School of Marine and Atmospheric Sciences, Stony Brook University, Stony Brook, New York 11794, United States.
Environ Sci Technol. 2021 Jun 1;55(11):7266-7275. doi: 10.1021/acs.est.0c07668. Epub 2021 May 11.
Organic aerosol (OA) is ubiquitous in the atmosphere and, during transport, can experience chemical transformation with consequences for air quality and climate. Prediction of the chemical evolution of OA depends on its reactivity with atmospheric oxidants such as the OH radical. OA particles undergo amorphous phase transitions from liquid to solid (glassy) states in response to temperature changes, which, in turn, will impact its reactivity toward OH oxidation. To improve the predictability of OA reactivity toward OH oxidation, the reactive uptake coefficients (γ) of OH radicals reacting with triacontane and squalane serving as amorphous OA surrogates were measured at temperatures from 213-293 K. γ increases strongest with temperature when the organic species is in the liquid phase, compared to when being in the semisolid or solid phase. The resistor model is applied, accounting for the amorphous phase state changes using the organic species' glass transition temperature and fragility, to evaluate the physicochemical parameters of the temperature dependent OH uptake process. This allows for the derivation of a semiempirical formula, applicable to models, to predict the degree of oxidation and chemical lifetime of the condensed-phase organic species for typical tropospheric temperature and humidity when OA particle viscosity is known.
有机气溶胶 (OA) 在大气中无处不在，在传输过程中会经历化学转化，从而对空气质量和气候产生影响。OA 化学演化的预测取决于其与大气氧化剂（如 OH 自由基）的反应性。OA 颗粒会在温度变化下从液态向无定形固态（玻璃态）转变，从而影响其对 OH 氧化的反应性。为了提高 OA 对 OH 氧化反应性的可预测性，测量了作为无定形 OA 替代物的三癸烷和角鲨烷与 OH 自由基反应的反应性吸收系数 (γ)，温度范围为 213-293 K。与处于半固态或固态相比，当有机物质处于液态时，γ 随温度的升高而增强。应用电阻器模型，利用有机物质的玻璃化转变温度和脆性来考虑无定形相态变化，评估与温度相关的 OH 吸收过程的物理化学参数。这允许推导出一个半经验公式，适用于模型，以预测当 OA 颗粒粘度已知时，典型的对流层温度和湿度下凝聚相有机物质的氧化程度和化学寿命。
