High sulfur dioxide deposition velocities measured with the flux–gradient technique in a boreal forest in the Alberta Oil Sands Region

This is the authors' abstract. We don't add key points for this paper.

The emission of SO 2 from the Athabasca Oil Sands Region (AOSR) has been shown to impact the surrounding forest area. Recent studies using aircraft-based measurements have demonstrated that deposition of SO 2 to the forest is at a rate many times higher than model estimates. Here we use the flux–gradient method to estimate SO 2 deposition rates at two tower sites in the boreal forest downwind of AOSR SO 2 emissions. We use both continuous and passive sampler measurements and compare the two techniques. The measurements infer SO 2 deposition velocities ranging from 2.1–5.9 cm s −1 (when corrections are applied). There are uncertainties associated with the passive sampler flux–gradient analysis, primarily due to an assumed Schmidt number, a required assumption of independent variables, and potential wind effects. We estimate the total uncertainty as ± 2 cm s −1 . Accounting for these uncertainties, the range of measurements is approximately double the previous aircraft-based measurements (1.2–3.4 cm s −1 ) and more than 10 times higher than model estimates for the same measurement periods (0.1–0.6 cm s −1 ), suggesting that SO 2 in the AOSR has a much shorter lifetime in the atmosphere than is currently predicted by models.