hide
Free keywords:
aerosol size distribution; secondary aerosol; single particle analysis; sulphur dioxide oxidation; urban plume
Abstract:
The change of the chemical composition of the near-ground level atmospheric aerosol
was studied during two summer episodes by a Lagrangian type of experimental approach. Bulk and
single-particle chemical analyses of ions and elements in the particulate phase were deployed. N(-III)
and N(V) components were also measured in the gas-phase. The measurements were completed by
particle size distributions.
Secondary inorganic aerosols (SIA) and fine particles of ≈0.2–0.4 µm size were still elevated
50 km downwind of the city. The direct comparison of transport over the city in contrast to transport
over the surrounding areas showed that SIA was formed from emission from the city within less than
3 h. Relative increases, i.e., enrichment during transport were observed for primary and secondary
aerosol components. The degree of mixing on the individual particle level increased significantly
during transport in the area. In particular, newly emitted carbonaceous particles became internally
mixed within hours with pre-existing sulphate particles. Mostly due to secondary aerosol formation
the average particle size (mass median diameter) of major constituents of the aerosol was significantly
decreased while being transported over 13 h. Given recent insights which link fine particles number
and mass concentrations with health risks, the results suggest that rural populations in areas which
frequently are located within an urban plume might run an elevated health risk relative to populations
in areas not affected by urban plumes.
