How to find out / calculate the absolute humidity of the air entering the solar dryer at the point of adiabatic saturation (%) for finding out Pick-up Efficiency?

Reference 1. Fudholi, Ahmad, Kamaruzzaman Sopian, Mohammad H. Yazdi, Mohd Hafidz Ruslan, Mohamed Gabbasa, and Hussein A. Kazem. "Performance analysis of solar drying system for red chili." Solar Energy 99 (2014): 47-54.

Ref2. Banout, J., Ehl, P., Havlik, J., Lojka, B., Polesny, Z., & Verner, V. (2011). Design and performance evaluation of a Double-pass solar drier for drying of red chilli (Capsicum annum L.). Solar energy, 85(3), 506-515.