Experiments for estimation of SO emissions from one point-source and one area-source in Shijingshan District, Beijing were introduced, in which a mobile mini-DOAS system was employed to study the environmental prerequisites for its application. A comparison among meteorological conditions for each experiment indicates that, (1) a mid-scale weather system was necessary for measurement so as to avoid local mountain-valley winds; (2) when mixing height and wind velocity were low, more accurate measurements can be obtained and are closer to statistical values from the local authority; (3) using wind direction and velocity at emission height yielded a better estimation of pollutant emission of the point source.