Mixture state of individual Asian dust particles at a coastal site of Qingdao, China

In order to investigate the characteristics of Asian dust particles before they leave the continent, particles were collected at a coastal site of Qingdao (120°27′E, 36°06′N) in northeastern China during three dust storm events in spring 2001. The elemental composition and size of individual dust particles, and their mixture state with sea salt, sulfate and nitrate were analyzed using electron microscopes and an energy dispersive spectrometer. It was found that far less than 10% of dust particles were internally mixed with sea salt. Although a number of dust particles contained Na, S, and Cl, the elements in most of the particles were more likely from crustal origins. The combination of reagent tests and elemental analysis revealed that 3.3–12.2% of dust particles contained sulfate and 6.5–10.0% contained nitrate on their surface. Number-size distributions of dust particles estimated from their electron microscope images had a distribution mode of around 3 μm diameter with the range of 1.0–8.0 μm. Out of this range, dust particles were rarely detected.