Low bulk diffusivity inside viscous semisolid atmospheric secondary organic aerosol (SOA) can prolong equilibration time scale, but its broader impacts on aerosol growth and size distribution dynamics are poorly understood. Here, we present quantitative insights into the effects of bulk diffusivity on the growth and evaporation kinetics of SOA formed under dry conditions from photooxidation of isoprene in the presence of a bimodal aerosol consisting of Aitken (ammonium sulfate) and accumulation (isoprene or α-pinene SOA) mode particles. Aerosol composition measurements and evaporation kinetics indicate that isoprene SOA is composed of several semivolatile organic compounds (SVOCs), with some reversibly reacting to form oligomers. Model analysis shows that liquid-like bulk diffusivities can be used to fit the observed evaporation kinetics of accumulation mode particles but fail to explain the growth kinetics of bimodal aerosol by significantly under-predicting the evolution of the Aitken mode. In contrast, the semisolid scenario successfully reproduces both evaporation and growth kinetics, with the interpretation that hindered partitioning of SVOCs into large viscous particles effectively promotes the growth of smaller particles that have shorter diffusion time scales. This effect has important implications for the growth of atmospheric ultrafine particles to climatically active sizes.

中文翻译：

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粘性次生有机气溶胶的生长动力学和尺寸分布动力学

粘性半固体大气次级有机气溶胶（SOA）内部的低体积扩散系数可以延长平衡时间规模，但对气溶胶生长和尺寸分布动力学的更广泛影响尚不清楚。在这里，我们提出了定量的见解，涉及到在由Aitken（硫酸铵）组成的双峰气溶胶和积累（异戊二烯或α-pine烯）存在的双峰气溶胶存在下，干燥条件下异戊二烯的光氧化形成的SOA的扩散对SOA的生长和蒸发动力学的影响的定量见解。 SOA）模式粒子。气溶胶成分测量和蒸发动力学表明，异戊二烯SOA由几种半挥发性有机化合物（SVOC）组成，其中一些可逆地反应形成低聚物。模型分析表明，可以使用液体状的本体扩散率来拟合积累模式颗粒的蒸发动力学，但不能通过显着低估Aitken模式的演化来解释双峰气溶胶的生长动力学。相比之下，半固体场景成功地再现了蒸发和生长动力学，其解释是阻止SVOC划分为大的粘性颗粒有效地促进了具有较短扩散时间尺度的较小颗粒的生长。这种影响对大气超细颗粒生长至气候有效尺寸具有重要意义。半固体场景成功地再现了蒸发和生长动力学，其解释是阻止SVOCs分成大的粘性颗粒有效地促进了具有较短扩散时间尺度的较小颗粒的生长。这种影响对大气超细颗粒生长至气候有效尺寸具有重要意义。半固体场景成功地再现了蒸发和生长动力学，其解释是阻止SVOCs分成大的粘性颗粒有效地促进了具有较短扩散时间尺度的较小颗粒的生长。这种影响对大气超细颗粒生长至气候有效尺寸具有重要意义。