Gaseous and particulate matter measurements were performed from January 1999 to December 2001 to assess seasonal and diurnal patterns of air pollutions in the Lanzhou Valley, China. The objectives are the determination of the temporal variability of total suspended particulate (TSP) matter and PM10 levels, and their relationship with the SO2 and NOx emissions and desert dust intrusions from the dust sources in the Hexi Corridor in Gansu Province. The results showed that concentrations of gaseous and particulate pollutants undergo seasonal variations characterized by a winter maximum levels for SO2 (0.094-0.208 mg/m3) and NO2 (0.068-0.089 mg/m3) and a spring maximum levels for TSP (0.885-1.037 mg/m3). Linear regression analysis indicated that the diurnal mean TSP/PM10 ratio may approximate to 3.0, and that the annual NO2/NOx ratio was approximately 0.86, with its highest monthly average of 0.91 in June and its lowest monthly average of 0.788 in January. The origin of PM10 episodes was investigated by correlating the PM10 episodes in the Lanzhou Valley with the high wind speeds in Jinchang (dust sources) in the Hexi Corridor, and also, by comparing the PM10 levels with the SO2 and NOx concentrations. Most of the 'high PM10 episodes' (1-h mean maximum >1.0 mg/m3) were attributed to the desert dust intrusions from the Hexi Corridor. The influence of the industrial and domestic emissions in the PM10 levels was evidenced during most of the periods with the PM10 levels less than 1.0 mg/m3.