Quantifying the dry deposition of reactive nitrogen and sulfur containing species in remote areas using a surrogate surface analysis approach

In this study, the fluxes of gaseous (HNO3 and SO2) and particulate (NO3− and SO42−) species were measured using two recently developed surrogate surfaces, the water surface sampler (WSS) and the knife-edge surrogate surface (KSS). Sampling was conducted in Potsdam, NY, Solomons, MD, and at a farm in upstate NY intermittently between March 2000 and August 2001. The KSS contained both Nylasorb filters and greased Mylar disks. No statistical difference was found between measured total nitrate and sulfate deposition in side-by-side experiments with two WSSs. Average total nitrate fluxes measured with the WSS and Nylasorb filter on the KSS in Potsdam, Solomons, and at the farm were 3.6, 6.2, 2.9 mg m−2 day−1 and 2.5, 6.7, 2.3 mg m−2 day−1, respectively. Solomons had the highest total nitrate flux probably due to its proximity to large urban industrialized areas including Washington, DC, and Baltimore, MD. Average gaseous HNO3 fluxes measured with the WSS and Nylasorb filter on the KSS in Potsdam, Solomons, and at the farm (calculated by subtracting the fraction of particles deposited to the Mylar disk from the total deposition to the WSS and Nylasorb filter) were 2.4, 4.9, 1.9 mg m−2 day−1 and 1.3, 5.6, 1.3 mg m−2 day−1, respectively. In Potsdam, total nitrate deposition to the WSS was greater than to the Nylasorb filter whereas in Solomons the opposite was true. This increased flux at Solomons may be because nitrate salts were formed on the surface of the Nylasorb filter by reaction of HNO3 with previously deposited sea salt aerosols. Average p-NO3− fluxes to the greased Mylar for the three sampling sites were 1.3, 1.3, and 1.0 mg m−2 day−1. The measured SO2 deposition velocity to the WSS in Potsdam and Solomons was 2.1 and 1.5 cm s−1, respectively, and agreed well with other studies. The deposition velocity for HNO3 to the WSS measured in Potsdam (8.1 cm s−1) was greater than to the Nylasorb filter (4.6 cm s−1) whereas in Solomons the opposite was true (4.6 cm s−1 vs. 7.1 cm s−1).