Concentrations in Ambient Air and Emissions of Cyclic Volatile Methylsiloxanes in Zurich, Switzerland

Tens of thousands of tonnes of cyclic volatile methylsiloxanes (cVMS) are used each year globally, which leads to high and continuous cVMS emissions to air. However, field measurements of cVMS in air and empirical information about emission rates to air are still limited. Here we present measurements of decamethylcyclopentasiloxane (D₅) and dodecamethylcyclohexasiloxane (D₆) in air for Zurich, Switzerland. The measurements were performed in January and February 2011 over a period of eight days and at two sites (city center and background) with a temporal resolution of 6–12 h. Concentrations of D₅ and D₆ are higher in the center of Zurich and range from 100 to 650 ng m^–3 and from 10 to 79 ng m^–3, respectively. These values are among the highest levels of D₅ and D₆ reported in the literature. In a second step, we used a multimedia environmental fate model parametrized for the region of Zurich to interpret the levels and time trends in the cVMS concentrations and to back-calculate the emission rates of D₅ and D₆ from the city of Zurich. The average emission rates obtained for D₅ and D₆ are 120 kg d^–1 and 14 kg d^–1, respectively, which corresponds to per-capita emissions of 310 mg capita^–1 d^–1 for D₅ and 36 mg capita^–1 d^–1 for D<sub>6