Sun Mingrui, Smith Geoffrey D
Department of Chemistry, University of Georgia, Athens, Georgia 30602, United States.
ACS Earth Space Chem. 2024 Jul 11;8(8):1623-1633. doi: 10.1021/acsearthspacechem.4c00134. eCollection 2024 Aug 15.
Laboratory studies have shown that photolytic mass loss can be a significant sink for secondary organic aerosol (SOA). Here, we use a quartz crystal microbalance to measure mass loss of Suwannee River Humic Acid (SRHA) and Suwannee River Fulvic Acid (SRFA), surrogates for SOA, exposed to 254, 300, and 405 nm radiation over the course of 24 h. We find that the photolytic mass loss rates of these materials are comparable to those for laboratory-generated limonene and toluene SOA material from the study of Baboomian et al, . 1078. Scaling our results to ambient conditions, we estimate that humic substances in aerosols can lose as much as 8% by mass in the first day of exposure in the atmosphere, equivalent to 0.025% of , the photolysis rate of nitrogen dioxide. By using zero air instead of nitrogen, we also find that the presence of oxygen accelerates the photolytic mass loss rate by a factor of 2 to 4 at all wavelengths suggesting a potential role for reactive oxygen species. UV photolysis of an aqueous SRFA solution demonstrated both photobleaching at UV wavelengths and photoenhancement at visible wavelengths. Ultrahigh-resolution mass spectrometric analysis showed that condensed-phase SRFA photolysis led to decreased intensity in the 100-300 / range while aqueous SRFA photolysis resulted in an increase in intensity in the same range. This work reaffirms that photolytic mass loss is a potentially significant sink for SOA, but only on the time scale of a day or two and demonstrates that SRHA and SRFA are suitable surrogates for atmospheric SOA with respect to photolytic mass loss.
实验室研究表明，光解质量损失可能是二次有机气溶胶（SOA）的一个重要汇。在此，我们使用石英晶体微天平来测量暴露于254、300和405nm辐射下24小时的苏万尼河腐殖酸（SRHA）和苏万尼河富里酸（SRFA）（SOA的替代物）的质量损失。我们发现这些材料的光解质量损失率与Baboomian等人研究中实验室生成的柠檬烯和甲苯SOA材料的损失率相当。将我们的结果按比例推算至环境条件下，我们估计气溶胶中的腐殖物质在大气中暴露的第一天质量损失可达8%，相当于二氧化氮光解速率的0.025%。通过使用零空气而非氮气，我们还发现在所有波长下，氧气的存在使光解质量损失率加快了2至4倍，这表明活性氧物质可能发挥了作用。SRFA水溶液的紫外光解在紫外波长下表现出光漂白，在可见光波长下表现出光增强。超高分辨率质谱分析表明，凝聚相SRFA光解导致100 - 300 /范围内强度降低，而SRFA水溶液光解导致同一范围内强度增加。这项工作再次证实光解质量损失可能是SOA的一个重要汇，但仅在一两天的时间尺度上，并且表明就光解质量损失而言，SRHA和SRFA是大气SOA的合适替代物。
