UCLA

A-weighted equivalent continuous sound level (LeqA), ultrafine particles (UFP, particles with aerodynamic diameter < 100 nm) number concentrations, and fine particles (particles with aerodynamic diameter < 2.5 um) mass concentrations were measured simultaneously at increasing distances from the freeways on four streets in Los Angeles, CA, with or without sound wall, from February to June 2013. Correlations among UFP number concentrations, PM2.5 mass concentrations and LeqA were assessed by Pearson correlation coefficient. The impacts of wind direction, traffic volume and the presence of sound wall on PM2.5 mass concentrations, UFP number concentrations and LeqA were also investigated.

Moderate correlation(r ranges from 0.514 to 0.605, p<0.05) between LeqA and UFP number concentrations were observed under downwind conditions on all four streets. However, no correlation was found under upwind conditions. PM2.5 mass concentrations were correlated with UFP number concentration, but not with LeqA. The sound wall was effective at blocking noise but its ability to block particulate matters needs further investigation. It suggests that the residents and workers who live or work at the dominantly downwind side of freeway are exposed to higher UFP yet similar noise levels when comparing with the situations at the upwind side of freeway. In addition, it is feasible to use the upwind side of freeway as a control for the two common confounders, particulate matters and noise, in epidemiological and occupational exposure studies. Data generated in this study may be used to study the independent and synergistic health impacts of noise and particulate matters near freeways, especially from an occupational exposure perspective for near roadside workers such as traffic directing personnel, gas station personnel and toll station workers.