利用飞行时间质谱初步分析苯酚水相光化学反应的产物分布特征
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摘要
近年的实验室模拟和野外观测研究表明,酚类化合物的水相反应(aqueous-phase reaction)对环境二次有机气溶胶(secondary organic aerosol,SOA)的形成具有重要的贡献,因此探讨酚类化合物光化学过程中的演化特征有助于深化二次气溶胶形成的科学认识。本文以苯酚为研究对象,利用大气压喷雾电离(ESI)-飞行时间质谱(TOF-MS),对其在水相光化学反应下的产物分布特征进行了初步探讨。水相光照实验通过直接光解(无添加氧化剂)和光氧化反应(添加H_2O_2)两种情况进行。结果表明,两种方式进行的水相光化学反应均可能生成一系列的低聚物、羟基化化合物以及其他多官能团含氧产物。在m/z 150～400的区间内,添加H_2O_2的光氧化反应产物的分子式种类(150种)明显多于直接光解的形成产物(60种),但直接光解形成的高分子量产物(如低聚物等)离子丰度明显高于光氧化反应,直接光解的产物中可观察到四聚体化合物的生成;同时,水相光反应的产物在紫外-可见光波段内具有明显的光吸收增强特征。由此推断在大气中,以苯酚为代表的酚类化合物进入大气水相环境(云、雾水和气溶胶液态水)中发生的光化学过程对大气吸光性有机物或气溶胶的形成具有贡献作用。
Recent research regarding laboratory simulation and field observation indicates that the aqueous-phase reaction of phenols importantly contributed to the formation of ambient secondary organic aerosols(SOAs);therefore, the characterization of products formed from the photochemical evolution of phenols contributes to the understanding of the formation and chemical composition of SOAs. This study preliminarily investigated the distribution characteristics of products formed from the aqueous photochemical reaction of phenol by applying atmospheric pressure electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS). Here, the experiment was divided into two parts including direct photolysis(without an oxidant) and photo-oxidation(in the presence of H_2O_2). The results show that the photochemical reaction of phenol in the aqueous phase leads to the formation of diverse products including oligomers, hydroxylated compounds, and other polyfunctional oxygenated species. There were 150 molecular formulas observed in the products formed via photo-oxidation of phenol,higher than the case of products derived from the direct photolysis of phenol. However, the ion abundance of high molecular weight products(e.g., oligomers) was greater in the sample under direct photolysis than that under photo-oxidation. In particular, the tetramer was also found in the former. In addition, the light absorbance of the photochemical product exhibits a significant photo-enhancement in the ultraviolet and visible region. Our results suggest that the photochemical evolution of phenols dissolving into atmospheric waters(clouds, fog droplets, and aerosol liquid water) can contribute to the formation of atmospheric light-absorbing organic matter and aerosols.
Recent research regarding laboratory simulation and field observation indicates that the aqueous-phase reaction of phenols importantly contributed to the formation of ambient secondary organic aerosols(SOAs);therefore, the characterization of products formed from the photochemical evolution of phenols contributes to the understanding of the formation and chemical composition of SOAs. This study preliminarily investigated the distribution characteristics of products formed from the aqueous photochemical reaction of phenol by applying atmospheric pressure electrospray ionization time-of-flight mass spectrometry(ESI-TOF-MS). Here, the experiment was divided into two parts including direct photolysis(without an oxidant) and photo-oxidation(in the presence of H_2O_2). The results show that the photochemical reaction of phenol in the aqueous phase leads to the formation of diverse products including oligomers, hydroxylated compounds, and other polyfunctional oxygenated species. There were 150 molecular formulas observed in the products formed via photo-oxidation of phenol,higher than the case of products derived from the direct photolysis of phenol. However, the ion abundance of high molecular weight products(e.g., oligomers) was greater in the sample under direct photolysis than that under photo-oxidation. In particular, the tetramer was also found in the former. In addition, the light absorbance of the photochemical product exhibits a significant photo-enhancement in the ultraviolet and visible region. Our results suggest that the photochemical evolution of phenols dissolving into atmospheric waters(clouds, fog droplets, and aerosol liquid water) can contribute to the formation of atmospheric light-absorbing organic matter and aerosols.
引文
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[9]Smith J D,Sio V,Yu L,Zhang Q,Anastasio C.Secondary organic aerosol production from aqueous reactions of atmospheric phenols with an organic triplet excited state[J].Environ Sci Technol,2014,48(2):1049-1057.
[10]Yu L,Smith J,Laskin A,Anastasio C,Laskin J,Zhang Q.Chemical characterization of SOA formed from aqueousphase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical[J].Atmos Chem Phys,2014,14(24):13801-13816.
[11]Cappiello A,De Simoni E,Fiorucci C,Mangani F,Palma P,Trufelli H,Decesari S,Facchini M C,Fuzzi S.Molecular characterization of the water-soluble organic compounds in fogwater by ESIMS/MS[J].Environ Sci Technol,2003,37(7):1229-1240.
[12]Kourtchev I,Fuller S,Aalto J,Ruuskanen T M,McLeod M W,Maenhaut W,Jones R,Kulmala M,Kalberer M.Molecular composition of boreal forest aerosol from Hyytiala,Finland,using ultrahigh resolution mass spectrometry[J].Environ Sci Technol,2013,47(9):4069-4079.
[13]Laskin J,Laskin A,Nizkorodov S A.Mass spectrometry analysis in atmospheric chemistry[J].Anal Chem,2018,90(1):166-189.
[14]Zhao Y,Hallar A G,Mazzoleni L R.Atmospheric organic matter in clouds:Exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry[J].Atmos Chem Phys,2013,13(24):12343-12362.
[15]Lin P,Yu J Z,Engling G,Kalberer M.Organosulfates in humic-like substance fraction isolated from aerosols at seven locations in East Asia:A study by ultra-high-resolution mass spectrometry[J].Environ Sci Technol,2012,46(24):13118-13127.
[16]Sun Y L,Zhang Q,Anastasio C,Sun J.Insights into secondary organic aerosol formed via aqueous-phase reactions of phenolic compounds based on high resolution mass spectrometry[J].Atmos Chem Phys,2010,10(10):4809-4822.
[2]Nguyen T B,Lee P B,Updyke K M,Bones D L,Laskin J,Laskin A,Nizkorodov S A.Formation of nitrogen-and sulfurcontaining light-absorbing compounds accelerated by evaporation of water from secondary organic aerosols[J].J Geophys Res Atmos,2012,117:D01207.
[3]McNeill V F.Aqueous organic chemistry in the atmosphere:sources and chemical processing of organic aerosols[J].Environ Sci Technol,2015,49(3):1237-1244.
[4]Nguyen T B,Roach P J,Laskin J,Laskin A,Nizkorodov S A.Effect of humidity on the composition of isoprene photooxidation secondary organic aerosol[J].Atmos Chem Phys,2011,11(14):6931-6944.
[5]De Haan D O,Corrigan A L,Smith K W,Stroik D R,Turley JJ,Lee F E,Tolbert M A,Jimenez J L,Cordova K E,Ferrell GR.Secondary organic aerosol-forming reactions of glyoxal with amino acids[J].Environ Sci Technol,2009,43(8):2818-2824.
[6]De Haan D O,Hawkins L N,Kononenko J A,Turley J J,Corrigan A L,Tolbert M A,Jimenez J L.Formation of nitrogencontaining oligomers by methylglyoxal and amines in simulated evaporating cloud droplets[J].Environ Sci Technol,2011,45(3):984-991.
[7]Rogge W F,Hildemann L M,Mazurek M A,Cass G R,Simoneit R T.Sources of fine organic aerosol.9.Pine,oak and synthetic log combustion in residential fireplaces[J].Environ Sci Technol,1998,32(1):13-22.
[8]Yee L D,Kautzman K E,Loza C L,Schilling K A,Coggon MM,Chhabra P S,Chan M N,Chan A W H.Hersey S P,Crounse J D,Wennberg P O,Flagan R C,Seinfeld J H.Secondary organic aerosol formation from biomass burning intermediates:Phenol and methoxyphenols[J].Atmos Chem Phys,2013,13(16):8019-8043.
[9]Smith J D,Sio V,Yu L,Zhang Q,Anastasio C.Secondary organic aerosol production from aqueous reactions of atmospheric phenols with an organic triplet excited state[J].Environ Sci Technol,2014,48(2):1049-1057.
[10]Yu L,Smith J,Laskin A,Anastasio C,Laskin J,Zhang Q.Chemical characterization of SOA formed from aqueousphase reactions of phenols with the triplet excited state of carbonyl and hydroxyl radical[J].Atmos Chem Phys,2014,14(24):13801-13816.
[11]Cappiello A,De Simoni E,Fiorucci C,Mangani F,Palma P,Trufelli H,Decesari S,Facchini M C,Fuzzi S.Molecular characterization of the water-soluble organic compounds in fogwater by ESIMS/MS[J].Environ Sci Technol,2003,37(7):1229-1240.
[12]Kourtchev I,Fuller S,Aalto J,Ruuskanen T M,McLeod M W,Maenhaut W,Jones R,Kulmala M,Kalberer M.Molecular composition of boreal forest aerosol from Hyytiala,Finland,using ultrahigh resolution mass spectrometry[J].Environ Sci Technol,2013,47(9):4069-4079.
[13]Laskin J,Laskin A,Nizkorodov S A.Mass spectrometry analysis in atmospheric chemistry[J].Anal Chem,2018,90(1):166-189.
[14]Zhao Y,Hallar A G,Mazzoleni L R.Atmospheric organic matter in clouds:Exact masses and molecular formula identification using ultrahigh-resolution FT-ICR mass spectrometry[J].Atmos Chem Phys,2013,13(24):12343-12362.
[15]Lin P,Yu J Z,Engling G,Kalberer M.Organosulfates in humic-like substance fraction isolated from aerosols at seven locations in East Asia:A study by ultra-high-resolution mass spectrometry[J].Environ Sci Technol,2012,46(24):13118-13127.
[16]Sun Y L,Zhang Q,Anastasio C,Sun J.Insights into secondary organic aerosol formed via aqueous-phase reactions of phenolic compounds based on high resolution mass spectrometry[J].Atmos Chem Phys,2010,10(10):4809-4822.