In situ measurements of interfacial phenomena with subatomic resolution under environmental disturbances have been a major goal of engineers and scientists engaged in the development of a microbalance sensor. Here, we demonstrate in situ measurements of the photooxidization process of alkanethiol self-assembled monolayers using dual-channel quartz-crystal microbalance (D-QCM) sensor that uses spherically contoured resonators to acoustically separate sensing channels for simultaneous compensation of environmental disturbances. Using a photolithographic method to make the D-QCM, the reference channel used in parallel with the sensing channel has almost the same resonant frequency and temperature coefficient of frequency. As a result, mass changes of 10-pg order accuracy were observed under ultraviolet radiation over four days.