Chilled-mirror hygrometers and capacitive relative humidity (RH) sensors are two of the most commonly used sensors for monitoring air vapor quantities in the atmosphere. Because of the increasing need for high fidelity climate data and the recent availability of new humidity sensors, there is a need for field comparison among various air humidity sensors including three different RH sensors (HMP45C, HMP233, and MP101) and two chilled-mirror hygrometers (DewTrack 200 and MET 2010). Potential microclimate effects on the RH sensors include ambient air temperature, air humidity, air pressure, ambient wind speed, and solar radiation. Results are applicable to guide the selection of air humidity monitoring in the U.S. Climate Reference Network (CRN) and to the analysis of air humidity data continuity and climate data adjustment modeling.