Abstract
The unique geographical location of the Tibetan Plateau (TP) plays an important role in regulating global climate change, but the impacts of the chemical components and atmospheric processing on the size distribution and mixing state of individual particles are rarely explored in the southeastern margin of the TP, which is a transport channel for pollutants from Southeast Asia during the pre-monsoon season. Thus a single-particle aerosol mass spectrometer (SPAMS) was deployed to investigate how the local emissions of chemical composition interact with the transporting particles and assess the mixing state of different particle types and secondary formation in this study. The TP particles were classified into six main types: the rich-potassium (rich-K) type was the largest fraction of the total particles (30.9 %), followed by the biomass burning (BB) type (18.7 %). Most particle types were mainly transported from the surroundings and cross-border of northern Myanmar; but the air masses from northeastern India and Myanmar show a greater impact on the number fraction of BB (31.7 %) and Dust (18.2 %) types, respectively. Besides, the two episodes events with high particle concentrations showed that the differences in the meteorological conditions in the same air clusters could cause significant changes in chemical components, especially the Dust and EC-aged types changed by a sum of 93.6 % and 72.0 % respectively. Ammonium and Dust particles distribute at a relatively larger size (~ 600 nm), but the size peak of other types is present at ~ 440 nm. The easily volatilized nitrate (62NO3−) during the transport process leads the more abundant sulfate (97HSO4−) to mix internally with the TP particles. C2H3O+, HC2O4−, NH4+, NO3−, and HSO4−, severed as the indicators of secondary formation, are present in the atmospheric aging process of photo-oxidation and aqueous reaction by a linear correlation with Ox (O3+NO2) and relative humidity (RH). This study provides insights that can improve the knowledge of particle composition and size, mixing state, and aging mechanism at high time resolution over the TP region.
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