Aerosol number concentrations and size distributions at mountain-rural, urban-influenced rural, and urban-background sites in Germany

Long-term aerosol measurements have been made at three sites in Germany, representing different levels of pollution: Hohenpeissenberg (mountain-rural), Melpitz (urban-influenced rural), and Leipzig (urban background). (Urban background aerosol represents a mixture of aerosols emitted in the city and aerosols transported into the city measured at a site with no direct emissions nearby.) To provide data that will allow better estimates of the influence of environmental aerosol particles on humans, we review diurnal variations of mean total number concentrations and size distributions of submicrometer environmental aerosol particles (including ultrafine particles smaller than 100 nm) for winter and summer periods in these three regions. Number concentrations and size distributions are compared and related to peak traffic periods and to meteorologically induced new-particle formation processes. The number concentration increase with increasing level of pollution. The mountain-rural site shows the smallest and the urban background site the highest number concentration. The relative diurnal variation of the number concentration between day and night, however, is for all sites nearly the same. Generally, traffic-related number concentration during rush-hour periods peaks in the size range of 20-30 nm. Due to weaker atmospheric convective processes in winter, this traffic-related aerosol is more pronounced than that in summer. In summer, meteorologically induced new-particle formation processes add another number concentration peak to the aerosol near 10 nm. This peak occurs near noon, independent of the day of the week. For the mean number concentrations and size distribution, this new-particle formation process was only relevant for the urban-influenced rural and the urban-background sites.