Turkish J. Eng. Env. Sci. 33 (2009) , 185 – 192. c  T ¨ UB ˙ ITAK doi:10.3906/muh-0905-19 An attempt to measure evaporation from a Class-A pan using naphthalene sublimation Kasım KOC ¸ AK * , Barı¸ sC ¸ ALDA ˘ G ˙ Istanbul Technical University, Department of Meteorology 34469 Maslak, ˙ Istanbul-TURKEY e-mail: kkocak@itu.edu.tr, caldagb@itu.edu.tr Received 15.05.2009 Abstract Determination of water losses via evaporation from a natural and man-made reservoir is of crucial importance for water budget calculations. However, the problem of evaporation measurement from free water surfaces has not been solved completely. In many applications, Class-A pans are generally used for measuring evaporation from free water surfaces. However, it is impossible to measure the evaporation by a Class-A pan when the air temperature is below freezing point. Therefore, Class-A pans must be removed from measurement stations during winter months. Under these considerations, we aimed to develop a new measurement method in order to overcome the disadvantages arising from measurements using a Class-A pan. For this reason, a relationship between mass losses due to naphthalene sublimation and evaporation from the free water surface has been investigated experimentally. In the experiment, evaporation from the Class-A pan and the sublimation from naphthalene block were measured using a hook-gauge and a precision balance, respectively. The Pearson correlation coefficient between these 2 mass losses is found to be 0.86, which is fairly encouraging for this first attempt. Key Words: Class-A pan, Evaporation, Naphthalene, Sublimation. Introduction In spite of the fact that there are several methods used in applications, the issue of determination of evaporation losses from free water surfaces is not resolved completely. The methods used in the application can be listed as water budget, energy budget, mass transfer, empirical formulas, and direct measurements. The water budget method does not give reliable results, especially for a short period of time. Moreover, the energy budget methods include many terms that require precise measurements. The mass transfer methods, which are based on Dalton’s law, give reasonably good results in many cases. Empirical formulas require careful application because of (a) difficulties in the measurement of variables at other places, (b) their limited range of accuracy in the model structure, and (c) difficulties in comparing one method with another due to method-specific model * Corresponding author 185