WALL-E/Vocus AIM data: Online particle phase chemical composition

The spontaneous formation of OH radicals at the air-water interfaces of
organic droplets was invstigated. In our study, we performed on line
particle phase size resolved measurements, aiming to understand whether or
not the oxidation process depends on the size of the particles. The on
line measurements were performed using the WALL-E (wall free particle
evaporator) particle phase inlet coupled with a Vocus AIM (adduct
ionization mechanism) high resolution mass spectrometer. For the
experiments of this study, iodide (I – ) was selected as the reagent ion,
as it is suitable for the detection of carboxylic acids. We
monitored the signal of the studied organic compounds (reactants) i.e.,
citric, maleic and aconitic acid as a function of particle size, as well
as the signals of the generated products.As final oxidation products we
identified a) Citric acid + OH: malonic, malic, hydroxy maleic and
oxyglutaric acids, and C5H6O6, b) Maleic acid + OH: malic and acrylic
acids and c) Aconitic acid + OH: malonic, malic, hydroxy maleic and
oxyglutaric acids, and C4H4O6. The product yield was determined by
dividing the product signal by the reactant signal. These results are only
qualitative. Our size resolved online measurements revealed that the
product yield formation is increasing as a function of the
surface-to-volume ratio, meaning that the oxidation is promoted at smaller
particles. This observation is in excellent agreement with the offline
measurements described in the main text of the manuscript.  The
data given here contain all the raw signals of the above mentioned
compounds as a function of sampling time (in minutes), i.e., time series.
We also give the signals of water and iodine (reagent ion), with which we
normalised the signals of the organics. Finally, we demonstrate some
control experiments that we performed regarding the potential fragments of
the parent compounds in the Wall-E source.

研究了有机液滴气-水界面处羟基自由基（OH radicals）的自发形成过程。本研究中，我们开展了在线粒径分辨的颗粒相测量，旨在探究氧化过程是否依赖于颗粒尺寸。在线测量采用WALL-E（无壁颗粒蒸发器，wall free particle evaporator）颗粒相进样口与Vocus AIM（加合物电离机制，adduct ionization mechanism）高分辨质谱仪联用的装置进行。实验中选择碘离子（I⁻）作为反应离子，因其适用于羧酸的检测。我们监测了目标有机化合物（反应物，即柠檬酸、马来酸和乌头酸）的信号随颗粒尺寸的变化，同时也监测了生成产物的信号。鉴定出的最终氧化产物包括：a) 柠檬酸+OH：丙二酸、苹果酸、羟基马来酸、氧戊二酸及C5H6O6；b) 马来酸+OH：苹果酸和丙烯酸；c) 乌头酸+OH：丙二酸、苹果酸、羟基马来酸、氧戊二酸及C4H4O6。产物产率通过产物信号与反应物信号的比值计算得出，结果仅为定性分析。粒径分辨在线测量表明，产物产率随颗粒表面体积比的增大而增加，即较小颗粒更易发生氧化反应。该观察结果与手稿正文所述的离线测量结果高度一致。本数据集包含上述所有化合物的原始信号随采样时间（单位：分钟）变化的时间序列数据，同时提供了水和碘（反应离子）的信号——我们利用这些信号对有机化合物的信号进行了归一化处理。此外，数据集还展示了针对WALL-E源中母体化合物潜在碎片开展的若干对照实验数据。