The atmospheric reactions of secondary organic material (SOM) with gaseous reactants alter its composition and properties, which can further impact the Earth system. To investigate how water content and precursor affect the reactivity of SOM, the reaction between toluene-derived SOM and ammonia for variable relative humidity (RH) was investigated. A Fourier transform infrared spectrometer was used to monitor the absorbance change of the functional groups as a function of exposure time. There was a fast response to water vapor compared with a gradual spectral variation associated with ammonia uptake. When RH is higher than 25 ± 5%, the spectral changes across 1500–1900 cm^–1 showed a decreasing trend for carboxylic acids and an increasing trend for carboxylates, suggesting a neutralization reaction by ammonia uptake. The observed increasing trend for the region of 1270–1360 cm^–1 might be associated with amines and suggests the formation of organonitrogen compounds for the toluene-derived SOM aging by ammonia at high RH. The corresponding intensity change of C–O groups (1000–1260 cm^–1) with the increased liquid water content as RH increases at the first 6 min suggested that the possible chemical reactions, such as hydrolysis of acetals and hemiacetals to aldehydes and alcohols or esters to carboxylic acids and alcohols, might change the diffusivity of particles and affect the ammonia uptake. The threshold point of ammonia uptake at 30% RH was consistent with a more significant absorbance change of liquid water content and C–O groups at RH ≥ 35 ± 5%. For comparison between anthropogenic and biogenic precursor gases, an isoprene-derived SOM film was also studied. It was more volatile and reactive to ammonia than the toluene-derived SOM. This result implies that the diffusion of ammonia was faster inside isoprene-derived SOM. Overall, the chemical reactions of SOM particles during their atmospheric residence time are precursor- and RH-dependent, which may alter the current understanding of their impact on the Earth system.

中文翻译：

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甲苯衍生的次要有机材料与氨的反应性和水蒸气的影响

次级有机材料（SOM）与气态反应物在大气中的反应会改变其组成和性质，从而可能进一步影响地球系统。为了研究水分和前体物如何影响SOM的反应性，研究了甲苯衍生的SOM与氨在可变相对湿度（RH）下的反应。使用傅立叶变换红外光谱仪监测官能团的吸光度变化与曝光时间的关系。与氨吸收相关的逐渐光谱变化相比，对水蒸气的响应迅速。当RH高于25±5％时，光谱在1500–1900 cm ^{–1范围内}变化羧酸显示出下降的趋势，而羧酸盐显示出上升的趋势，表明通过氨的吸收进行中和反应。观察到的在1270–1360 cm ^–1区域的增长趋势可能与胺有关，并表明在高RH下氨引起的甲苯衍生的SOM老化过程中会形成有机氮化合物。C–O组的相应强度变化（1000–1260 cm ^–1）在最初6分钟内随着RH的增加而增加的液态水含量表明，可能的化学反应（例如乙缩醛和半缩醛水解为醛和醇或酯水解为羧酸和醇）可能会改变颗粒的扩散性并影响氨吸收。在RH≥35±5％的条件下，相对湿度30％时氨的吸收阈值与液态水含量和C–O组的吸光度变化更为显着。为了比较人为和生物前体气体，还研究了异戊二烯衍生的SOM膜。它比甲苯衍生的SOM更易挥发，对氨更具反应性。该结果暗示氨的扩散在异戊二烯衍生的SOM内更快。全面的，