在存在硫酸的情况下蒸发次要有机物质提取物期间形成吸光性有机硫酸盐,ACS Earth and Space Chemistry

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在存在硫酸的情况下蒸发次要有机物质提取物期间形成吸光性有机硫酸盐
ACS Earth and Space Chemistry ( IF 2.9 ) Pub Date : 2019-05-16 00:00:00 , DOI: 10.1021/acsearthspacechem.9b00036
Lauren T. Fleming ₁ , Nujhat N. Ali ₁ , Sandra L. Blair ₁ , Marie Roveretto ₂ , Christian George ₂ , Sergey A. Nizkorodov ₁

Affiliation

有机气溶胶通过散射或吸收入射的太阳辐射来影响气候。代表大气气溶胶颗粒主要化学成分的二次有机材料（SOM）是通过大气挥发性有机化合物（VOC）的氧化而产生的。云，雾和气溶胶中的SOM由于水滴的蒸发/冷凝而经历浓缩/稀释循环。这些物理过程可能导致SOM的化学处理，并形成新的吸光化合物。在这项研究中，模型SOM是通过烟雾舱光氧化和流管臭氧分解各种与大气有关的人为和生物来源的VOC（包括甲苯（TOL），d-柠檬烯（LIM），α-pine烯（APIN），β-pine烯（BPIN）和异戊二烯（ISO）。收集的SOM用水萃取，溶液用硫酸酸化至pH 2并干燥以模拟包含SOM的酸性颗粒的蒸发。在硫酸存在下蒸发和再溶解SOM后，观察到质量吸收系数（MACs）发生了显着变化。在可见波长处，大多数SOM的MAC值在蒸发后增加，而分数增加是LIM / O ₃ SOM在400 nm处最大的部分（分数增加65.0）。在硫酸存在下蒸发增加MAC值的例外是ISO / OH和TOL / OH / NO _x。LIM / O _3中的吸光物质SOM进行色谱分离，并使用光电二极管阵列检测器和高分辨率电喷雾电离质谱仪进行检测。MAC的增加伴随着300多个有机硫酸盐峰的出现。分离了LIM / O ₃ SOM中五个潜在的棕碳（BrC）发色团并指定了化学式，包括C ₁₀ H ₁₆ SO ₆，C ₁₀ H ₁₄ SO ₆，C ₁₀ H ₁₆ SO ₅，C ₁₁ H ₁₆ SO ₇，和C ₁₁ H ₁₈ SO ₈。这项研究表明，蒸发驱动的过程可能发生在大气中，从而大大改变了SOM的分子组成和光学性质。如果提取物在蒸发之前具有足够的酸性，则其从田间或实验室滤出物的蒸发会类似地产生有机硫酸盐作为伪影。我们建议在以后的工作中应避免完全干燥颗粒物过滤器提取物。

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Formation of Light-Absorbing Organosulfates during Evaporation of Secondary Organic Material Extracts in the Presence of Sulfuric Acid

Organic aerosols affect the climate by scattering or absorbing incoming solar radiation. Secondary organic material (SOM), which represents the major chemical constituent of atmospheric aerosol particles, is produced by the oxidation of atmospheric volatile organic compounds (VOCs). SOM in clouds, fogs, and aerosols undergoes concentration/dilution cycles due to the evaporation/condensation of water droplets. These physical processes could lead to the chemical processing of SOM and the formation of new, light-absorbing compounds. In this study, model SOM was generated through smog chamber photooxidation and flow tube ozonolysis of various atmospherically relevant anthropogenic and biogenic VOCs, including toluene (TOL), d-limonene (LIM), α-pinene (APIN), β-pinene (BPIN), and isoprene (ISO). Collected SOM was extracted in water, and the solutions were acidified with sulfuric acid to pH 2 and dried to simulate the evaporation of acidic particles containing SOM. Significant changes in mass absorption coefficients (MACs) were observed after the evaporation and redissolution of SOM in the presence of sulfuric acid. At visible wavelengths, the MAC values of most SOM increased after the evaporation, with the fractional increase being the largest for LIM/O₃ SOM at 400 nm (fractional increase of 65.0). Exceptions to evaporation increasing MAC values in the presence of sulfuric acid were ISO/OH and TOL/OH/NO_x. Light-absorbing species in LIM/O₃ SOM were chromatographically separated and detected using a photodiode array detector and a high-resolution electrospray ionization mass spectrometer. The increase in MAC was accompanied by the appearance of more than 300 organosulfate peaks. Five potential brown carbon (BrC) chromophores in LIM/O₃ SOM were separated and assigned chemical formulas, including C₁₀H₁₆SO₆, C₁₀H₁₄SO₆, C₁₀H₁₆SO₅, C₁₁H₁₆SO₇, and C₁₁H₁₈SO₈. This study suggests that evaporation-driven processes may occur in the atmosphere, substantially modifying the molecular composition and optical properties of SOM. The evaporation of filter extracts from the field or laboratory could similarly produce organosulfates as artifacts if the extract is sufficiently acidic before the evaporation. We recommend that complete drying of particulate matter filter extracts should be avoided in future work.

更新日期：2019-05-16

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