Arellanes Chuautemoc, Paulson Suzanne E, Fine Philip M, Sioutas Constantinos
Department of Atmospheric and Oceanic Sciences, University of California, Los Angeles 90025, USA.
Environ Sci Technol. 2006 Aug 15;40(16):4859-66. doi: 10.1021/es0513786.
Simultaneous measurements of gas- and aerosol-phase hydrogen peroxide (H2O2) have been made at two sites in Los Angeles, one near the Pacific coast at the University of California at Los Angeles (UCLA), and the other in downtown Los Angeles with close proximity to a heavily traveled freeway (freeway site). At both the freeway and UCLA sites, gas-phase H2O2 levels were similar, averaging 1.17 +/- 1.0 and 1.05 +/- 0.6 ppb, respectively. The particle-associated H2O2 in both fine (PM2.5) and coarse (>PM2.5) modes was higher at the freeway site, as compared to UCLA, by a factor of 2. However, when aerosol-phase H2O2 is normalized to particle mass loadings, the fine-mode H2O2 levels are very similar at the two sites: 0.42 +/- 0.3 and 0.58 +/- 0.3 ng H2O2/microg particle mass at the freeway and UCLA sites, respectively. The normalized coarse-mode H2O2 levels were significantly higher at the freeway site than at UCLA, 1.05 +/- 0.3 and 0.51 +/- 0.3 ng/microg, respectively. Estimating aerosol liquid water content on the basis of relative humidity and aerosol mass, a calculated equivalent H2O2 in aerosol liquid water averages 70 mM, more than 2 orders of magnitude higher than concentrations predicted by gas-particle partitioning (Henry's law), which averages 0.1 mM. This indicates that the sampled particles are capable of generating H2O2 in aqueous solution. These corresponding aqueous-phase H2O2 concentrations in aerosol liquid water exceed levels that have been observed to produce cellular damage to lung epithelial cells in laboratory experiments by at least 3 orders of magnitude. Although most measurements of H2O2 in particles were made using an extraction solution adjusted to pH 3.5, a set of measurements indicates that H2O2 from fine-mode particles extracted in the physiologically relevant pH range 5-7.5 also generate H2O2 with only slightly lowered efficiency; coarse-mode H2O2 production dropped by 75% at the upper end of this range. Finally, a small set of measurements was performed to investigate the degree to which the recently developed Versatile Aerosol Concentrator Enrichment System (VACES) affects H2O2 levels in concentrated ambient aerosols. The VACES appeared to a have minimal impact on particulate H2O2.
在洛杉矶的两个地点同时进行了气相和气溶胶相过氧化氢（H₂O₂）的测量，一个地点位于加利福尼亚大学洛杉矶分校（UCLA）附近的太平洋海岸，另一个地点在洛杉矶市中心，靠近一条交通繁忙的高速公路（高速公路站点）。在高速公路站点和UCLA站点，气相H₂O₂水平相似，平均分别为1.17±1.0和1.05±0.6 ppb。与UCLA相比，高速公路站点细颗粒（PM₂.₅）和粗颗粒（>PM₂.₅）模式中与颗粒相关的H₂O₂含量高出2倍。然而，当将气溶胶相H₂O₂归一化到颗粒质量负荷时，两个站点的细颗粒模式H₂O₂水平非常相似：高速公路站点和UCLA站点分别为0.42±0.3和0.58±0.3 ng H₂O₂/μg颗粒质量。高速公路站点归一化后的粗颗粒模式H₂O₂水平显著高于UCLA站点，分别为1.05±0.3和0.51±0.3 ng/μg。根据相对湿度和气溶胶质量估算气溶胶液态水含量，计算得出的气溶胶液态水中等效H₂O₂平均为70 mM，比气-粒分配（亨利定律）预测的浓度（平均0.1 mM）高出2个数量级以上。这表明采样的颗粒能够在水溶液中生成H₂O₂。气溶胶液态水中这些相应的水相H₂O₂浓度超过了实验室实验中观察到的对肺上皮细胞产生细胞损伤的水平至少3个数量级。尽管大多数颗粒中H₂O₂的测量是使用pH值调至3.5的萃取溶液进行的，但一组测量表明，在生理相关pH范围5 - 7.5中萃取的细颗粒模式颗粒中的H₂O₂产生H₂O₂的效率仅略有降低；在该范围上限，粗颗粒模式H₂O₂产量下降了75%。最后，进行了一小部分测量，以研究最近开发的通用气溶胶浓缩富集系统（VACES）对浓缩环境气溶胶中H₂O₂水平的影响程度。VACES似乎对颗粒态H₂O₂的影响最小。
