Kristensen K, Jensen L N, Glasius M, Bilde M
Department of Chemistry, Aarhus University, DK-8000 Aarhus C., Denmark.
Environ Sci Process Impacts. 2017 Oct 18;19(10):1220-1234. doi: 10.1039/c7em00231a.
This study presents a newly constructed temperature controlled cold-room smog chamber at Aarhus University, Denmark. The chamber is herein utilized to study the effect of sub-zero temperature on the formation and chemical composition of secondary organic aerosol (SOA) from ozone initiated oxidation of α-pinene. The chemical composition of α-pinene SOA formed from dark ozonolysis of α-pinene at 293 K and 258 K was investigated using High-Resolution Time-of-Flight Aerosol Mass Spectrometry (HR-ToF-AMS) and Ultra-High Performance Liquid Chromatography/Electrospray Ionization Quadrupole Time-of-Flight Mass Spectrometry (UHPLC/ESI-qToF-MS). For comparison, an OH-initiated oxidation experiment was performed at 293 K. In ozonolysis experiments it was found that oxygen-to-carbon (O : C) ratios were higher in the particles formed at 293 K compared to 258 K. A total of 16 different organic acids and 30 dimers esters were quantified in the collected particles composing up to 34% of the total α-pinene SOA mass with increased mass fraction of carboxylic acids in particles from α-pinene ozonolysis at 258 K compared to 293 K. In contrast, dimer esters showed suppressed formation at the sub-zero reaction temperature, thus contributing 3% to SOA mass at 258 K while contributing 9% at 293 K. SOA formed in the OH-initiated oxidation of α-pinene at 293 K resulted in low concentrations of dimer esters supporting Criegee intermediates as a possible pathway to dimer ester formation. Vapour pressure estimates of the identified carboxylic acids and dimer esters are presented and show how otherwise semi-volatile carboxylic acids at sufficiently low temperatures may classify as low or even extremely low volatile organic compounds (ELVOC), thus may add to an enhanced particle formation observed at the sub-zero temperature through gas-to-particle conversion. The change in chemical composition of the SOA particles with temperature is ascribed to a combination of effects: the decreased vapour pressures and hence increased condensation of carboxylic acids from the gas phase to the particle phase along with suppressed formation of the high molecular weight dimer esters and different gas and particle phase chemistry results in particles of different chemical composition as a consequence of low reaction temperatures.
本研究介绍了丹麦奥胡斯大学新建的一个温度可控的低温烟雾箱。该烟雾箱在此用于研究零下温度对α-蒎烯臭氧引发氧化形成的二次有机气溶胶（SOA）的形成及化学成分的影响。使用高分辨率飞行时间气溶胶质谱仪（HR-ToF-AMS）和超高效液相色谱/电喷雾电离四极杆飞行时间质谱仪（UHPLC/ESI-qToF-MS）研究了α-蒎烯在293 K和258 K下黑暗臭氧化形成的α-蒎烯SOA的化学成分。为作比较，在293 K下进行了OH引发的氧化实验。在臭氧化实验中发现，与258 K相比，293 K下形成的颗粒中氧碳比（O : C）更高。在所收集的颗粒中共定量了16种不同的有机酸和30种二聚体酯，它们占α-蒎烯SOA总质量的34%，与293 K相比，258 K下α-蒎烯臭氧化形成的颗粒中羧酸的质量分数增加。相比之下，二聚体酯在零下反应温度下形成受到抑制，因此在258 K时对SOA质量的贡献为3%，而在293 K时为9%。α-蒎烯在293 K下OH引发氧化形成的SOA导致二聚体酯浓度较低，这支持了Criegee中间体是二聚体酯形成的可能途径。给出了所鉴定的羧酸和二聚体酯的蒸气压估计值，并表明在足够低的温度下，原本半挥发性的羧酸如何可归类为低挥发性甚至极低挥发性有机化合物（ELVOC），从而可能通过气-粒转化增加在零下温度下观察到的颗粒形成增强。SOA颗粒的化学成分随温度的变化归因于多种效应的综合作用：蒸气压降低，因此羧酸从气相到颗粒相的冷凝增加，同时高分子量二聚体酯的形成受到抑制，以及不同的气相和颗粒相化学过程，导致由于反应温度低而形成化学成分不同的颗粒。
