Observations of highly oxidized molecules and particle nucleation in the atmosphere of Beijing
Observations of highly oxidized molecules and particle nucleation in the atmosphere of Beijing
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DOI：
10.5194/acp-19-14933-2019
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发表时间：
2019-12-10
影响因子：
6.3
通讯作者：
Lee, James
中科院分区：
文献类型：
--
作者：
Brean, James;Harrison, Roy M.;Lee, James
粒子成核是大气颗粒物数量的主要来源之一，新粒子对人类健康和气候具有重大影响。高度氧化的多功能有机分子（HOMs）最近被确定为新粒子生长以及有时初始形成的关键成分。虽然在大气舱、流管和清洁环境中对HOMs进行了许多研究，但对污染环境数据的分析却很少。在此，展示了对HOMs以及小到分子簇的粒径分布的测量结果，同时还有2017年6月在北京一次活动中测得的挥发性有机化合物（VOCs）和痕量气体数据。对许多气相HOMs进行了表征，并在新粒子形成的背景下分析了它们的时间趋势和行为。所确定的HOMs的氧化程度与在其他更清洁的环境中所见的相当，这可能是由于较高温度促进快速夺氢以及较高浓度的NOx和其他RO₂·终止剂更快地终止自氧化序列之间的相互作用。我们的数据表明，烷基苯、单萜和异戊二烯是北京HOMs的重要前体挥发性有机化合物。许多来自异戊二烯和单萜的C - 5和C - 10化合物的平均碳氧化态比来自其他前体的略高。除了大二聚体之外，大多数HOMs在白天达到浓度峰值，这表明OH·化学在HOMs形成中的重要性，因为在HOM浓度较高的日子里O₃往往较低；同样，在HOM浓度较高的日子里VOC浓度也较低。HOMs的白天峰值与新形成的粒子的生长相吻合，它们的初始形成与硫酸蒸汽的峰值相吻合，这表明成核过程依赖于硫酸，HOMs对后续的粒子生长有贡献。
Particle nucleation is one of the main sources of atmospheric particulate matter by number, with new particles having great relevance for human health and climate. Highly oxidized multifunctional organic molecules (HOMs) have been recently identified as key constituents in the growth and, sometimes, in initial formation of new particles. While there have been many studies of HOMs in atmospheric chambers, flow tubes, and clean environments, analyses of data from polluted environments are scarce. Here, measurements of HOMs and particle size distributions down to small molecular clusters are presented alongside volatile organic compounds (VOCs) and trace-gas data from a campaign in June 2017, in Beijing. Many gas-phase HOMs have been characterized and their temporal trends and behaviours analysed in the context of new particle formation. The HOMs identified have a degree of oxidation comparable to that seen in other, cleaner, environments, likely due to an interplay between the higher temperatures facilitating rapid hydrogen abstractions and the higher concentrations of NOx and other RO2 center dot terminators ending the autoxidation sequence more rapidly. Our data indicate that alkylbenzenes, monoterpenes, and isoprene are important precursor VOCs for HOMs in Beijing. Many of the C-5 and C-10 compounds derived from isoprene and monoterpenes have a slightly greater degree of average oxidation state of carbon compared to those from other precursors. Most HOMs except for large dimers have daytime peak concentrations, indicating the importance of OH center dot chemistry in the formation of HOMs, as O-3 tends to be lower on days with higher HOM concentrations; similarly, VOC concentrations are lower on the days with higher HOM concentrations. The daytime peaks of HOMs coincide with the growth of freshly formed new particles, and their initial formation coincides with the peak in sulfuric acid vapours, suggesting that the nucleation process is sulfuric-acid-dependent, with HOMs contributing to subsequent particle growth.