By using the observational data obtained over the Bohai sea in Aug.-Sep., 2000, the variation characteristics of NOx, O3, SO2 and CO concentrations were firstly shown. The effects of solar radiation and weather conditions on the trace concentrations were analyzed. SO2 concentration was very stable, its' average value was about 0.006 mg.m-3. O3 concentration was mainly controlled by solar radiation. The concentration of CO and NOx was around 2.5-3.5 mg.m-3 and 0.1 mg.m-3, respectively, in weak weathers. Typhoon weather may made their concentrations increasing abruptly in a short time. The distinct differences of the pollutant concentrations between land and sea were also revealed, and the air quality over the Bohai sea in summer season was assessed based on the measurements.