Emission changes resulting from the San Pedro Bay, California Ports Truck Retirement Program

Recent U.S. Environmental Protection Agency emissions regulations have resulted in lower emissions of particulate matter and oxides of nitrogen from heavy-duty diesel trucks. To accelerate fleet turnover the State of California in 2008 along with the Ports of Los Angeles and Long Beach (San Pedro Bay Ports) in 2006 passed regulations establishing timelines forcing the retirement of older diesel trucks. On-road emissions measurements of heavy-duty diesel trucks were collected over a three-year period, beginning in 2008, at a Port of Los Angeles location and an inland weigh station on the Riverside freeway (CA SR91). At the Port location the mean fleet age decreased from 12.7 years in April of 2008 to 2.5 years in May of 2010 with significant reductions in carbon monoxide (30%), oxides of nitrogen (48%) and infrared opacity (a measure of particulate matter, 54%). We also observed a 20-fold increase in ammonia emissions as a result of new, stoichiometrically combusted, liquefied natural gas powered trucks. These results compare with changes at our inland site where the average ages were 7.9 years in April of 2008 and 8.3 years in April of 2010, with only small reductions in oxides of nitrogen (10%) being statistically significant. Both locations have experienced significant increases in nitrogen dioxide emissions from new trucks equipped with diesel particle filters; raising the mean nitrogen dioxide to oxides of nitrogen ratios from less than 10% to more than 30% at the Riverside freeway location.