Although LanTAaou is one of the most heavily polluted cities in China, the composition of its air pollutants have not yet been studied in detail. The data of four months on the concentrations and compositions of ions from daily air-filter samples in the winter and spring during 2007-2008 were analyzed to investigate temporal trends and their possible causes. The results indicate that mean concentrations of almost all the aerosol components are greater in winter than in spring due to stronger emissions in winter and weaker localized dispersion. Spring dust storms are the major cause of the highest peak PM10 concentrations recorded during the study period; however, these elevated levels were transient. Ion concentrations related to coal combustion show the greatest reduction from winter to spring, while the concentrations of strong crustal components show a less-pronounced reduction. Strong cycles in the levels of particulate matter （PM） and all ions are also observed during the winter months due to meteorological conditions. Depending on the season, nine different ions accounted for 20%-50% of the PM concentration. The particle size of polluting ions was constant at times of increasing PM concentrations （particularly during winter）, whereas the particle size of crustal ions in- creased dramatically during spring dust storms. Local meteorological conditions （especially wind speed） have a strong influence on the levels of pollutants. Four dust storms were noted, including one during winter. In summary, the regional transport of desert dust from the Gobi can significantly affect air quality and the chemical composition of aerosols in Lanzhou. The dust storms can strongly increase concentration of crustal ions, which are characteristics of deserts in northwestern China. This observation is in agreement with back-trajectories, which show reduced levels of pollutant ions during dust storms. Data on nitrate：sulfate ratios indicate that stationary point sources are the main source of ions rather than mobile
Feng She YiFan Cheng ShiGong Wang YongTao Guo JinYan Wang MinJing Ma KeZheng Shang
A severe dust event occurred from April 23 to April 27, 2014, in East Asia. A state-of-the-art online atmospheric chemistry model, WRF/Chem, was combined with a dust model, GOCART, to better understand the entire process of this event. The natural color images and aerosol optical depth （AOD） over the dust source region are derived from datasets of moderate resolution imaging spectroradiometer （MODIS） loaded on a NASA Aqua satellite to trace the dust variation and to verify the model results. Several meteorological conditions, such as pressure, temperature, wind vectors and relative humidity, are used to analyze meteorological dynamic. The results suggest that the dust emission occurred only on April 23 and 24, although this event lasted for 5 days. The Gobi Desert was the main source for this event, and the Taklamakan Desert played no important role. This study also suggested that the landform of the source region could remarkably interfere with a dust event. The Tarim Basin has a topographical effect as a ＂dust reservoir＂ and can store unsettled dust, which can be released again as a second source, making a dust event longer and heavier.
