Modeling air pollution in Venice

Rapporto Tecnico CS-2009-1, Dipartimento di Informatica, Universita' Ca' Foscari di Venezi

GC-MS analyses and chemometric processing to discriminate the local and long-distance sources of PAHs associated to atmospheric PM2.5

Purpose . This study presents a procedure to differentiate the local and remote sources of particulate-bound polycyclic aromatic hydrocarbons (PAHs). Methods. Data were collected during an extended PM2.5 sampling campaign (2009–2010) carried out for 1 year in Venice-Mestre, Italy, at three stations with different emissive scenarios: urban, industrial, and semirural background. Diagnostic ratios and factor analysis were initially applied to point out the most probable sources. In a second step, the areal distribution of the identified sources was studied by applying the discriminant analysis on factor scores. Third, samples collected in days with similar atmospheric circulation patterns were grouped using a cluster analysis on wind data. Local contributions to PM2.5 and PAHs were then assessed by interpreting cluster results with chemical data. Results. Results evidenced that significantly lower levels of PM2.5 and PAHs were found when faster winds changed air masses, whereas in presence of scarce ventilation, locally emitted pollutants were trapped and concentrations increased. This way, an estimation of pollutant loads due to local sources can be derived from data collected in days with similar wind patterns. Long-range contributions were detected by a cluster analysis on the air mass back-trajectories. Results revealed that PM2.5 concentrations were relatively high when air masses had passed over the Po Valley. However, external sources do not significantly contribute to the PAHs load. Conclusions. The proposed procedure can be applied to other environments with minor modifications, and the obtained information can be useful to design local and national air pollution control strategies

Il materiale legnoso in corsi d'acqua a canali intrecciati: volumi, mobilità , degradazione ed influenza morfologica

Natural wood in rivers has received wider attention in the scientific community only over the past two decades from different perspectives (biological, geomorphological and engineering). Wood has been studied mostly in mountain basins whereas large rivers have been less investigated. The present research deals with different aspects related to in-channel wood in gravel bed rivers, including physical wood characteristics, wood storage and transport, and link between wood abundance and river morphology. The analysis of physical characteristics of wood was carried out in three rivers: the Piave River (Veneto, Italy), the Magra River (Toscana, Italy) and the Ain River (Rhône- Alpe, France). Different variables were compared for a specific species (Populus nigra). Mean wood density range from 0.25 to 0.35 g/cm3, with Ain’s values differing significantly from the other rivers. The age of sampled wood elements is similar in the Piave and in the Magra (16 and 17 yr, respectively), whereas Ain’s samples are much older (31 yr). The growth coefficient si instead similar for the three rivers, but resistance to penetration is significantly higher in the Piave and presents a positive correlation with sample’s age. As to wood transport, 10 logs were tagged with metal tags and radiofrequency transmitters to monitor their mobility. Unfortunately, the 2005 fall season was very dry and no significant events occurred, also the 2006 spring snowmelt runoff did not reach a sufficient stage to mobilize the tagged logs. In September 2006, the largest event of the year (below bankfull stage) did not reach the logs, but the bar erosion taking place near one tagged log caused its recruitment into the flow and its transport downstream. Transport distance was about 4 km, i.e. about 18 times the mean channel width. The wood storage survey has regarded a 30 km reach in the Piave river between Ponte nelle Alpi and Busche (Belluno). Here the rivers features braided and wandering morphologies. Two integrated methods were implemented: field measurements in selected plots and interpretation of high-resolution (10 cm pixel) aerial photos at the reach scale.. Errors associated to wood measurements by using aerial photographs were evaluated the field plots. Results are encouraging, showing a good potential and efficiency of such approach for rivers where a total field survey would be unfeasible (ED 20 cm). The analysis based on aerial photos led to estimate average wood load to be within the range 3.7 – 9.1 m3/ha, depending on how wood jam volume is computed. Single wood elements present a mean diameter of 28 cm and a mean length of 7.5 m. Tree species indicate most of the wood derives from the riparian corridor but other species are also present due to lateral erosion of recent low terraces. The analysis of wood storage at different reaches showed that wood is more abundant in braided channel more than in wandering reaches. Wood is mostly located on bars (rather equally in high and low ones), but a considerable fraction of wood is associated to islands in the wider braided reaches. A strong negative correlation is present between single wood elements’ volume and relative area occupied by low flow channels, whereas wood jam volume is strongly correlated with the relative area of islands

Secondary inorganic aerosol evaluation: Application of a transport chemical model in the eastern part of the Po Valley

Secondary inorganic aerosol (SIA) represents an important component of fine particulate matter in Europe. A photochemical model has been used to assess the distribution of secondary inorganic ions (sulfate, nitrate and ammonium) in the eastern part of the Po Valley, close to Venice. Specific meteorological and environmental conditions and very highly urbanized and industrialized areas make this domain one of the most polluted in Europe. Several studies have been conducted to assess particulate matter (PM10 and PM2.5) areal distribution. However, SIA formation dynamics are still a research subject especially in the transition environments, where the changes in the orography and in the land-use can affect air mass movements and atmospheric composition. This paper is a first attempt to simulate SIA distribution by using a photochemical model in the sea/land Venice transition area. Moreover, a modeling approach with clean boundary conditions has been used to check local and regional influence on SIA levels in the domain. Results reveal that, despite the importance of regional influences, local formation processes are important in SIA distribution especially during warm periods. SO42- and NH4+ are more linked to emission sources distribution than NOT that tends to be more diffused in the study area. The use of a photochemical model, suitably tested in a such complex area, can improve air pollution knowledge and can help in air quality decision making