修复工作包括除去500年来落在上面的尘埃以及前人为修复壁画而遮住原作的笔触。
The restoration removed 500 years of dirt while also removing previous restoration works that masked Leonardo's own work.
这些大气粒子或浮质可能是自然形成的，也可能是人为产生的，它们包括富含矿物质的尘埃、煤烟、有机分子以及海盐晶体。
These atmospheric particles or aerosols maybe natural formed or caused by the human actions. They consist of dust, soot, organic molecules, as well as sea salt crystals which are mineral-rich.
地球上的大气自然的受到沙尘暴和火山喷发的尘埃和气体的污染。但是最严重的空气污染确实人为的。
The earth's atmosphere is polluted naturally by sandstorms and the dust and gases from volcanoes. but the most serious kind of air pollution comes from people.
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