Wong Cynthia, Vuong Jett, Nizkorodov Sergey A
Department of Chemistry, University of California, Irvine, Irvine, California 92697-2025, United States.
J Phys Chem A. 2024 Sep 12;128(36):7657-7668. doi: 10.1021/acs.jpca.4c04287. Epub 2024 Aug 30.
Primary biological aerosol particles (PBAPs) and secondary organic aerosol (SOA) both contain organic compounds that share similar chemical and optical properties. Fluorescence is often used to characterize PBAPs; however, this may be hindered due to interferences from fluorophores in SOA. Despite extensive efforts to understand the aging of SOA under elevated particle acidity conditions, little is known about how these processes affect the fluorescence of SOA and thereby their interference with the measurements of PBAPs. The objective of this study is to investigate the fluorescence of SOA and understand the influence of acidity on the optical properties of organic aerosols and potential interference for the analysis of bioaerosols. The SOA was generated by O- or OH-initiated oxidation of d-limonene or α-pinene, as well as by OH-initiated oxidation of toluene or xylene. The SOA compounds were then aged by exposure to varying concentrations of aqueous HSO for 2 days. Absorption and fluorescence spectrophotometry were used to examine the changes in the optical properties before and after aging. The key observation was the appearance of strongly light-absorbing and fluorescent compounds at pH = ∼-1, suggesting that acidity is a major driver of SOA aging. The aged SOA from biogenic precursors (d-limonene and α-pinene) resulted in stronger fluorescence than the aged SOA from toluene and xylene. The absorption spectra of the aged SOA changed drastically in shape upon dilution, whereas the shapes of the fluorescence spectra remained the same, suggesting that the fluorophores and chromophores in SOA are separate sets of species. The fluorescence spectra of aged SOA overlapped with the fluorescence spectra of PBAPs, suggesting that SOA exposed to highly acidic conditions can be confused with PBAPs detected by fluorescence-based methods. These processes are likely to play a role in the atmospheric regions where high concentrations of HSO persist, such as the upper troposphere and lower stratosphere.
原生生物气溶胶颗粒（PBAPs）和二次有机气溶胶（SOA）都含有具有相似化学和光学性质的有机化合物。荧光常用于表征PBAPs；然而，由于SOA中荧光团的干扰，这一过程可能会受到阻碍。尽管人们为了解颗粒酸度升高条件下SOA的老化付出了巨大努力，但对于这些过程如何影响SOA的荧光，进而影响其对PBAPs测量的干扰却知之甚少。本研究的目的是研究SOA的荧光，了解酸度对有机气溶胶光学性质的影响以及对生物气溶胶分析的潜在干扰。SOA通过d - 柠檬烯或α-蒎烯的O - 或OH引发氧化，以及甲苯或二甲苯的OH引发氧化生成。然后将SOA化合物暴露于不同浓度的HSO水溶液中2天进行老化。采用吸收和荧光分光光度法检测老化前后光学性质的变化。关键观察结果是在pH值约为 - 1时出现了强吸光和荧光化合物，这表明酸度是SOA老化的主要驱动因素。来自生物源前体（d - 柠檬烯和α-蒎烯）的老化SOA产生的荧光比来自甲苯和二甲苯的老化SOA更强。老化SOA的吸收光谱在稀释时形状发生了剧烈变化，而荧光光谱的形状保持不变，这表明SOA中的荧光团和发色团是不同的物种集合。老化SOA的荧光光谱与PBAPs的荧光光谱重叠，这表明暴露于高酸性条件下的SOA可能会与基于荧光的方法检测到的PBAPs混淆。这些过程可能在高浓度HSO持续存在的大气区域中起作用，如对流层上部和平流层下部。
