To predict important secondary organic aerosol (SOA) properties, information on viscosity or diffusion rates within SOA is needed. Ozonolysis of β-caryophyllene is an important SOA source; however, very few viscosity or diffusion rate measurements have been performed for this SOA type and none as a function of relative humidity (RH). In this study, we measured viscosity as a function of RH for SOA generated from the ozonolysis of β-caryophyllene using the poke-flow technique. At an RH of 0 and 48%, the viscosity was between 6.9 × 10⁵ and 2.4 × 10⁷ Pa s, and between 1.3 × 10³ and 5.6 × 10⁴ Pa s, respectively. Based on these viscosities and the fractional Stokes–Einstein equation, characteristic mixing timescales of organics within 200 nm β-caryophyllene SOA particles range from ∼0.2 h at 0% RH to <3 s at 48% RH, suggesting that these particles should be well-mixed under most conditions in the lower atmosphere. The chemical composition of the SOA was also determined using nano-desorption electrospray ionization mass spectrometry. The measured chemical composition and the method of DeRieux et al. (ACP, 2018) were used to predict the viscosity of β-caryophyllene SOA. If the mass spectra peak abundances were adjusted to account for the sensitivity of the electrospray ionization to larger molecular weight components, the predicted viscosity overlapped with the measured viscosity at 0% RH, while the predicted viscosities at 15–48% RH were slightly higher than the measured viscosities. The measured viscosities also overlapped with viscosity predictions based on a simple mole-fraction based Arrhenius mixing rule.

中文翻译：

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β-石竹烯臭氧分解过程产生的次级有机气溶胶的湿度依赖性粘度：测量，预测和意义

为了预测重要的次要有机气溶胶（SOA）特性，需要有关SOA内粘度或扩散速率的信息。β-石竹烯的臭氧分解是重要的SOA来源。但是，对于这种SOA类型，很少进行粘度或扩散速率测量，而没有作为相对湿度（RH）的函数进行测量。在这项研究中，我们使用oke流技术测量了β-石竹烯臭氧分解产生的SOA的粘度与RH的关系。在RH为0和48％时，粘度在6.9×10 ⁵和2.4×10 ⁷ Pa s之间，在1.3×10 ³和5.6×10 ^4之间。Pa s。根据这些粘度和分数斯托克斯-爱因斯坦方程，在200 nmβ-石竹烯SOA颗粒内有机物的特征混合时间范围从0％RH时约0.2 h到48％RH时<3 s，这表明这些颗粒应该很好在大多数条件下，在较低的大气中混合。还使用纳米解吸电喷雾电离质谱法确定了SOA的化学成分。测得的化学成分和DeRieux等的方法。（ACP，2018）用来预测β-石竹烯SOA的粘度。如果调整质谱图的峰丰度以考虑电喷雾电离对较大分子量组分的敏感性，则在0％RH时，预测粘度与测得的粘度重叠，而在15-48％RH时，预测粘度略高于测得的粘度。测得的粘度也与基于简单摩尔分数的Arrhenius混合规则的粘度预测相重叠。