Abstract. Cooking organic aerosol (COA) is one of the major constituents of particulate matter in urban areas. COA is oxidized by atmospheric oxidants such as ozone, changing its physical, chemical and toxicological properties. However, atmospheric chemical lifetimes of COA and its tracers such as oleic acid are typically longer than those that have been estimated by laboratory studies. We tackled the issue by considering temperature. Namely, we hypothesize that increased viscosity of COA at ambient temperature accounts for its prolonged atmospheric chemical lifetimes in wintertime. Laboratory-generated COA particles from cooking oil were exposed to ozone in an aerosol flow tube reactor for the temperature range of −20 to 35 °C. The pseudo-second-order chemical reaction rate constants (k2) were estimated from the experimental data by assuming a constant ozone concentration in the flow tube. The estimated values of k2 decreased by orders of magnitude for lower temperatures. The temperature dependence in k2 was fit well by considering the diffusion-limited chemical reaction mechanism. The result suggested that increased viscosity was likely the key factor to account for the decrease in chemical reactivity at the reduced temperature range, though the idea will still need to be verified by temperature-dependent viscosity data in the future. In combination with the observed global surface temperature, the atmospheric chemical lifetimes of COA were estimated to be much longer in wintertime (> 1 h) than in summertime (a few minutes) for temperate and boreal regions. Our present study demonstrates that the oxidation lifetimes of COA particles will need to be parameterized as a function of temperature in the future for estimating environmental impacts and fates of this category of particulate matter.

中文翻译：

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冬季条件下烹饪有机气溶胶颗粒的大气化学老化受到抑制

摘要。烹饪有机气溶胶（COA）是城市地区颗粒物的主要成分之一。 COA被臭氧等大气氧化剂氧化，改变其物理、化学和毒理学性质。然而，COA 及其示踪剂（如油酸）在大气中的化学寿命通常比实验室研究估计的要长。我们通过考虑温度来解决这个问题。也就是说，我们假设 COA 在环境温度下粘度增加是其冬季大气化学寿命延长的原因。将实验室从食用油中产生的 COA 颗粒暴露在气溶胶流管反应器中的臭氧中，温度范围为 -20 至 35 °C。假设流管中臭氧浓度恒定，根据实验数据估计准二级化学反应速率常数 (k2)。温度较低时，k2 的估计值会降低几个数量级。通过考虑扩散限制化学反应机制，k2 中的温度依赖性得到了很好的拟合。结果表明，粘度增加可能是导致温度范围降低时化学反应性降低的关键因素，尽管这一想法未来仍需要通过与温度相关的粘度数据来验证。结合观测到的全球表面温度，估计温带和寒带地区 COA 的大气化学寿命在冬季（> 1 小时）比夏季（几分钟）长得多。我们目前的研究表明，将来需要将 COA 颗粒的氧化寿命参数化为温度的函数，以估计此类颗粒物质的环境影响和命运。