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

Abstract

Here we compare PM_2.5 (particles with aerodynamic diameter less than 2.5 μm) 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 PM₁₀ (particles with aerodynamic diameter less than 10 μm) 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 PM₁₀ and PM_2.5 was high, documenting that most of the spatial variation of PM₁₀ 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 PM₁₀ mass ranged from 0.54 to 0.68, the ratio of PM_2.5 absorbance and PM₁₀ absorbance was 0.96–0.97, indicating that PM_2.5 absorbance captures nearly all of the particle absorbance.