Molecular understanding of the suppression of new-particle formation by isoprene
Molecular understanding of the suppression of new-particle formation by isoprene
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DOI：
10.5194/acp-20-11809-2020
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发表时间：
2020-10-20
影响因子：
6.3
通讯作者：
Curtius, Joachim
中科院分区：
文献类型：
--
作者：
Heinritzi, Martin;Dada, Lubna;Curtius, Joachim
大气蒸汽的成核产生了全球云凝结核的一半以上，因此对气候有重要影响。最近的研究表明，单萜烯（C10H16）氧化产生高氧产物，可以在有或没有硫酸的情况下成核。单萜烯主要由树木排放，通常与异戊二烯（C5H8）一起排放，后者在所有有机蒸汽中具有最高的全球排放量。先前的研究表明，异戊二烯抑制单萜烯形成新粒子，但这种抑制的原因仍存在争议。在这里，在CERN CLOUD室的大气条件下进行的实验中，我们表明异戊二烯降低了具有19或20个碳原子的高氧二聚体的产量，这推动了颗粒成核和早期生长，同时增加了具有14或15个碳原子的二聚体的产量。二聚体（分别称为C-20和C-15）是由单萜烯或异戊二烯产生的过氧化自由基对（RO2中心点）之间的终止反应产生的。与纯单萜烯条件相比，异戊二烯在1.7 nm处降低了成核速率（取决于异戊二烯与单萜烯的比例），在1.3和3.2 nm之间的颗粒生长速率大约减半。然而，在3.2 nm以上，C-15二聚体对二次有机气溶胶有贡献，并且生长速率不受异戊二烯的影响。我们进一步表明，羟基自由基（OH中心点）的增加减少了化学系统中粒子的形成，而不是像之前提出的那样增强了它，因为它增加了异戊二烯衍生的RO2中心点自由基，减少了C-20的形成。RO2中心点终止是决定高氧有机分子（HOM）分布及其成核能力的关键步骤。降低C-20产率的物种，如NO、HO2和异戊二烯，可以有效地减少生物成核和早期生长。因此，在所研究的特定大气区域中，有机气溶胶的形成速率将根据精确的环境条件而变化。
Nucleation of atmospheric vapours produces more than half of global cloud condensation nuclei and so has an important influence on climate. Recent studies show that monoterpene (C10H16) oxidation yields highly oxygenated products that can nucleate with or without sulfuric acid. Monoterpenes are emitted mainly by trees, frequently together with isoprene (C5H8), which has the highest global emission of all organic vapours. Previous studies have shown that isoprene suppresses new-particle formation from monoterpenes, but the cause of this suppression is under debate. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we show that isoprene reduces the yield of highly oxygenated dimers with 19 or 20 carbon atoms - which drive particle nucleation and early growth - while increasing the production of dimers with 14 or 15 carbon atoms. The dimers (termed C-20 and C-15, respectively) are produced by termination reactions between pairs of peroxy radicals (RO2 center dot) arising from monoterpenes or isoprene. Compared with pure monoterpene conditions, isoprene reduces nucleation rates at 1.7 nm (depending on the isoprene = monoterpene ratio) and approximately halves particle growth rates between 1.3 and 3.2 nm. However, above 3.2 nm, C-15 dimers contribute to secondary organic aerosol, and the growth rates are unaffected by isoprene. We further show that increased hydroxyl radical (OH center dot) reduces particle formation in our chemical system rather than enhances it as previously proposed, since it increases isoprene-derived RO2 center dot radicals that reduce C-20 formation. RO2 center dot termination emerges as the critical step that determines the highly oxygenated organic molecule (HOM) distribution and the corresponding nucleation capability. Species that reduce the C-20 yield, such as NO, HO2 and as we show isoprene, can thus effectively reduce biogenic nucleation and early growth. Therefore the formation rate of organic aerosol in a particular region of the atmosphere under study will vary according to the precise ambient conditions.