Characterization of particulate matter and its extinction ability during different seasons and weather conditions in...

The Sinkiang Uygur Autonomous Region is located in western China and the centre of the Asian-European continent, which frequently suffers from sandstorm disasters and haze weathers. A 1-year measurement campaign in two selected points in Shihezi and Urumqi of Sinkiang was conducted to characterise the effects of particle matters and factors on particle extinction under different weather conditions. Results showed that the average concentration of PM_1-2.5 was 19.83, 9.230, 28.93 and 122.4 μg/m³ in Shihezi and 67.25, 16.80, 59.19 and 324.0 μg/m³ in Urumqi for spring, summer, autumn and winter, respectively. PM_5-10 concentrations can reach up to 500.0 and 160.0 μg/m³ during polluted weather conditions in Shihezi and Urumqi, respectively. PM_5-10 also accounted for the largest fraction in Shihezi and Urumqi for all types of weather, reaching up to 40.0% under dusty weather conditions. PM_1-2.5 significantly increased during winter possibly due to the increased demand for heating compared with non-heating periods. PM_0.5-1 is possibly produced from motor vehicle exhaust. Particle size is concluded to be the dominant factor for particle extinction capability under fine weather based on calculations of aerosol optical properties. The refractive index for a particle with a diameter of 100 μm (3.10-3.11i) is substantially larger than that with a diameter of 0.5000 μm (1.600-0.07000i), but the extinction capability of the latter is 1.30 times that of the former. Comparatively, when the mass concentration of coarse particles is over 17.0 times that of the fine particles, and then mass concentration becomes the dominant factor. Therefore, visibility is negatively correlated to particle mass variations during dust storms and hazy days but not for fine days.