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.

中文翻译：

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零以下温度对α-pine烯的臭氧分解作用对次级有机气溶胶形成和成分的影响

这项研究提出了丹麦奥尔胡斯大学新建的温度控制的冷室烟雾室。该腔室在本文中用于研究低于零温度对臭氧引发的α-pine烯氧化作用形成的次级有机气溶胶（SOA）的形成和化学成分的影响。使用高分辨率飞行时间气溶胶质谱法（HR-ToF-AMS）和超高效液相色谱法研究了293 K和258 K时α-pine烯的暗臭氧分解形成的α-pine烯SOA的化学成分/电喷雾电离四极杆飞行时间质谱（UHPLC / ESI-qToF-MS）。为了进行比较，在293 K上进行了OH引发的氧化实验。在臭氧分解实验中，发现氧与碳（O ：给出了鉴定出的羧酸和二聚酯的蒸气压估计值，并表明否则在足够低的温度下半挥发性羧酸如何分类为低或什至极低的挥发性有机化合物（ELVOC），因此可能增加观察到的颗粒形成通过气体到颗粒的转化在低于零的温度下 SOA颗粒的化学组成随温度的变化归因于以下综合作用：蒸汽压降低，因此羧酸从气相到颗粒相的缩合增加，同时高分子量二聚酯和由于低反应温度，不同的气相和粒子相化学反应会产生具有不同化学成分的粒子。