Abstract:
The EPA has recently funded a project proposed by the Puget Sound Clean Air Agency (PSCAA) to develop improved methods of source apportionment of air toxics. The project, entitled "Evaluation of Methods for Air Toxics Source Apportionment Using Real-Time Continuous Monitoring Instruments," is motivated by a growing need to improve characterization of air toxics emission sources within the current air monitoring system in Puget Sound. A risk evaluation performed in 2003 by PSCAA found diesel particulate matter (DPM) to be responsible for as much as 75-80% of total cancer risk due to air toxics. Due to the proclivity of DPM to cause cancer relative to other air toxics, it is given the utmost priority for monitoring and control. DPM sources arise from a wide range of transportation modes, such as by railroad, many types of heavy equipment, vehicles on the highway, and marine vessels that travel through the Puget Sound and moor at one of the many ports. As the extent to which marine vessel activities impact local populations is the least understood amont these source types, the objective of this project was to develop a method for modeling marine emissions. In this study, atmospheric dispersion modeling with CALPUFF was used to model the emissions from a specific vessel as it travels in and out of the Puget Sound to Harbor Island. Signals derived from the Automated Identification System (AIS) that carry information about the vessel's identification, speed, position, and status were used to establish a series of point sources along the vessel's track, modeling the vessel as a mobile point source. The concentration fields resulting from this vessel's activity were modeled for four meteorological conditions, with one example for each season.