 |
| Titel |
Changes in particulate matter physical properties during Saharan advections over Rome (Italy): a four-year study, 2001–2004 |
| VerfasserIn |
G. P. Gobbi, F. Angelini, F. Barnaba, F. Costabile, J. M. Baldasano, S. Basart, R. Sozzi, A. Bolignano |
| Medientyp |
Artikel
|
| Sprache |
Englisch
|
| ISSN |
1680-7316
|
| Digitales Dokument |
URL |
| Erschienen |
In: Atmospheric Chemistry and Physics ; 13, no. 15 ; Nr. 13, no. 15 (2013-08-01), S.7395-7404 |
| Datensatznummer |
250018799
|
| Publikation (Nr.) |
 copernicus.org/acp-13-7395-2013.pdf |
|
|
|
|
|
| Zusammenfassung |
Particulate matter mass concentrations measured in the city of Rome (Italy)
in the period 2001–2004 have been cross-analysed with concurrent Saharan
dust advection events to infer the impact these natural episodes bear on the
standard air quality parameter PM10 observed at two city stations and
at one regional background station. Natural events such as Saharan dust
advections are associated with a definite health risk. At the same time, the
Directive 2008/50/EC allows subtraction of PM exceedances caused by natural
contributions from statistics used to determine air quality of EU sites. In
this respect, it is important to detect and characterise such advections by
means of reliable, operational techniques. To assess the PM10 increase
we used both the "regional-background method" suggested by EC Guidelines
and a "local background" method, demonstrated to be most suited to this
central Mediterranean region. In terms of exceedances, the two approaches
provided results within ~20% of each other at background
sites, and at ~50% of each other in traffic conditions.
The sequence of Saharan advections over the city has been either detected by
Polarization Lidar (laser radar) observations or forecast by the operational
numerical regional mineral dust model BSC-DREAM8b of the Barcelona
Supercomputing Centre. Lidar observations were also employed to retrieve the
average physical properties of the dust clouds as a function of height. Over
the four-year period, Lidar measurements (703 evenly distributed days)
revealed Saharan plumes transits over Rome on 28.6% of the days, with
minimum occurrence in wintertime. Dust was observed to reach the ground on
17.5% of the days totalling 88 episodes. Most (90%) of these
advections lasted up to 5 days, averaging to ~3 days. Median
time lag between advections was 7 days. Typical altitude range of the dust
plumes was 0–6 km, with the centre of mass at ~3 km a.g.l.
BSC-DREAM8b model simulations (1461 days) predicted Lidar detectable (532 nm
extinction coefficient > 0.005 km−1) dust advections on
25.9% of the days, with ground contacts on 13% of the days. As in the
Lidar case, the average dust centre of mass was forecast at ~3 km. Along
the 703 day Lidar dataset, model forecast and Lidar detection of
the presence of dust coincided on 80% of the cases, 92% coincidences
are found within a ±1 day window.
Combination of the BSC-DREAM8b and Lidar records leads to about 21% of
the days being affected by presence of Saharan dust at the ground. This
combined dataset has been used to compute the increase in PM with respect to
dust-unaffected previous days. This analysis has shown Saharan dust events
to exert a meaningful impact on the PM10 records, causing average
increases of the order of 11.9 μg m−3. Conversely, PM10
increases computed relying only on the Lidar detections (i.e., presence of
dust layers actually observed) were of the order of 15.6 μg m−3.
Both analyses indicate the annual average contribution of dust advections to
the city PM10 mass concentrations to be of the order of 2.35 μg m−3.
The number of exceedances attributable to Saharan advections at
the three station types addressed in this study (urban traffic, urban
background and regional background) were found to be 25%, 30% and
43%, respectively. These results confirm Saharan advections in the
central Mediterranean as important modulators of PM10 loads and
exceedances. |
| |
|
| Teil von |
|
|
|
|
|
|
|
|