Comparison between different traffic-related particle indicators: elemental carbon (EC), PM2.5 mass, and absorbance

Here we compare PM(2.5) (particles with aerodynamic diameter less than 2.5 microm) mass and filter absorbance measurements with elemental carbon (EC) concentrations measured in parallel at the same site as well as collocated PM(2.5) and PM(10) (particles with aerodynamic diameter less than 10 microm) mass and absorbance measurements. The data were collected within the Traffic-Related Air Pollution on Childhood Asthma (TRAPCA) study in Germany, The Netherlands and Sweden. The study was designed to assess the health impact of spatial contrasts in long-term average concentrations. The measurement sites were distributed between background and traffic locations. Annual EC and PM(2.5) absorbance measurements were at traffic sites on average 43-84% and 26-76% higher, respectively, compared to urban background sites. The contrast for PM(2.5) mass measurements was lower (8-35%). The smaller contrast observed for PM(2.5) mass in comparison with PM(2.5) absorbance and EC documents that PM(2.5) mass underestimates exposure contrasts related to motorized traffic emissions. The correlation between PM(10) and PM(2.5) was high, documenting that most of the spatial variation of PM(10) was because of PM(2.5). The measurement of PM(2.5) absorbance was highly correlated with EC measurements and suggests that absorbance can be used as a simple, inexpensive and non-destructive method to estimate motorized traffic-related particulate air pollution. The EC/absorbance relation differed between countries and site type (background/traffic), supporting the need for site-specific calibrations of the simple absorbance method. While the ratio between PM(2.5) and PM(10) mass ranged from 0.54 to 0.68, the ratio of PM(2.5) absorbance and PM(10) absorbance was 0.96-0.97, indicating that PM(2.5) absorbance captures nearly all of the particle absorbance.