Size-segregated composition of particulate matter (PM) in major roadways and surface streets

Abstract A sampling campaign was conducted to assess on-road particulate matter (PM) composition for three size fractions (PM 10 – 2.5 , PM 2.5 – 0.25 , and PM 0.25 ) on three representative roadways in Los Angeles: 1) the I-110, a high-traffic freeway composed mostly of light-duty vehicles (LDVs), 2) the I-710, a major freeway for heavy-duty vehicles (HDVs) traveling to and from the Ports of Los Angeles and Long Beach, and 3) Wilshire/Sunset Blvd, two major surface streets. Concurrent sampling was conducted at the University of Southern California (USC), which was used as an urban background site. Two sets of PM samples were collected for each roadway, with a sampling duration of approximately 50 h for each set. The samples were analyzed for inorganic ions, elemental carbon (EC), organic carbon (OC), water-soluble OC (WSOC), and trace elements and metals. Results showed that the PM 0.25 fraction is heavily influenced by on-road vehicular emissions, as indicated by average roadway PM concentrations that were 48.0 ± 9.4% higher than those observed at USC ( p 10 – 2.5 fraction is mostly influenced by resuspension of road dust and the PM 2.5 – 0.25 fraction is mainly composed of secondary species. Overall, the composition of inorganic ions (%) was relatively consistent across the three roadway environments. With very low EC levels in PM 10 – 2.5 , the most notable difference among the three roadway environments was the PM 2.5  EC levels observed on the I-710, which are 2.0 ± 0.2 μg m −3 and 4.1 times greater than USC, while levels on the I-110 and Wilshire/Sunset were 1.0 ± 0.2 μg m −3 and 0.6 ± 0.01 μg m −3 and 2.1 and 1.2 times greater, respectively. PM 2.5 OC and WSOC concentrations were observed to be 1.6, 2.0, and 1.7 times greater on the I-110, I-710, and Wilshire/Sunset than corresponding levels at USC, respectively. Results from this study may have major public health implications for passengers who commute frequently on high-traffic roadways. Finally, a comparison of EC levels to previous studies conducted at fixed sites near the I-110 and I-710 showed substantial decreases in EC concentrations over the past years, which may be a result of the recent Port of Los Angeles Clean Truck Program.