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Measurements of airborne particles with aerodynamic diameter of 10 μm or less (PM<sub>10</sub>) and meteorological observations are available from 13 stations distributed throughout Switzerland and representing different site types. The effect of all available meteorological variables on PM<sub>10</sub> concentrations was estimated using Generalized Additive Models. Data from each season were treated separately. The most important variables affecting PM<sub>10</sub> concentrations in winter, autumn and spring were wind gust, the precipitation rate of the previous day, the precipitation rate of the current day and the boundary layer depth. In summer, the most important variables were wind gust, Julian day and afternoon temperature. In addition, temperature was important in winter. A "weekend effect" was identified due to the selection of variable "day of the week" for some stations. Thursday contributes to an increase of 13% whereas Sunday contributes to a reduction of 12% of PM<sub>10</sub> concentrations compared to Monday on average over 9 stations for the yearly data. The estimated effects of meteorological variables were removed from the measured PM<sub>10</sub> values to obtain the PM<sub>10</sub> variability and trends due to other factors and processes, mainly PM<sub>10</sub> emissions and formation of secondary PM<sub>10</sub> due to trace gas emissions. After applying this process, the PM<sub>10</sub> variability was much lower, especially in winter where the ratio of adjusted over measured mean squared error was 0.27 on average over all considered sites. Moreover, PM<sub>10</sub> trends in winter were more negative after the adjustment for meteorology and they ranged between −1.25 μg m<sup>−3</sup> yr<sup>−1</sup> and 0.07 μg m<sup>−3</sup> yr<sup>−1</sup>. The adjusted trends for the other seasons ranged between −1.34 μg m<sup>−3</sup> yr<sup>−1</sup> and −0.26 μg m<sup>−3</sup> yr<sup>−1</sup> in spring, −1.40 μg m<sup>−3</sup> yr<sup>−1</sup> and −0.28 μg m<sup>−3</sup> yr<sup>−1</sup> in summer and −1.28 μg m<sup>−3</sup> yr<sup>−1</sup> and −0.11 μg m<sup>−3</sup> yr<sup>−1</sup> in autumn. The estimated trends of meteorologically adjusted PM<sub>10</sub> were in general non-linear. The two urban street sites considered in the study, Bern and Lausanne, experienced the largest reduction in measured and adjusted PM<sub>10</sub> concentrations. This indicates a verifiable effect of traffic emission reduction strategies implemented during the past two decades. The average adjusted yearly trends for rural, urban background and urban street stations were −0.37, −0.53 and −1.2 μg m<sup>−3</sup> yr<sup>−1</sup> respectively. The adjusted yearly trends for all stations range from −0.15 μg m<sup>−3</sup> yr<sup>−1</sup> to −1.2 μg m<sup>−3</sup> yr<sup>−1</sup> or −1.2% yr<sup>−1</sup> to −3.3% yr<sup>−1</sup>.

_{10}and coarse particles at urban, near-city and rural sites in Switzerland, Atmos. Environ., 39, 637–651, 2005.]]>

_{2.5}and PM

_{1}at the IfT research station Melpitz dowinwind of Leipzig (Germany) using high and low-volume filter samplers, Atmos. Environ., 38, 5333–5347, 2004.]]>

_{10}concentrations in the Netherlands and its relation with EU limit values, Atmos. Environ., 43, 3858–3866, 2009.]]>