The weekly cycle of ambient concentrations and traffic emissions of coarse (PM10–PM2.5) atmospheric particles

The aim of the study is to investigate the existence of a weekly cycle of coarse mode (PM10–PM2.5) atmospheric particles, to compare this weekly cycle to the weekly cycle of PM2.5 and to compare the strength of the coarse mode weekly cycle in different seasons and different wind speed, wind direction and precipitation conditions. In addition, an estimate of the contribution of traffic to the total ambient coarse mode particulate matter in Zurich, Switzerland is provided by estimating the weekly cycle of coarse mode traffic emissions and by comparing it to the weekly cycle of ambient concentrations. The coarse mode data used in the study are the result of simultaneous daily measurements of PM10 and PM2.5 at seven sites located in Switzerland. The measurements cover a period of 7–12 years for six stations and 3 years for one station. It is found that a coarse mode weekly cycle is present in various types of urban and rural stations. Ambient concentrations on weekdays are higher than on Sundays by a factor of 1.53 on average over all urban and suburban sites and by a factor of 1.32 on average over all rural sites. Moreover, the relative increase of coarse mode ambient concentrations on weekdays compared to Sundays was larger than the relative increase of PM2.5 concentrations by a factor of 2.7 on average over all urban and suburban sites, whereas no considerable difference was found at the rural sites. A calculation of coarse mode traffic emissions for an urban scenario was carried out using traffic-induced dust resuspension and brake wear emission factors for light and heavy duty vehicles and traffic counts from Zurich, Switzerland. It is shown that coarse mode emissions on weekdays are greater than on Sundays by a factor of 2.0. The contribution of traffic to coarse mode urban ambient concentrations was estimated to be 53% (34%–78%) on Sundays and 70% (57%–86%) on weekdays. It is deemed however that these numbers are somewhat overestimating the traffic contribution because of lack of information on construction activities around the considered sites.