低NO_(x)环境异戊二烯促进甲苯生成甲基丁烯二醛的模拟实验

A chamber study on isoprene-promoting the production of toluene-derived methylbutenedial in low NO_(x) environment

在低NO_(x)浓度条件下开展甲苯和异戊二烯复合体系的烟雾箱模拟实验,使用高时间分辨率的在线质子转移反应飞行时间质谱(PTR-TOF-MS)实时监测混合体系中反应物与产物的浓度变化情况,探究人为源与天然源交汇过程中,自然源挥发性有机物(BVOCs)对人为挥发性有机物(AVOCs)化学降解的影响.结果表明,异戊二烯与甲苯竞争OH自由基,从而抑制了甲苯的化学降解,该竞争反应开始得越早,抑制效果越显著.研究还发现异戊二烯会增强甲苯RO_(2)降解途径产物的产量,生成更多1,4不饱和-二羰基化合物(如丁烯二醛和甲基丁烯二醛)与二羰基化合物(如乙二醛和甲基乙二醛),其中甲基丁烯二醛增量最高可达38.6%.此外,异戊二烯快速氧化生成的RO_(2)自由基碳数更少,可能与甲苯氧化生成的RO_(2)自由基发生了快速的交叉反应,有利于甲苯RO自由基的生成及裂解,最终导致甲苯RO_(2)途径裂解产物的增加.

Toluene and isoprene are typical anthropogenic volatile organic compounds(AVOCs)and biological volatile organic compounds(BVOCs),respectively.In this study,smog chamber experiments were carried out to simulate photochemical reactions of toluene and isoprene at low NOx levels.In order to investigate the effect of BVOCs on the chemical degradation of AVOCs during the interaction between anthropogenic and biogenic emissions,a proton-transfer-reaction time-of-flight mass spectrometry(PTR-TOF-MS)was used to monitor the real-time concentration variations of the key gaseous substances in the mixed system.The results show that isoprene inhibited the chemical degradation of toluene,which might be related to the competitive reactions with OH radicals between isoprene and toluene.Moreover,the earlier competitive reaction began,the more significant the inhibition effect was.And isoprene enhanced the production of toluene RO_(2) degradation pathway products,resulting in more unsaturated 1,4-dicarbonyl compounds(Butenedial,Methyl-butenedial)and dicarbonyl compounds(Glyoxal,Methylglyoxal).The increment in methylbutenedial was up to 38.6%.Also,the RO_(2)•generated by the rapid oxidation of isoprene had less carbon number,which may have a rapid cross-reaction with the RO_(2)•generated by toluene oxidation.The cross reaction was conducive to the generation and cleavage of toluene RO•and ultimately led to an increase of the products from toluene RO_(2)•channel.This study can improve an understanding of the impact of BVOCs on AVOCs degradation during the interaction process between anthropogenic and biogenic emissions,and provide insights into regional air pollution prevention and control in the future.