Fog occurrence and chemical composition in the Po valley over the last twenty years
Introduction
During the fall–winter season, fog is a very frequent phenomenon in the Po Valley (northern Italy) (Fuzzi et al., 1996). Beside the well-known detrimental effects of the reduced visibility on the transportation system, the interaction between fog droplets and atmospheric pollutants may have also an important impact on the local environment, agriculture and human health (Balmes et al., 1989, Butler and Trumble, 2008, Dollard et al., 1983, Fenn et al., 2007, Shigihara et al., 2009, Waldman et al., 1985). The Po Valley area is characterised by the highest population density in Italy, approximately 30% of the Italian population lives there, and by intensive industrial, agricultural and trading activities. Consequently, a high load of pollutants is emitted into the atmosphere. Furthermore the orography of the area, which is surrounded by the Alpine chain to the north and west sides and by the Apennines to the south, frequently favours stagnation of the pollutants in the air. In the fall–winter months, high pressure and clear sky conditions, together with a sufficient amount of humidity in the air, provide the favourable conditions for the formation of radiation fogs. The interaction of aerosols and gases with fog droplets can affect the chemical composition as well as the lifetime of atmospheric pollutants (Collett et al., 2008, Dall'Osto et al., 2009, Gilardoni et al., 2014, Kaul et al., 2011, Wang et al., 2012, Yang et al., 2012).
At the beginning of the 1980's, the first fog samples were collected at the field station of San Pietro Capofiume (Fuzzi et al., 1983), which is located in an agricultural area in the south-eastern part of the Po Valley, 30 km north-east of Bologna (Fig. 1).
Initially fog droplets were sampled occasionally on a field campaign basis. Starting from November 1989, a regular program of fog sampling has been implemented every year in the fall–winter season (November–March), in conditions of dense fog occurrence (Fuzzi et al., 1996, Fuzzi et al., 1992, Fuzzi et al., 1997). This systematic activity, which is still on-going, enabled us to build an over twenty years long database of fog water chemical composition, pH, conductivity and liquid water content (LWC). This database represents a valuable tool to test the effectiveness of the implemented air quality policies, and can also be used to support future policy actions in the region. The spatial variability of fog chemistry over the whole Po Valley has also been investigated during shorter-term experiments (Fuzzi et al., 1996). These studies indicate a relatively homogeneous fog chemical composition across the valley. Based on such observations, the trends presented in this paper can reasonably be considered representative for the whole Po Valley basin.
This paper summarizes fog measurements results collected over twenty years in San Pietro Capofiume, discusses temporal trends in fog chemical composition, and reviews results of short term studies on specific fog chemical components.
Section snippets
Fog water collection
At the field station of San Pietro Capofiume, monitoring of fog occurrence and fog water collection have been performed from November to March systematically since 1989. At this station, several experiments had already been carried out earlier during the 1980's (Fuzzi et al., 1983, Fuzzi et al., 1988, Fuzzi et al., 1985, Winiwarter et al., 1988), but they were set up within intensive field campaigns and the available results cannot be considered representative for the whole season.
Fog water is
Fog frequency
A decrease of the frequency and persistence of fog throughout Europe over the last decades was described by Vautard et al. (2009). These authors report that the frequency of low-visibility conditions such as fog, mist and haze has declined in Europe over the past 30 years, for all seasons and all visibility ranges between distances of 0 and 8 km. This decline is spatially and temporally correlated with trends in sulphur dioxide emissions, suggesting a significant contribution of air-quality
Conclusions
A more than twenty year long database of fog chemical composition, pH, conductivity, LWC and frequency of dense fog events (visibility < 200 m) has been assembled, based on measurements carried out at the field station of San Pietro Capofiume in the eastern part of the Po Valley, Italy.
A reduction in fog occurrence over the last thirty years has been registered at the Bologna airport, in agreement with what has been observed in the rest of Europe. Anyway, we can not establish the reason of the
Acknowledgements
Giordano Orsi designed the entire fog water collection program and followed its functioning over the years. The Authors acknowledge the contribution of Valeriana Mancinelli in the elaboration of the database used for the preparation of this paper. The access to visibility data was kindly provided by Dr. Sandro Nanni (ARPA Emilia Romagna, Servizio Idro-Meteo-Clima of Bologna). Jean-Philippe Putaud is gratefully acknowledged for the carbon analysis performed on quartz filters.
References (47)
- et al.
Probabilistic relationship between liquid water content and ion concentrations in cloud water
Atmos. Res.
(2010) - et al.
Effects of pollutants on bottom-up and top-down processes in insect-plant interactions
Environ. Pollut.
(2008) - et al.
Processing of atmospheric organic matter by California radiation fogs
Atmos. Res.
(2008) - et al.
Chemical features and seasonal variation of fine aerosol water-soluble organic compounds in the Po Valley, Italy
Atmos. Environ.
(2001) - et al.
Control of solute concentrations in cloud and fog water by liquid water content
Atmos. Environ.
(2000) - et al.
Reply to discussion on “control of solute concentrations in cloud and fog water by liquid water content”
Atmos. Environ.
(2002) - et al.
Atmospheric deposition inputs and effects on lichen chemistry and indicator species in the Columbia River Gorge, USA
Environ. Pollut.
(2007) - et al.
Soluble organic compounds in fog and cloud droplets: what have we learned over the past few years?
Atmos. Res.
(2002) - et al.
The NEVALPA project: a regional network for fog chemical climatology over the Po Valley basin
Atmos. Environ.
(1996) - et al.
Radiation fog liquid water acidity at a field station in the Po Valley
J. Aerosol Sci.
(1983)
A review of observations of organic matter in fogs and clouds: origin, processing and fate
Atmos. Res.
Linear trend analysis: a comparison of methods
Atmos. Environ.
Control of solute concentrations in cloud and fog water by liquid water content
Atmos. Environ.
Fog frequency and chemical composition of fog water – a relevant contribution to atmospheric deposition in the eastern Erzgebirge, Germany
Atmos. Environ.
Cloud chemistry measurements and estimates of acidic deposition on an above cloudbase coniferous forest
Atmos. Environ. A General Top.
Measurements of fog composition at a rural site
Atmos. Environ.
Formation of secondary organic carbon and cloud impact on carbonaceous aerosols at Mount Tai, North China
Atmos. Environ.
O/C and OM/OC ratios of primary, secondary, and ambient organic aerosols with high-resolution time-of-flight aerosol mass spectrometry
Environ. Sci. Technol.
Potential bronchoconstrictor stimuli in acid fog
Environ. Health Perspect.
Carbon speciation and surface-tension of fog
Environ. Sci. Technol.
Real-time secondary aerosol formation during a fog event in London
Atmos. Chem. Phys.
Characterization of water-soluble organic compounds in atmospheric aerosol: a new approach
J. Geophys. Res. Atmos.
Pollutant transfer in upland regions by occult precipitation
Nature
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Present affiliation: Proambiente S.c.r.l., CNR Research Area, Bologna, Italy.