The mass concentrations of PM2.5 (particles with aerodynamic diameter < 2.5 um), number concentration of ultrafine particles (UFP, particles with aerodynamic diameter < 100 nm), concentrations of carbon dioxide (CO2), as well as mass concentrations of black carbon (BC, results from incomplete combustion of fossil fuels and biomass, usually consists of several linked carbon atoms, commonly referred to as "soot") were measured near the Peking University (PKU) campus in Beijing from December 10th to December 23rd, 2011. Correlation between UFP number concentrations and PM2.5 mass concentrations, as well as PM2.5 mass concentrations and BC mass concentrations were determined while taking into consideration the local meteorological conditions and traffic densities determined from recorded video footage. Traffic emissions were calculated using ultrafine particle number concentration (PNC) and CO2 concentrations. The PM2.5 mass concentration, PNC, BC mass concentration as well as calculated traffic emission data were compared with existing data for the Los Angeles metropolitan region. The differences and similarities between the two data sets were compared and discussed.
No correlation was found between PNC and PM2.5 mass concentrations. However, a high correlation between BC and PM2.5 mass concentrations was found. Also, correlations were identified between local meteorological conditions such as wind direction and PNC, PM2.5, and BC mass concentrations near roadways, especially when the site was downwind of local traffic. No correlation was found between wind speed and PNC, although strong correlations were found between wind speed and PM2.5, as well as BC mass concentrations. Days where both PM2.5 mass concentrations and PNC were higher at the control site were observed to be wind direction dependent, indicating the detection of regional emission sources. A strong correlation between PM2.5 mass concentrations and local visibility was also demonstrated. In terms of traffic, total traffic had almost no correlation with PNC. However, total diesel traffic was found to have some correlation to PNC, with higher diesel vehicle volume correlating to higher PNC. Finally, from the comparison between Los Angeles and Beijing data sets, Beijing tends to have higher emission factors, as well as near roadway PNC and PM2.5 mass concentrations, after controlling for wind direction.
Data generated from this study could be used to model near roadway exposures to PM2.5 as well as UFP, especially from an occupational exposure standpoint for roadside workers such as food stand workers, traffic directing personnel, among others.
