Secondary aerosol (SA) frequently drives severe haze formation on the North China Plain. However, previous studies mostly focused on submicron SA formation, thus our understanding of SA formation on supermicron particles remains poor. In this study, PM_2.5 chemical composition and PM₁₀ number size distribution measurements revealed that the SA formation occurred in very distinct size ranges. In particular, SA formation on dust-dominated supermicron particles was surprisingly high and increased with relative humidity (RH). SA formed on supermicron aerosols reached comparable levels with that on submicron particles during evolutionary stages of haze episodes. These results suggested that dust particles served as a medium for rapid secondary organic and inorganic aerosol formation under favorable photochemical and RH conditions in a highly polluted environment. Further analysis indicated that SA formation pathways differed among distinct size ranges. Overall, our study highlights the importance of dust in SA formation during non-dust storm periods and the urgent need to perform size-resolved aerosol chemical and physical property measurements in future SA formation investigations that are extended to the coarse mode because the large amount of SA formed thereon might have significant impacts on ice nucleation, radiative forcing, and human health.

中文翻译：

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以粉尘为主的粗颗粒作为在高污染空气中快速形成二次有机和无机气溶胶的介质

二次气溶胶（SA）经常导致华北平原形成严重的霾。但是，以前的研究大多集中在亚微米级SA的形成上，因此，我们对在超微米级颗粒上形成SA的理解仍然很差。在这项研究中，PM _2.5的化学成分和PM ₁₀数尺寸分布测量表明，SA的形成发生在非常不同的尺寸范围内。特别是，在以尘埃为主的超微粒子上形成的SA令人惊讶地高，并且随着相对湿度（RH）的增加而增加。在薄雾发作的演变阶段，在超微米气溶胶上形成的SA达到了与在亚微米颗粒上相当的水平。这些结果表明，在高度污染的环境中，在有利的光化学和相对湿度条件下，粉尘颗粒可作为快速形成有机和无机气溶胶的媒介。进一步的分析表明，SA形成途径在不同的大小范围内有所不同。总体，