Predictions of diffusion rates of large organic molecules in secondary organic aerosols using the Stokes-Einstein and fractional Stokes-Einstein relations
Predictions of diffusion rates of large organic molecules in secondary organic aerosols using the Stokes-Einstein and fractional Stokes-Einstein relations
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DOI：
10.5194/acp-19-10073-2019
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发表时间：
2019-08-09
影响因子：
6.3
通讯作者：
Bertram, Allan K.
中科院分区：
文献类型：
--
作者：
Eyoy, Erin;Maclean, Adrian M.;Bertram, Allan K.
需要有关二次有机气溶胶 (SOA) 中有机分子扩散速率的信息，才能准确预测 SOA 对气候和空气质量的影响。扩散对于预测特定大气条件下 SOA 的生长、蒸发和反应速率非常重要。通常，研究人员使用粘度测量和斯托克斯-爱因斯坦关系（D 与 1/eta 成比例，其中 D 是扩散系数，eta 是粘度）来预测 SOA 内有机分子的扩散速率。然而，这种预测 SOA 中扩散的关系的准确性仍然不确定。使用光漂白后矩形区域荧光恢复 (rFRAP)，我们确定了 SOA 代理（包括柠檬酸、山梨醇和蔗糖柠檬酸混合物）中超过 8 个数量级的荧光有机分子的扩散系数。这些结果与文献数据相结合，评估了预测 SOA 中有机分子扩散的 Stokes-Einstein 关系。尽管几乎所有数据都与 Stokes-Einstein 关系在 10 倍范围内一致，但 xi = 0.93 的分数 Stokes-Einstein 关系（D 与 1/eta(xi) 成比例）是预测所研究的 SOA 代理中有机分子扩散的更好模型。此外，根据化学输运模型的输出，与 xi = 0.93 的分数斯托克斯-爱因斯坦关系相比，在大约 3 km 的高度上，斯托克斯-爱因斯坦关系可以高估 SOA 内有机分子的混合时间多达 1 个数量级。这些结果也对食品科学和生物分子保存等其他领域产生影响。
Information on the rate of diffusion of organic molecules within secondary organic aerosol (SOA) is needed to accurately predict the effects of SOA on climate and air quality. Diffusion can be important for predicting the growth, evaporation, and reaction rates of SOA under certain atmospheric conditions. Often, researchers have predicted diffusion rates of organic molecules within SOA using measurements of viscosity and the Stokes-Einstein relation (D proportional to 1/eta, where D is the diffusion coefficient and eta is viscosity). However, the accuracy of this relation for predicting diffusion in SOA remains uncertain. Using rectangular area fluorescence recovery after photobleaching (rFRAP), we determined diffusion coefficients of fluorescent organic molecules over 8 orders in magnitude in proxies of SOA including citric acid, sorbitol, and a sucrose-citric acid mixture. These results were combined with literature data to evaluate the Stokes-Einstein relation for predicting the diffusion of organic molecules in SOA. Although almost all the data agree with the Stokes-Einstein relation within a factor of 10, a fractional Stokes-Einstein relation (D proportional to 1/eta(xi)) with xi = 0.93 is a better model for predicting the diffusion of organic molecules in the SOA proxies studied. In addition, based on the output from a chemical transport model, the Stokes-Einstein relation can overpredict mixing times of organic molecules within SOA by as much as 1 order of magnitude at an altitude of similar to 3 km compared to the fractional Stokes-Einstein relation with xi = 0.93. These results also have implications for other areas such as in food sciences and the preservation of biomolecules.