Investigation on organic particles was limited in the background regions of Yangtze River Delta (YRD) and little information has been obtained on organic particles of Lin’an (LA). In the present study, the morphology, composition, mixing state, and size of organic aerosols with diameter less than 1 µm were characterized at Lin’an from 20 March 2019 to 20 April 2019. In all samples, irregular types of organic matter (OM) particles were high fraction during morning (72.4%), afternoon (59.1%), and evening (52%), and most of them were internally mixed. In our study, we identified a higher fraction of internally mixed particles in evenings (85%), followed by afternoon (81%), and fewer mixed particles in mornings (68%), indicating particle growth during afternoon and evening. Further, the results show that fraction of organic coating particles was higher in evening (27.4%) and afternoon (12%) indicates strong photochemical processes and formation of secondary organic aerosol on the inorganic particles and new particles formation. Our study reveals that biomass burning in the morning and coal burning from heavy industries, power plants, and vehicles in surrounding urban regions in the afternoon and evenings significantly affected background air quality.

对长江三角洲 (YRD) 背景区域有机颗粒物的调查有限，而关于临安 (LA) 有机颗粒物的信息也很少。在本研究中，于 2019 年 3 月 20 日至 2019 年 4 月 20 日在临安对直径小于 1 µm 的有机气溶胶的形态、组成、混合状态和大小进行了表征。在所有样本中，不规则类型的有机物（OM ) 颗粒在早上 (72.4%)、下午 (59.1%) 和晚上 (52%) 的比例较高，并且大部分是内部混合的。在我们的研究中，我们发现晚上的内部混合颗粒比例较高 (85%)，其次是下午 (81%)，早上的混合颗粒较少 (68%)，这表明颗粒在下午和晚上生长。进一步，结果表明，有机涂层颗粒的比例在晚上 (27.4%) 和下午 (12%) 较高，表明强烈的光化学过程和二次有机气溶胶在无机颗粒上的形成和新颗粒的形成。我们的研究表明，上午燃烧生物质以及下午和晚上周边城市地区的重工业、发电厂和车辆燃烧的煤炭显着影响背景空气质量。