Mobile measurements of aerosol number and volume size distributions in an Alpine valley: Influence of traffic versus wood burning

The spatial variability of highly time resolved size distributions was investigated in a narrow valley which provides the opportunity to study the impact of different sources on ambient particle concentrations during summer and winter time. The measurements were performed with a Fast Mobility Particle Sizer (FMPS) from TSI, Inc. on a mobile laboratory in Southern Switzerland. The results indicate enhanced number concentrations (between 150 000 and 500 000 cm−3) along the busy highway A2 which is the main transit route through the Swiss Alps connecting the northern and southern part of Switzerland. Especially the nanoparticles with diameters lower than 30 nm showed strongly increased number concentrations on the highway both in summer and winter. In winter time, high aerosol volume concentrations (PM0.3) were found in villages where wood burning is often used for heating purposes. Both traffic and wood burning were found to be important sources for particulate mass which accumulates during temperature inversions in winter time. Traffic was the dominant and wood burning a minor source for the nanoparticle number concentration. This is important regarding health impacts and its attribution to different sources because wood burning might contribute most to particulate mass whereas at the same time and place traffic contributes most to particulate number. In addition, during summer time volatility measurements were performed with the FMPS showing that the nucleation mode prevalently seen on the highway was removed by more than 95% by thermal treatment.