Barber Victoria P, LeMar Lexy N, Li Yaowei, Zheng Jonathan W, Keutsch Frank N, Kroll Jesse H
Department of Civil and Environmental Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Department of Chemical Engineering, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, United States.
Environ Sci Technol Lett. 2024 Aug 13;11(9):975-980. doi: 10.1021/acs.estlett.4c00473. eCollection 2024 Sep 10.
Organic alkoxy (RO) and peroxy (RO) radicals are key intermediates in multiphase atmospheric oxidation chemistry, though most of the study of their chemistry has focused on the gas phase. To better understand how radical chemistry may vary across different phases, we examine the chemistry of a model system, the 1-pentoxy radical, in three phases: the aqueous phase, the condensed organic phase, and the gas phase. In each phase, we generate the 1-pentoxy radical from the photolysis of -pentyl nitrite, run the chemistry under conditions in which RO radicals react with NO, and detect the products in real time using an ammonium chemical ionization mass spectrometer (NH CIMS). The condensed-phase chemistry shows an increase in formation of organic nitrate (RONO) from the downstream RO+NO reaction, which is attributed to potential collisional and solvent-cage stabilization of the RO-NO complex. We further observe an enhancement in the yield of carbonyl relative to hydroxy carbonyl products in the condensed phase, indicating changes to RO radical kinetics. The different branching ratios in the condensed phase impact the product volatility distribution as well as HO -NO chemistry, and may have implications for nitrate formation, aqueous aerosol formation, and radical cycling within atmospheric particles and droplets.
有机烷氧基（RO）和过氧自由基（RO₂）是多相大气氧化化学中的关键中间体，尽管对其化学性质的研究大多集中在气相。为了更好地理解自由基化学在不同相之间可能如何变化，我们研究了一个模型体系——1-戊氧基自由基在三个相中的化学性质：水相、凝聚有机相和气相。在每个相中，我们通过亚硝酸戊酯的光解产生1-戊氧基自由基，在RO自由基与NO反应的条件下进行化学反应，并使用铵化学电离质谱仪（NH₄⁺ CIMS）实时检测产物。凝聚相化学显示，下游RO + NO反应生成有机硝酸盐（RONO）的量增加，这归因于RO - NO络合物可能的碰撞和溶剂笼稳定作用。我们还进一步观察到，凝聚相中羰基产物相对于羟基羰基产物的产率有所提高，这表明RO自由基动力学发生了变化。凝聚相中不同的分支比会影响产物的挥发性分布以及HO₂ - NO₂化学性质，并可能对硝酸盐形成、水性气溶胶形成以及大气颗粒和液滴内的自由基循环产生影响。
