Effect of Solar Radiation on the Optical Properties and Molecular Composition of Laboratory Proxies of Atmospheric Brown Carbon
Effect of Solar Radiation on the Optical Properties and Molecular Composition of Laboratory Proxies of Atmospheric Brown Carbon
复制标题
DOI：
10.1021/es502515r
复制
发表时间：
2014-09-02
影响因子：
11.4
通讯作者：
Nizkorodov, Sergey A.
中科院分区：
文献类型：
--
作者：
Lee, Hyun Ji (Julie);Aiona, Paige Kuuipo;Nizkorodov, Sergey A.
大气中棕色碳气溶胶的来源、光学性质和化学组成都是不确定的，这使得估算其对辐射强迫的贡献具有挑战性。此外，BrC的光学性质可能会发生显着变化，在其大气老化。我们研究了光解的分子组成，质量吸收系数，和荧光的二次有机气溶胶（SOA）制备的高氮氧化物萘（NAP SOA）的影响。我们的实验旨在模拟溶解在云滴或雾滴中的NAP SOA化合物的光解过程。观察到NAP SOA的水溶液光漂白（即，失去吸收可见光辐射的能力），对于近紫外线（300 - 400 nm）吸收的损失，有效半衰期类似于15小时（太阳在其天顶）。NAP的SOA的分子组成被显着修改的光解，与平均SOA公式从C14.1H14.5O5.1N0.085到C11.8H14.9O4.5N0.023后，4小时的照射。然而，平均O/C比没有显着变化，这表明它不是一个很好的度量评估的程度，光解驱动的老化在NAP SOA（和一般的BrC）。与NAP SOA相比，由柠檬烯+臭氧SOA与氨蒸气（老化的LIM/O-3 SOA）反应产生的BrC材料的光漂白快得多，但它没有导致平均分子组成的显著变化。老化的LIM/O-3 SOA在450 - 600 nm范围内的特征吸光度衰减，有效半衰期为
Sources, optical properties, and chemical composition of atmospheric brown carbon (BrC) aerosol are uncertain, making it challenging to estimate its contribution to radiative forcing. Furthermore, optical properties of BrC may change significantly during its atmospheric aging. We examined the effect of photolysis on the molecular composition, mass absorption coefficient, and fluorescence of secondary organic aerosol (SOA) prepared by high-NOx photooxidation of naphthalene (NAP SOA). Our experiments were designed to model photolysis processes of NAP SOA compounds dissolved in cloud or fog droplets. Aqueous solutions of NAP SOA were observed to photobleach (i.e., lose their ability to absorb visible radiation) with an effective half-life of similar to 15 h (with sun in its zenith) for the loss of near-UV (300-400 nm) absorbance. The molecular composition of NAP SOA was significantly modified by photolysis, with the average SOA formula changing from C14.1H14.5O5.1N0.085 to C11.8H14.9O4.5N0.023 after 4 h of irradiation. However, the average O/C ratio did not change significantly, suggesting that it is not a good metric for assessing the extent of photolysis-driven aging in NAP SOA (and in BrC in general). In contrast to NAP SOA, the photobleaching of BrC material produced by the reaction of limonene + ozone SOA with ammonia vapor (aged LIM/O-3 SOA) was much faster, but it did not result in a significant change in average molecular composition. The characteristic absorbance of the aged LIM/O-3 SOA in the 450-600 nm range decayed with an effective half-life of