Analysis of PM-related measurements for the impacts of ships

The objective of this project is to resolve the sources of PM2.5 along the western coast of the United States with a particular emphasis on the impacts of ship emissions on the mass concentrations observed. Ship engines burn low cost, residual oil similar to that used in oil-fired power plants. The ability of these analyses to separately apportion the impacts of ships, sparkand compression-ignition vehicle emissions as well as the formation of secondary particles will be important to permit the assessment of the effects of ship emissions on air quality along this coast. The data that are available for these analyses include results from a number of sites that might be affected by ship emissions. Along the west coast, there are data available from three monitoring programs, IMPROVE, Speciation Trends Network (STN), and PM10 Technical Enhancement Program (PTEP). However, problems were found in the PTEP data and they were not analyzed. The IMPROVE and STN data were analyzed using positive matrix factorization. Applying these approaches to the PM-related measurements to identify PM sources was the goal of this study so that ship emission impacts can be quantitatively assessed. Primary emissions from the combustion of residual oil produce particles containing Ni and V. Source profiles for residual oil could be observed in Seattle, Los Angeles, and San Diego. They could not be identified at the other STN sites (Anchorage, Portland, and San Jose). There were high Ni concentrations in San Jose, but no V and thus, it is highly unlikely that this source is residual oil. The clearest influence of ship emissions was in Seattle where multiple site results point clearly to the Port of Seattle as a likely source area. The situation in the Los Angeles area is unclear. A residual oil profile could not be extracted from any of the three STN sites although Ni and V could be observed in approximately the ratio seen in the residual oil combustion profiles from other locations. The average Ni and V concentrations at Rubidoux were approximately 66% of those observed at the downtown LA site. If the source was ship emissions at the Port of Los Angeles and the Port of Long Beach, there should have been a much larger decrease in the Ni and V concentrations as the air moved eastward to Rubidoux. In addition, experiments performed in Rubidoux in the summer of 2005 found high concentrations of Vbearing particles and high mercury concentrations suggesting that there is significant residual oil combustion in the Riverside-Rubidoux area even though it does not appear in the emissions inventory. In addition, there is the potential confounding of the ship emissions by the refineries in the Torrence area. The emissions inventory indicates an emission rate for Ni of 750 pounds per year and no report of V emissions. However, it is likely that the Ni comes from residual oil combustion to produce the energy needed for the refinery operations. At all three sites, the Ni and V appear most strongly in the aged sea salt factor so that it appears there is sufficient covariance among these elements and Na and nitrate that they cannot be separated. At the two San Diego area sites, residual oil could be separated. At some of the rural IMPROVE sites (Aqua Tibia, San Rafael, Point Reyes, and Olympic), oil combustion source profiles can be identified. The clearest influence is at the Point Reyes National Seashore where it appears that the ships approaching San Francisco influence this site to the northwest of the city. However, primary ship emissions do not represent a large source of PM2.5 at any site with a maximum mean value of the order of 1 μg/m . A correlation between the primary oil combustion particles and secondary sulfate could be identified at a number of sites. In Seattle, there appears to be 0.82 μg/m of sulfate for every 1 μg/m of primary oil combustion particles. However, in San Diego, a similar correlation could not be observed. At Point Reyes National Seashore, the relationship between the ship emission primary particles and secondary sulfate is less well defined as obsered in Seattle. If there is a relationship, it has similar magnitude to that was more clearly seen in Seattle. The results for the Aqua Tibia, San Rafael, and Olympic sites are more equivocal. Thus, the presence of other sources of secondary sulfate tend to mask the production of sulfate aerosol arising from ship emissions.