Atmospheric Environment 36 (2002) 3267–3276 Dry deposition measured with a water surface sampler: a comparison to modeled results Usama M. Shahin a , Thomas M. Holsen a , Mustafa Odabasi b, * a Department of Civil and Environmental Engineering, Clarkson University, Potsdam, NY 13699, USA b Department of Environmental Engineering, Faculty of Engineering, Dokuz Eylul University, Kaynaklar Campus, 35160 Buca, Izmir, Turkey Received 2 December 2001; accepted 24 April 2002 Abstract In this study, a water surface sampler (WSS) and a knife-leading-edge surrogate surface (KSS) covered with both a Nylasorb filter, and a greased strip were used to directly measure nitrate, sulfate, and ammonium dry fluxes in Chicago between May and October 1997. Concurrently, an annular denuder system was used to measure the ambient concentration of gaseous nitric acid, sulfur dioxide, and ammonia gases. Water evaporation and relative humidity were also simultaneously measured. The measured fluxes and ambient concentrations were used to calculate the mass transfer coefficients of all four species. The measured MTCs of water vapor, ammonia gas, nitric acid and sulfur dioxide were normalized to the square root of their diffusion coefficient and correlated to the wind speed at 10 m above the WSS. The best-fit model was k A ¼ D 0:5 A ½ð0:9870:1Þu 10 þð1:2670:3Þ; where k A is the air side mass transfer coefficient (cm s 1 ), D A is the air side diffusion coefficient (cm 2 s 1 ), u 10 is the wind speed 10 m above the WSS (m s 1 ), and the 7 is the 95% confidence interval. Field measured MTCs of water vapor, ammonia gas, nitric acid, and sulfur dioxide were used to examine the applicability of two models, the resistance model and the water evaporation model. Results showed that the resistance model predictions were statistically the same as the measured MTCs to the surrogate surfaces while the predictions of the water evaporation model was statistically smaller than the measured values. r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Dry deposition; Nitric acid; Ammonia; Water surface sampler; Mass transfer coefficient 1. Introduction Toxic pollutants are emitted to the atmosphere as a result of human activity where they mix, react with atmospheric constituents, are transported, and ulti- mately removed. The process by which these pollutants are transferred to terrestrial surfaces with no significant interaction with atmospheric moisture is termed dry deposition. A great deal of research has been conducted to investigate this process using a variety of approaches. These approaches include direct measurements using surrogate surfaces, micrometeorological, eddy accumu- lation, and gradient methods (Rattray and Sievering, 2001; Gallagher et al., 1997; Sutton et al., 1992; Bidleman, 1988). To date, there is no accepted technique that can be used universally to evaluate these ap- proaches. Direct measurements of dry deposition using surro- gate techniques are becoming increasingly popular (Yi et al., 1997a, 2001; Shahin et al., 1999, 2000; Odabasi *Corresponding author. Tel.: +90-232-453-1008; fax: +90- 232-453-0922. E-mail address: mustafa.odabasi@deu.edu.tr (M. Odabasi). 1352-2310/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S1352-2310(02)00315-1