Measuring atmospheric dry deposition with large surrogate surfaces for improved time resolution

Surrogate surfaces are used to measure atmospheric dry deposition of contaminants and are sometimes designed intentionally with simple geometry to estimate the lower limit of the flux to any surface. However, most surrogate surfaces have a small collection area: long periods of dry weather may be needed to obtain sufficient deposited contaminants to be detected and quantified, and such exposure periods may not be common in wet climates. In this study, two relatively large surrogate surfaces—disks with surface areas >1 m²—were designed to measure dry deposition of F⁻, Cl⁻, SO₄²⁻, and NO₃⁻ in Syracuse, NY. Results indicate that good reproducibility is possible for measurements with exposure periods of 2–6 days. The ranges of dry deposition velocities for each species are as follows: F⁻ (0.6–2.5 cm/s), Cl⁻ (1.9–9.2 cm/s), SO₄²⁻ (0.11–1.8 cm/s), and NO₃⁻ (0.1–1.1 cm/s). Fluxes were also measured to four separate sections of the disk; results suggest that deposition varies somewhat across the disk in a way that is consistent with boundary layer thickness predicted by Computational Fluid Dynamics modeling.