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Optical Property Measurements and Single Particle Analysis of Secondary Organic Aerosol Produced from the Aqueous-Phase Reaction of Ammonium Sulfate with Methylglyoxal
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2018-02-27 00:00:00 , DOI: 10.1021/acsearthspacechem.8b00004 Deokhyeon Kwon 1 , Victor W. Or 2 , Matthew J. Sovers 1 , Mingjin Tang 1 , Paul D. Kleiber 3 , Vicki H. Grassian 2, 4 , Mark A. Young 1
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2018-02-27 00:00:00 , DOI: 10.1021/acsearthspacechem.8b00004 Deokhyeon Kwon 1 , Victor W. Or 2 , Matthew J. Sovers 1 , Mingjin Tang 1 , Paul D. Kleiber 3 , Vicki H. Grassian 2, 4 , Mark A. Young 1
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Reactions involving the dicarbonyl species methylglyoxal (MG) have been suggested as an important pathway for the production of secondary organic aerosol (SOA) in the atmosphere. Reaction in an aqueous inorganic salt solution, such as ammonium sulfate (AS), leads to the formation of light-absorbing brown carbon (BrC) product. We report on an investigation of the optical properties of BrC aerosol generated from the aqueous-phase reaction between MG and AS as a function of aging time using calibrated cavity ring-down spectroscopy (CRDS) at a wavelength of 403 nm. The retrieved real index of refraction at 403 nm is n = 1.558 ± 0.021, with an imaginary index value of k = 0.002 ± 0.004; these values do not appear to change significantly with aging time over the course of 22 days and are similar to the AS aerosol values. The small complex index suggests that BrC aerosol formed from this pathway may not significantly impact radiative forcing. Measurements of the aerosol optical properties show significant deviation from Mie theory simulations for particles with diameters of ≳500 nm, probably as a result of nonspherical particle shape effects. In addition to the CRDS study, we used UV–vis spectroscopy to measure the mass absorption coefficient of the solution-phase reaction products as a function of aging. We also employed atomic force microscopy (AFM)-based IR spectroscopy to investigate the morphology and chemical composition of single SOA particles. AFM analysis of the particle morphology shows that a significant fraction of BrC particles with diameters of ≳500 nm are nonspherical in shape, consistent with our observed breakdown in the applicability of Mie theory for larger particles.
中文翻译：
硫酸铵与甲基乙二醛水相反应产生的次级有机气溶胶的光学性质测量和单颗粒分析
已经提出涉及二羰基甲基乙二醛（MG）的反应是在大气中产生次级有机气溶胶（SOA）的重要途径。在无机盐水溶液（例如硫酸铵（AS））中进行反应会导致形成吸光的棕碳（BrC）产物。我们报告了使用校准腔衰荡光谱法（CRDS）在403 nm波长下对MG和AS之间的水相反应产生的BrC气溶胶的光学特性进行研究的结果，该光学特性是老化时间的函数。检索到的在403 nm处的实际折射率为n = 1.558±0.021，虚拟折射率值为k= 0.002±0.004; 在22天的过程中，这些值似乎不会随着老化时间而发生显着变化，并且与AS气溶胶值相似。较小的综合指数表明，从该途径形成的BrC气溶胶可能不会显着影响辐射强迫。气溶胶光学性质的测量结果表明，对于直径≳500nm的颗粒，其Mie理论模拟存在明显偏差，这可能是由于非球形颗粒形状的影响所致。除CRDS研究外，我们还使用紫外可见光谱法测量了溶液相反应产物的质量吸收系数与老化的关系。我们还使用了基于原子力显微镜（AFM）的红外光谱来研究单个SOA颗粒的形态和化学成分。
更新日期：2018-02-27
中文翻译：
硫酸铵与甲基乙二醛水相反应产生的次级有机气溶胶的光学性质测量和单颗粒分析
已经提出涉及二羰基甲基乙二醛（MG）的反应是在大气中产生次级有机气溶胶（SOA）的重要途径。在无机盐水溶液（例如硫酸铵（AS））中进行反应会导致形成吸光的棕碳（BrC）产物。我们报告了使用校准腔衰荡光谱法（CRDS）在403 nm波长下对MG和AS之间的水相反应产生的BrC气溶胶的光学特性进行研究的结果，该光学特性是老化时间的函数。检索到的在403 nm处的实际折射率为n = 1.558±0.021，虚拟折射率值为k= 0.002±0.004; 在22天的过程中，这些值似乎不会随着老化时间而发生显着变化，并且与AS气溶胶值相似。较小的综合指数表明，从该途径形成的BrC气溶胶可能不会显着影响辐射强迫。气溶胶光学性质的测量结果表明，对于直径≳500nm的颗粒，其Mie理论模拟存在明显偏差，这可能是由于非球形颗粒形状的影响所致。除CRDS研究外，我们还使用紫外可见光谱法测量了溶液相反应产物的质量吸收系数与老化的关系。我们还使用了基于原子力显微镜（AFM）的红外光谱来研究单个SOA颗粒的形态和化学成分。
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