Evaluation of vessel emissions in a lagoon area with ground based Multi axis DOAS measurements

The environmental impact of large vessel exhaust gases on port and coastal areas is a subject of great interest due both to increasing maritime traffic and the vicinity to highly populated urban zones. In lagoon cities the pollution from maritime traffic is greater than in other coastal areas. Therefore monitoring and evaluation of pollutants produced by ships navigating through the principal transport channels become necessary. In the case of Venice, the Giudecca Channel, crossing the city centre, is used both by urban maritime traffic and by large vessels docking in the port.In this work, the FRE–DOAS (Flow Rate Emission with Differential Optical Absorption Spectroscopy) methodology developed to evaluate gaseous pollutant flow rates from moving sources is presented. This methodology is applied to a set of spectral measurements performed with a Multi axis DOAS remote sensing system, allowing a determination of vessel emissions and evaluation of their impact on pollution in Venice.Two one-month measurement campaigns were carried out: from June 12 2007 to July 12 2007 and from September 12 2007 to October 12 2007. The individual flow rates released by large and medium-sized vessels and the total flow rate emissions due to the total traffic along the Giudecca Channel for every day with appropriate meteo conditions during the campaigns are estimated.The average daily mass of gas emitted by large and medium-sized ships during their passage through the Channel was evaluated as about 205 kg for SO2 and 284 kg for NO2. These values make up only about 30% of total daily traffic emission. These results are extremely interesting, because they demonstrate inequivocably the effectiveness of the proposed system for remote measurements, opening a new frontier in maritime traffic emission control in harbour areas or in those coastal zones subject to heavy maritime traffic. Moreover, the low values obtained for some large modern cruise ships indicate the use of Low Sulphur Fuels, even though these are not yet required by local regulations.

► FRE–DOAS remote sensing method to measure gas flow rate with MAX-DOAS is proposed.
► The mathematical formulation of FRE–DOAS is widely explained.
► The method provided a measure of large ships impact along the main Venice artery.
► Its value was compared to the total traffic impact along the Giudecca Channel.
► The method, being an automatic one, can be used for control and inspective aims.