Special issue  

With a wide variety of aerosol optical, physical, and chemical properties, China offers a test bed for the study of aerosol processes and techniques leading to a better understanding of aerosol properties. Aerosol concentrations in the southeast of China are periodically among the highest in the world, while at other times they are relatively low. The prevailing aerosol chemical composition (e.g., sulfate, nitrate, black carbon, brown carbon, particulate organic matter, sea salt) also changes significantly with the quick evolution of both the economy and society, along with the government’s strong environmental actions. The complex mechanisms of the secondary formation of aerosols and haze-fog interaction are still not well understood in this important region. In areas other than the southeast of China, topography determines the aerosol concentrations, which are consistently high. Examples are Sichuan Province or the Guanzhong Basin, i.e. large basins surrounded by high mountains. Furthermore, the large deserts in the west and north of China are strong sources of dust particles influencing the aerosol properties over a large part of the country. There are however also large areas with relatively low aerosol loading, in particular in mountainous areas and over the high plateaus such as Tibet. Aerosol chemical properties in the center and east of China still need to be clarified both geographically and temporally, e.g. distinguish spectrally absorbing components like mineral dust and brown carbon from remote sensing observations. Anthropogenic emissions of aerosols and precursor gases have a large influence on aerosol, in regards to both chemical and physical properties, and consequently optical properties, and their effects can be augmented by the transport of aerosol from elsewhere, such as carbonaceous particles from biomass burning aerosol and dust particles emitted from the deserts. The complex mechanisms and intrinsic relations of aerosol chemistry and physics, and their impacts on optical properties, need better interpretation based on comprehensive observation and analysis. Weather conditions have a large influence on the formation of haze, and haze episodes occur more and more frequently. The influence of large-scale weather systems such as the monsoon or the Siberian high may result in inter-annual variations in different regions of China. In particular the progress of the monsoon from south to north during spring and summer, and back in the autumn, results in strong variations in aerosol content.

In this special issue we focus on the application of remote sensing techniques using both ground-based and satellite measurements to study the temporal and spatial variations in aerosol properties over China on different scales. Results from campaigns in the Taklamakan Desert (Kashi), on the Tibetan Plateau, and other remote areas such as the NE of China are contrasted with those from densely populated and industrialized urban areas in the east of China. The special issue aims to bring together results from different projects such as Kashi, MOST, and regional air quality studies. Contributions are solicited on aerosol optical, physical, and chemical properties inferred from remote sensing observations and related optical techniques, and the spatial and temporal variations in these properties across China, with emphasis on processes leading to the observed differences, including the influence of meteorological conditions and large-scale weather systems.