10 and PM2.5 mass. In general, lower uncertainties were evident for the source contribution estimates for the PM mass than for the carbonaceous fractions. Secondary aerosol formed simultaneously over the Po Plain was demonstrated to be the main responsible for the typical, rapid build-up of air pollution after clean-air episodes. In the Po Plain during winter, the main source for PM is secondary aerosol with median contributions of 36% (SIA) and 18% (SOA) to the PM10 mass (2007) and 49% (SIA) and 26% (SOA) of the PM2.5 mass (2009). The absolute SCEs for the site categories (medians) varied from 20 to 38 µg/m3 for SIA and from 12 to 16 µg/m3 for SOA. The second most important source is primary emissions from road transport (traffic), comprising engine exhaust, brake/tire wear, and re-suspended road dust. The median traffic contribution for all Po Plain stations was 17 % of the PM10 mass (2007), and 16 % of the PM2.5 mass (2009). The absolute SCEs for the site categories (medians) varied from 4 µg/m3 at the regional background sites to 25 µg/m-3 at the kerb-side station and for this source similar SCEs were revealed for winter and summer/autumn. BB is the third most important source during winter with median contributions for all Po Plain stations of stations of 10% to the PM10 mass (2007) and 12% to the PM2.5 mass (2009). The absolute SCEs for the site categories (medians) varied from 5 to 12 µg/m3 and were highest at the residential area. This fact, together with the much lower SCEs measured during a summer/autumn campaign support the assumption that BB derives mainly from residential heating. In the Valtelline Valley higher median contributions from BB were revealed (15 µg/m3 corresponding to 31% of the mass) and lower median contributions from secondary sources (14-15 µg/m3 corresponding to 29-30% of the mass) and soil re-suspension (2-4 µg/m3 corresponding to 4-8% of the mass) Other sources identified in this study were minor and local, such as soil re-suspension, cement production, residential heating by fuel oil combustion, and road salting.|
|JRC Institute:||Institute for Environment and Sustainability|
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