Concentrations and Fate of Decamethylcyclopentasiloxane (D<sub>5</sub>) in the Atmosphere

Decamethylcyclopentasiloxane (D<sub>5</sub>) is a volatile compound used in personal care products that is released to the atmosphere in large quantities. Although D<sub>5</sub> is currently under consideration for regulation, there have been no field investigations of its atmospheric fate. We employed a recently developed, quality assured method to measure D<sub>5</sub> concentration in ambient air at a rural site in Sweden. The samples were collected with daily resolution between January and June 2009. The D<sub>5</sub> concentration ranged from 0.3 to 9 ng m<sup>−3</sup>, which is 1−3 orders of magnitude lower than previous reports. The measured data were compared with D<sub>5</sub> concentrations predicted using an atmospheric circulation model that included both OH radical and D<sub>5</sub> chemistry. The model was parametrized using emissions estimates and physical chemical properties determined in laboratory experiments. There was good agreement between the measured and modeled D<sub>5</sub> concentrations. The results show that D<sub>5</sub> is clearly subject to long-range atmospheric transport, but that it is also effectively removed from the atmosphere via phototransformation. Atmospheric deposition has little influence on the atmospheric fate. The good agreement between the model predictions and the field observations indicates that there is a good understanding of the major factors governing D<sub>5</sub> concentrations in the atmosphere.