A comparative study on the varying exposure to atmospheric fine and coarse particles under urban and rural conditions

Abstract

This paper is based on the results of three air quality studies conducted in Buenos Aires in Berlin, and in German spas between 2003 and 2007. A high comparability of results was ensured by using the same sampling techniques and analytical methods. Total particle sampling was achieved by active sampling of fine (PM2.5) and passive sampling of coarse particles ≥2.5 µm and giant particles ≥10 µm. The highly absorbing, black, predominantly carbonaceous particles (BC) of fine particle samples were determined by measuring the total light attenuation of filter samples and interpreting the extinction value as black carbon. The difference between the gravimetric total mass concentration of the PM2.5 samples and the BC is defined as the transparent, mostly mineral fine fraction. In coarse/giant particle samples the mean gray value was determined by means of automated light microscopy with subsequent single-particle analysis. “Opaque” particles were separated from the “transparent” particle fraction by applying a grey value threshold level. Microscopic measurement of individual particles was employed to establish the size distribution of the coarse and giant fraction. Due to different health effects, the separate detection of these components is suggested. Decline functions of particles are given, possibly providing useful information for a more detailed specification of the local particle distribution, and for a better estimate of the individual exposure. Atmospheric dispersal of particles was found effected mainly by source characteristics. An increased, spatially largely constant level of fine transparent particles in Berlin indicates a particle plume originating from photochemical processes. Buenos Aires, in contrast, is characterized by a lower background level of fine transparent particles but is considerably affected by fine black particles from diesel emissions and by a higher resuspension of coarse/giant transparent, mainly soil particles. Implications: Mini-volume and passive sampling combined proved to be suitable for measuring total particles by collecting fine, coarse, and giant particles. This approach allows the acquisition of highly space-resolved data on a weekly basis. A method was employed to calculate a size-fractionated particle concentration from passive samples. The results from three air quality studies using this method demonstrate that the black/opaque and transparent particles distinguished differ considerably in spatial distribution, not only due to varying atmospheric residence. Estimates of the exposure of humans, therefore, have to consider the different effects of rural and urban conditions, and differences between regional climates.