State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China; University of Chinese Academy of Sciences, Beijing 100049, China.
State Key Laboratory of Loess and Quaternary Geology, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China; School of Human Settlements and Civil Engineering, Xi'an Jiaotong University, Xi'an 710049, China.
Sci Total Environ. 2014 Sep 15;493:1088-97. doi: 10.1016/j.scitotenv.2014.04.086. Epub 2014 Jun 10.
PM10 aerosols from the summit of Mt. Hua (2060 m a.s.l) in central China during the winter and summer of 2009 were analyzed for dicarboxylic acids, ketocarboxylic acids and α-dicarbonyls. Molecular composition of dicarboxylic acids (C2-C11) in the free tropospheric aerosols reveals that oxalic acid (C2, 399 ± 261 ng m(-3) in winter and 522 ± 261 ng m(-3) in summer) is the most abundant species in both seasons, followed by malonic (C3) and succinic (C4) acids, being consistent with that on ground levels. Most of the diacids are more abundant in summer than in winter, but adipic (C6) and phthalic (Ph) acids are twice lower in summer, suggesting more significant impact of anthropogenic pollution on the wintertime alpine atmosphere. Moreover, glyoxal (Gly) and methylglyoxal (mGly) are also lower in summer (12 ± 6.1 ng m(-3)) than in winter (22 ± 13 ng m(-3)). As both dicarbonyls are a major precursor of C2, their seasonal variation patterns, which are opposite to those of the diacids, indicate that the mountain troposphere is more oxidative in summer. C2 showed strong linear correlations with levoglucosan in winter and oxidation products of isoprene and monoterpene in summer. PCA analysis further suggested that the wintertime C2 and related SOA in the Mt. Hua troposphere mostly originate from photochemical oxidations of anthropogenic pollutants emitted from biofuel and coal combustion in lowland regions. On contrast, the summertime C2 and related SOA mostly originate from further oxidation of the mountainous isoprene and monoterpene oxidation products. The AIM model calculation results showed that oxalic acid concentration well correlated with particle acidity (R(2)=0.60) but not correlated with particle liquid water content, indicating that particle acidity favors the organic acid formation because aqueous-phase C2 production is the primary mechanism of C2 formation in ambient aerosols and is driven by acid-catalyzed oxidation.
2009 年冬季和夏季，在中国中部华山（海拔 2060 米）山顶采集的 PM10 气溶胶，用于分析二羧酸、酮羧酸和α-二羰基化合物。在自由对流层气溶胶中二羧酸（C2-C11）的分子组成表明，冬季草酸（C2，399±261ngm-3）和夏季 522±261ngm-3）是最丰富的物种，其次是丙二酸（C3）和琥珀酸（C4），与地面水平一致。大多数二羧酸在夏季比冬季更丰富，但己二酸（C6）和邻苯二甲酸（Ph）在夏季降低了两倍，这表明人为污染对冬季高山大气的影响更为显著。此外，乙醛（Gly）和甲基乙二醛（mGly）在夏季（12±6.1ngm-3）也低于冬季（22±13ngm-3）。由于这两种二羰基化合物都是 C2 的主要前体，它们的季节性变化模式与二羧酸相反，这表明夏季山地对流层的氧化性更强。C2 在冬季与左旋葡聚糖呈强烈线性相关，在夏季与异戊二烯和单萜的氧化产物呈线性相关。PCA 分析进一步表明，华山对流层冬季的 C2 和相关的 SOA 主要来自低地生物燃料和煤炭燃烧排放的人为污染物的光化学氧化。相比之下，夏季的 C2 和相关的 SOA 主要来自山区异戊二烯和单萜氧化产物的进一步氧化。AIM 模型计算结果表明，草酸浓度与颗粒酸度（R2=0.60）高度相关，但与颗粒液态水含量无关，这表明颗粒酸度有利于有机酸的形成，因为在环境气溶胶中，C2 的形成主要是通过酸催化氧化的水相 C2 生成机制。
