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| Titel |
How much is particulate matter near the ground influenced by upper-level processes within and above the PBL? A summertime case study in Milan (Italy) evidences the distinctive role of nitrate |
| VerfasserIn |
G. Curci, L. Ferrero, P. Tuccella, F. Barnaba, F. Angelini, E. Bolzacchini, C. Carbone, H. A. C. Denier van der Gon, M. C. Facchini, G. P. Gobbi, J. P. P. Kuenen, T. C. Landi, C. Perrino, M. G. Perrone, G. Sangiorgi, P. Stocchi |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1680-7316
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| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 15, no. 5 ; Nr. 15, no. 5 (2015-03-09), S.2629-2649 |
| Datensatznummer |
250119506
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| Publikation (Nr.) |
 copernicus.org/acp-15-2629-2015.pdf |
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| Zusammenfassung |
| Chemical and dynamical processes lead to the formation of aerosol layers in
the upper planetary boundary layer (PBL) and above it. Through vertical
mixing and entrainment into the PBL these layers may contribute to the
ground-level particulate matter (PM); however, to date a quantitative
assessment of such a contribution has not been carried out. This study
investigates this aspect by combining chemical and physical aerosol
measurements with WRF/Chem (Weather Research and Forecasting with
Chemistry) model simulations. The observations were
collected in the Milan urban area (northern Italy) during the summer of 2007.
The period coincided with the passage of a meteorological perturbation that
cleansed the lower atmosphere, followed by a high-pressure period favouring
pollutant accumulation. Lidar observations revealed the formation of
elevated aerosol layers and evidence of their entrainment into the PBL. We
analysed the budget of ground-level PM2.5 (particulate matter with an
aerodynamic diameter less than 2.5 μm) with the help of the online
meteorology–chemistry WRF/Chem model, focusing in particular on the
contribution of upper-level processes. Our findings show that an important
player in determining the upper-PBL aerosol layer is particulate nitrate,
which may reach higher values in the upper PBL (up to 30% of the aerosol
mass) than in the lower PBL. The nitrate formation process is predicted to
be largely driven by the relative-humidity vertical profile, which may
trigger efficient aqueous nitrate formation when exceeding the ammonium
nitrate deliquescence point. Secondary PM2.5 produced in the upper half
of the PBL may contribute up to 7–8 μg m−3 (or 25%) to ground-level concentrations on an hourly basis. The residual aerosol layer above the PBL is also found to potentially play a large role, which may
occasionally contribute up to 10–12 μg m−3 (or 40%) to hourly
ground-level PM2.5 concentrations during the morning hours. Although
the results presented here refer to one relatively short period in one
location, this study highlights the importance of considering the interplay
between chemical and dynamical processes occurring within and above the PBL
when interpreting ground-level aerosol observations. |
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