Modal characteristics of particulate matter in urban atmospheric aerosols

Abstract

As part of an urban aerosol study, elemental mass size distributions and atmospheric mass concentrations of particulate matter (PM) were experimentally determined at four different locations in Budapest, Hungary, comprising an urban background site (KFKI campus), two downtown sites (Lágymányos campus and Széna Square) and a road tunnel (Castle District Tunnel, CD Tunnel). The analytical results available were utilized in the present work to derive size distributions of PM. Mass, surface area and particle number size distributions of PM for the accumulation and coarse modes, the total distributions, and the modal parameters are presented and discussed. The aerosol mass is always found predominantly in the coarse mode, and the ratio of the masses for the coarse and accumulation modes has an increasing tendency with the aerosol mass concentration. Fraction PM 10 contributes 83, 82, 69 and 69% of the total suspended particulate in the order of the sampling sites: KFKI campus, Lágymányos campus, Széna Square and CD Tunnel, respectively, while PM 2.5 makes up 55, 62, 40 and 34% of PM 10, respectively. Mass concentration of PM 0.1 fraction is only between 1.5 and 2.1% of the PM 2.5. The coarse and accumulation modes cross each other between 1.0 and 1.6 μm aerodynamic diameter, which is significantly smaller than the 50% cut-off value prescribed for the PM 2.5 samplers. It is the accumulation mode that represents the main surface area at all urban environments. The distributions of PM derived in the present paper are required for further studies.