Appearance of strong absorbers and fluorophores in limonene-O3 secondary organic aerosol due to NH4+-mediated chemical aging over long time scales
Appearance of strong absorbers and fluorophores in limonene-O3 secondary organic aerosol due to NH4+-mediated chemical aging over long time scales
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DOI：
10.1029/2009jd012864
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发表时间：
2010-03-06
影响因子：
4.4
通讯作者：
Nizkorodov, Sergey A.
中科院分区：
文献类型：
--
作者：
Bones, David L.;Henricksen, Dana K.;Nizkorodov, Sergey A.
本研究研究了由萜类的臭氧分解制备的模型生物二次有机气溶胶(SOA)的长期化学老化。采用电喷雾电离质谱仪(ESI-MS)、紫外-可见光谱、傅立叶变换红外光谱(FTIR)、核磁共振和三维荧光等技术，研究了作用于底物和浸提液中的有机硅化学成分的变化。将氨离子或氨基酸添加到柠檬烯SOA中，可重复产生橙色物种，这些物种强烈吸收可见光辐射，并在UV和可见光波长下发光。同时向SOA水提液中加入H2SO4抑制了这种颜色变化。这些观察表明，老化过程的存在导致了含有有机氮的严重共轭分子。通过吸收光谱和荧光光谱对添加的氨基酸的依赖关系，证实了发色团中氮的存在。与吸收光谱和荧光光谱的强烈变化相反，ESI-MS、FTIR和核磁共振光谱没有明显变化，表明发色团在老化的SOA中是次要物种。陈化柠檬烯+NH_4+SO_4的水提物在500 nm波长处的有效基-e吸收系数与3 L g(-1)cm(-1)相近。假设受污染的农村空气的典型颗粒物浓度给出的气溶胶吸收系数上限为0.2Mm(-1)，这是由于陈年的柠檬烯氧化产物造成的。因此，如果在含有NH4+的气溶胶存在的情况下经历老化，生物来源的SOA可能会变得吸收能力较弱。
This study investigated long-term chemical aging of model biogenic secondary organic aerosol (SOA) prepared from the ozonolysis of terpenes. Techniques including electrospray ionization mass spectrometry (ESI-MS), UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, NMR, and three-dimensional fluorescence were used to probe the changes in chemical composition of SOA collected by impaction on substrates and also of aqueous extracts of SOA. The addition of ammonium ions or amino acids to limonene SOA reproducibly produced orange-colored species that strongly absorbed visible radiation and fluoresced at UV and visible wavelengths. Simultaneous addition of H2SO4 to the SOA aqueous extracts inhibited this color transformation. These observations suggest the existence of aging processes leading to heavily conjugated molecules containing organic nitrogen. The presence of nitrogen in the chromophores was confirmed by the dependence of the absorption and fluorescence spectra on the amino acids added. In contrast to the strong change in the absorption and fluorescence spectra, there was no significant change in the ESI-MS, FTIR, and NMR spectra, suggesting that the chromophores were minor species in the aged SOA. Aqueous extracts of aged limonene + NH4+ SOA were characterized by an effective base-e absorption coefficient of similar to 3 L g(-1) cm(-1) at 500 nm. Assuming particulate matter concentrations typical of polluted rural air gives an upper limit of 0.2 M m(-1) for the aerosol absorption coefficient due to the aged limonene oxidation products. Biogenic SOA can therefore become weakly absorbing if they undergo aging in the presence of NH4+-containing aerosol.