PAHs and Trace Elements in PM2.5 at the Venice Lagoon

The results of an experimental analysis carried out to investigate PM_2.5 concentration levels and the content of polycyclic aromatic hydrocarbons, as well as inorganic trace elements in the atmospheric particles are presented. Measurements were taken with a micrometeorological station equipped with an optical PM_2.5 detector, and simultaneously, particles were collected on filters for subsequent chemical analyses. The average value of daily PM_2.5 concentration is 21.5 ug/m3 and real-time measurements indicate that the average concentration during the day (8 am to 8 pm) is about 25 % lower than the nocturnal average. Short-time averages of PM_2.5 decrease when the wind speed increases as consequence of the more efficient mixing. Meteorological measurements indicate the presence of a local daily (breeze) circulation with wind blowing from the Alps or the Adriatic Sea and, during this circulation, larger concentrations were observed, with wind coming from the Alps. Days of high PM_2.5 concentration with dominant anthropic or with prevalent crustal contributions were identified.

Regarding trace metals, their average concentrations are comparable to those found in others urban areas, except for Cd (3 ng m^-3), probably due to the presence of glass-works in Murano. The highest concentrations are observed for K (99 ng m^-3) and Na (73 ng m^-3), which are the main constituents of marine spray, while the lowest concentrations are observed for elements such as Cs and Co (respectively 0.01 and 0.02 ng m^-3). Also the concentrations of PAH are comparable with those of other industrial areas, as their sum ranges from 0.16 ng m^-3 to 3.73 ng m^-3, but if considered as B(a)P toxicity equivalent, they are largely lower (0.036±0.026 ng m^-3). From the analyses of discriminating ratios, it has been found that the main origin of PAH in PM_2.5 samples may be petrogenic, probably related to the presence of refinery and petrochemical plants on the mainland, although the contribution of combustion processes cannot be excluded.