Tracing the evolution of morphology and mixing state of soot particles along with the movement of an Asian dust storm
Abstract. Tracing the aging progress of soot particles during transport is highly challenging. An Asian dust event could provide an ideal opportunity to trace the continuous aging progress of long-range transported soot particles. Here, we collected individual aerosol particles at an inland urban site (T1) and a coastal urban site (T2) in China and a coastal site (T3) in southwestern Japan during an Asian dust event. Microscopic analysis showed that the number fraction of soot-bearing particles
... t-bearing particles increased from 19 % to 22 % from T1 to T2 in China but surprisingly increased to 56 % at T3 in Japan. The dominant fresh soot (71 %) at T1 became partially embedded (70 %) at T2 and fully embedded (84 %) at T3. These results indicated that the soot particles had lower deposition than other aerosol types and became more aged from T1 to T3. The fractal dimension of the soot particles slightly changed from 1.74 at T1 and 1.78 at T2 but significantly became 1.91 at T3. We found that the soot morphology compressed depending on secondary coating thickness and relative humidity. Moreover, we observed a unique mixing structure at T3 that tiny soot particles were seemly broken from large ones cross the East China Sea and distributed in organic coatings instead of sulfate core in particles. Our study provide important constraints of the morphological effects to better understand changes of microscopic structures of soot. These new findings will be helpful to improve optical calculation and modeling of soot particles and their regional climate effects in the atmosphere.