Li Yuanyuan, Hou Zhanfang, Wang Yachen, Huang Tonglin, Wang Yanhui, Ma Jiangkai, Chen Xiuna, Chen Aimei, Chen Min, Zhang Xiaoting, Meng Jingjing
School of Geography and Environment, Liaocheng University, Liaocheng 252000, China.
State Key Laboratory of Loess and Quaternary Geology, Key Laboratory of Aerosol Chemistry and Physics, Institute of Earth Environment, Chinese Academy of Sciences, Xi'an 710075, China.
Molecules. 2023 Aug 8;28(16):5939. doi: 10.3390/molecules28165939.
The molecular characteristics and formation mechanism of biogenic secondary organic aerosols (BSOAs) in the forested atmosphere are poorly known. Here, we report the temporal variations in and formation processes of BSOA tracers derived from isoprene, monoterpenes, and caryophyllene in PM samples collected at the foot of Mt. Huang (483 m a. s. l) in East China during the summer of 2019 with a 3 h time resolution. The concentrations of nearly all of the detected species, including organic carbon (OC), elemental carbon (EC), levoglucosan, and SIA (sum of SO, NO, and NH), were higher at night (19:00-7:00 of the next day) than in the daytime (7:00-19:00). In addition, air pollutants that accumulated by the dynamic transport of the mountain breeze at night were also a crucial reason for the higher BSOA tracers. Most of the BSOA tracers exhibited higher concentrations at night than in the daytime and peaked at 1:00 to 4:00 or 4:00 to 7:00. Those BSOA tracers presented strong correlations with O in the daytime rather than at night, indicating that BSOAs in the daytime were primarily derived from the photo-oxidation of BVOCs with O. The close correlations of BSOA tracers with SO and particle acidity (pH) suggest that BSOAs were primarily derived from the acid-catalyzed aqueous-phase oxidation. Considering the higher relative humidity and LWC concentration at night, the promoted aqueous oxidation was the essential reason for the higher concentrations of BSOA tracers at night. Moreover, levoglucosan exhibited a robust correlation with BSOA tracers, especially -caryophyllinic acid, suggesting that biomass burning from long-distance transport exerted a significant impact on BSOA formation. Based on a tracer-based method, the estimated concentrations of secondary organic carbon (SOC) derived from isoprene, monoterpenes, and caryophyllene at night (0.90 ± 0.57 µgC m) were higher than those (0.53 ± 0.34 µgC m) in the daytime, accounting for 14.5 ± 8.5% and 12.2 ± 5.0% of OC, respectively. Our results reveal that the BSOA formation at the foot of Mt. Huang was promoted by the mountain-valley breezes and anthropogenic pollutants from long-range transport.
森林大气中生物源二次有机气溶胶（BSOAs）的分子特征和形成机制尚不清楚。在此，我们报告了2019年夏季在中国东部黄山脚下（海拔483米）采集的PM样本中，源自异戊二烯、单萜和石竹烯的BSOA示踪剂的时间变化和形成过程，时间分辨率为3小时。几乎所有检测到的物种浓度，包括有机碳（OC）、元素碳（EC）、左旋葡聚糖和SIA（SO、NO和NH的总和），夜间（19:00至次日7:00）均高于白天（7:00至19:00）。此外，夜间山风动态输送积累的空气污染物也是BSOA示踪剂浓度较高的关键原因。大多数BSOA示踪剂夜间浓度高于白天，在1:00至4:00或4:00至7:00达到峰值。这些BSOA示踪剂在白天而非夜间与O表现出强相关性，表明白天的BSOAs主要源自BVOCs与O的光氧化。BSOA示踪剂与SO和颗粒酸度（pH）的密切相关性表明，BSOAs主要源自酸催化的水相氧化。考虑到夜间较高的相对湿度和LWC浓度，水相氧化的促进是夜间BSOA示踪剂浓度较高的根本原因。此外，左旋葡聚糖与BSOA示踪剂，尤其是石竹烯酸表现出强相关性，表明远距离传输的生物质燃烧对BSOA形成产生了重大影响。基于示踪剂方法，夜间源自异戊二烯、单萜和石竹烯的二次有机碳（SOC）估计浓度（0.90±0.57µgC m）高于白天（0.53±0.34µgC m），分别占OC的14.5±8.5%和12.2±5.0%。我们的结果表明，黄山脚下的BSOA形成受到山谷风以及远距离传输的人为污染物的促进。
