济南城区冬季PM2.5中硝基苯酚类化合物昼夜变化特征及生成机理
Formation mechanisms and diurnal variations of nitrophenols in PM2.5 during the winter in urban areas of Jinan
范晶 1刘晨 1苑金鹏 2张桂芹 3魏小锋 1王淑妍 1孙友敏1
作者信息
- 1. 山东建筑大学市政与环境工程学院,济南,250101
- 2. 齐鲁工业大学(山东省科学院)山东省分析测试中心,济南,250101
- 3. 山东建筑大学市政与环境工程学院,济南,250101;山东建筑大学资源与环境创新研究院,济南,250101
- 折叠
摘要
硝基苯酚类化合物(Nitrophenols,NPs)是细颗粒物中含氮有机物的重要组成部分,来自于污染源的一次排放或由前体物经过二次反应生成.采集了济南城区2021年12月17日—2022年1月19日冬季大气昼夜PM2.5样品,利用超高效液相色谱-质谱联用仪定量分析了样品中的7种硝基苯酚类化合物.结果表明,济南市区冬季大气PM2.5中ρ(ΣNPs)范围为13.22-72.42 ng·m-3,平均值为(45.56±13.22)ng·m-3.单个硝基苯酚类化合物中,4-硝基苯酚(4NP)占比最大,与国内其他城市监测结果一致.清洁天和污染天对比分析发现硝基苯酚类化合物在污染天的浓度更高,除4-硝基愈创木酚和5-硝基邻甲氧基苯酚外,其余硝基苯酚类化合物均是污染天浓度高.昼夜浓度对比发现ρ(∑NPs)在白天和夜间时段分别为(41.5±16.35)ng·m-3和(49.08±20.18)ng·m-3,大部分硝基苯酚类化合物的昼夜浓度呈现夜间浓度高于白天,但PM2.5污染加重时,白天时段的硝基苯酚类化合物浓度明显升高,甚至高于夜间浓度.利用量子化学高斯程序计算发现夜间硝基苯酚生成更容易,这跟晚上时段观测的硝基苯酚浓度高的现象相一致.当苯酚邻位和对位的取代基是给电子基团可以减小O—H解离焓,有利于苯氧自由基的生成.化学反应动力学给出了2-硝基苯酚(2NP)和4NP的生成路径,其反应活化能分别为49.6 kcal·mol-1和84.2 kcal·mol-1,生成速率常数分别为7.93×10-37 cm3·molecules-1·s-1和5.75×10-60 cm3·molecules-1·s-1,可知在清洁干燥天气的时候,硝基苯酚化合物的生成是非常困难的.但当有水分子和氨气等催化剂的协助后,2NP和4NP生成的活化能明显减小,其生成反应速率常数显著增大,说明重污染过程中,湿度增加和有氨气存在时会促进硝基苯酚的生成和积累.研究结果为城市氮氧化物削减和含氮有机物的二次生成提供一定的科学支撑.
Abstract
Nitrophenols(NPs)are an major group of nitrogen-containing compounds in fine particulates.NPs usually result from primary emissions by pollution sources and secondary reactions of some precursors.In this study,PM2.5 samples were collected diurnally from 17 December 2021 to 19 January 2022 in winter in urban areas of Jinan and seven NPs were detected using ultra high performance liquid chromatography-mass spectrometry(UHPLC-MS).ρ(∑NPs)in PM2.5 ranged from 13.22 ng·m-3 to 72.42 ng·m-3,and the average value was(45.56±13.22)ng·m-3.4-nitrophenol was the most abundant NP in Jinan,similar to the founding in other domestic cities.It was found thatρ(∑NPs)were much higher in polluted days than that in clean ones,except 2-methoxy-4-nitrophenol and 2-methoxy-5-nitrophenol.ρ(∑NPs)was(41.5±16.35)ng·m 3 and(49.08±20.18)ng·m3 during daytime and night,respectively,and the concentrations of major NPs were higher at night.As the concentration of PM2.5 increasing,ρ(∑NPs)rose significantly in daytime,sometimes even higher than that at night.Using Quantum Chemistry Gaussian program,calculations results showed that NPs were readily form at night,which was consistent with the observed data.Substituents in the orth-and para-positions of phenol were electron-donating groups reduce the value of bond dissociation energy(BDE)of O-H and benefit the formation of phenoxy radical.The activation energy of the formation of 2-nitrophenol(2NP)and 4-nitrophenol(4NP)were 49.6 kcal·mol-1 and 84.2 kcal·mol-1,respectively,and the reaction rate constant was 7.93×10-37 cm3·molecules-1·s-1 and 5.75× 10-60 cm3·molecules-1·s-1,respectively.Reaction process kenetic analysis was conducted to reveal the formation pathways for both chemicals.These results indicated that the formation of NPs was more difficult during clean and dry day.However,the activation barriers of 2NP and 4NP were obviously reduced and the rate constants were greatly increased as the existing of water molecule and ammonia.The results suggested that the increased humidity and ammonia of atmosphere in heavy pollution events could facilitate the formation and accumulation of NPs.The study would provide some scientific evident and theoretical support for urban NOX reduction and secondary production of nitrogenous organic matter.
关键词
硝基苯酚/超高效液相色谱-质谱联用仪/PM2.5/生成机制Key words
nitrophenols/ultra high performance liquid chromatography-mass spectrometry(UHPLC-MS)/PM2.5/formation mechanisms引用本文复制引用
基金项目
济南市高校创新团队项目(2020GXRC008)
济南市大气颗粒物来源解析研究项目(Z21001Z)
山东省自然基金(ZR2021QD146)
出版年
2024
NETL
NSTL
万方数据