Direct measurements of size-segregated particle fluxes above a city

Atmospheric aerosol particles have major impacts on human health, direct and indirect negative forcing of the Earth's radiation budget, atmospheric chemistry as well as on long-range transport and deposition of pollutants, especially in remote areas. Owing to their physical properties and small number concentrations, the measurement of the surface/atmosphere exchange of aerosol particles, especially of the larger particles (Dp > 0.3 p.m), is very challenging. Our understanding of sources and sinks of aerosols, their deposition rates and deposition footprints is therefore still limited. Emissions are usually predicted using emission inventories that are based on activities and emission factors (.e.g. Salway et al., 1997). These emissions are used in atmospheric transport and deposition models and their uncertainties propagate into the quantification of deposition and concentration fields. We here present the first direct measurements of size-segregated particle fluxes above a city representative for a scale of several (100 m) 2. In this study the emission or deposition was measured directly with micrometeorological techniques and the controlling parameters were derived by footprint analysis as well as through comparison with meteorological parameters (e.g. wind speed and direction), traffic densities, potential precursor gas concentrations and PMIo concentrations at street level