DOAS stands for "Differential Optical Absorption Spectroscopy", a method used to measure trace gases such as nitrogen dioxide, sulfur dioxide, and ozone in the atmosphere. There are various synonyms used for DOAS which are related to the process of measuring trace gases in the environment. Some of these synonyms include "gas monitoring", "spectroscopic gas analysis", "atmospheric gas analysis", and "trace gas detection". These terms describe the process of measuring and monitoring air quality in different environments such as industrial settings and urban areas. The use of DOAS and its related synonyms is crucial in understanding and mitigating the harmful effects of air pollution.