The effects of heavy-duty drayage truck fleet modernization and diesel particle filter (DPF) retrofits were examined through measurements of truck emissions near the Port of Oakland. Pollutant concentrations were measured at high time resolution in the exhaust plumes of more than a thousand drayage trucks as they drove toward the Port on a major access road. Emission factors were matched to data from a statewide drayage truck registry, including engine make, model year, and installed emission control equipment, using recorded license plates for each truck. Between 2009 and 2013, Phase 1 of California's Drayage Truck Regulation led to an increase in Port trucks equipped with DPFs (the fraction so equipped rose from 2 to 99%), and a decrease in median engine age from 11 to 6 years. Over the same period, fleet-average emission factors decreased by 76 ± 22% and 53 ± 8% for black carbon (BC) and oxides of nitrogen (NOx), respectively. However, direct emissions of nitrogen dioxide (NO2) increased, and consequently the NO2/NOx emission ratio increased from 0.03 ± 0.02 to 0.18 ± 0.03. DPF-equipped trucks had substantially lower BC and higher NO2 emission factors than trucks without DPFs. The newest trucks equipped with both DPFs and selective catalytic reduction (SCR) systems for NOx control had the lowest average emission factors for BC and ultrafine particles (UFP), and an average NO2 emission factor that was about equal to that of the Port truck fleet that was on the road in 2009 before recent emission regulations took effect. Phase 2 requirements, implemented in 2014, led to replacement of nearly one third of the 2013 Port truck fleet (until then mainly pre-2007 engines have been replaced with newer engines equipped with SCR). In part two of this project, additional measurements of drayage truck emissions at the Port of Oakland were made in 2015 to quantify the emission impacts of increasingly widespread use of SCR for controlling NOx emissions from on-road diesel engines. The fraction of trucks equipped with SCR increase from 9% to 25% from 2013 to 2015, and the fleet-averages NOx emission factor decreased by 36% ± 7% during this time period.
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