Secondary organic aerosol formation from camphene oxidation: measurements and modeling
Secondary organic aerosol formation from camphene oxidation: measurements and modeling
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DOI：
10.5194/acp-22-3131-2022
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发表时间：
2022-03-09
影响因子：
6.3
通讯作者：
Cocker, David R., III
中科院分区：
文献类型：
--
作者：
Li, Qi;Jiang, Jia;Cocker, David R., III
虽然异戊烯是在生物源和热解排放样品中测得的主要单萜之一，但在环境室中对异戊烯的氧化尚未进行充分研究，并且对其形成二次有机气溶胶（SOA）的潜力知之甚少。室衍生SOA数据的缺乏可能会导致显着的不确定性，SOA的预测从单萜氧化使用现有的参数化时，单萜是一个显着的贡献者总单萜。因此，为了促进对异戊烯氧化和SOA形成的理解，并提高异戊烯在空气质量模型中的代表性，在加州大学滨江环境室中进行了一系列实验，以探索异戊烯SOA质量产率和在大气相关OH浓度下在一系列化学条件下的性质。实验结果进行了比较，使用两个化学详细的箱模型：全州空气污染研究中心（SAPRC）和发电机显式化学和动力学的有机物在大气中（GECKO-A）的建模模拟。SOA的参数化来自使用两个产品和挥发性基集（VBS）的方法从商会的数据。添加氮氧化物（NOx）进行的实验导致比不添加NOx进行的实验（高达28%）更高的SOA质量产率（高达64%）。此外，在较低的质量负载下，异戊烯SOA质量产率随着SOA质量（Mo）而增加，但在较高的质量负载下达到阈值，其中SOA质量产率不再随着Mo而增加。SAPRC模拟室的研究表明，在较高的初始氮氧化物水平较高的SOA质量产率主要是由于较高的生产过氧自由基（RO 2）和生成的高含氧有机分子（HOM）形成通过单分子RO 2反应。SAPRC预测，在NOx的存在下，异戊二烯R 02与NO反应，并且所得R 02经历氢（H）-变换异构化反应;如先前已经记载的，这样的反应快速地添加氧并且导致具有非常低的挥发性的产物（即，HOMs）。在NOx存在下形成的终产物具有比通过初始异丙基烯RO 2与过氧化氢自由基（HO 2）或其它RO 2反应形成的那些显著更低的挥发性和更高的O：C比。进一步的分析揭示了极端NOx状态的存在，其中SOA质量产率由于高NO /HO 2比而再次被抑制。此外，发现随着[HC]（0）= [NOx]（0）增加和O：C降低，颗粒密度从1.47 g cm（3）降低到1.30 g cm（3）。所观察到的SOA质量产率的差异在很大程度上解释了气相RO 2化学和RO 2 + HO 2，RO 2 + NO，RO 2 + RO 2和RO 2自氧化反应之间的竞争。
While camphene is one of the dominant monoterpenes measured in biogenic and pyrogenic emission samples, oxidation of camphene has not been well-studied in environmental chambers and very little is known about its potential to form secondary organic aerosol (SOA). The lack of chamber-derived SOA data for camphene may lead to significant uncertainties in predictions of SOA from oxidation of monoterpenes using existing parameterizations when camphene is a significant contributor to total monoterpenes. Therefore, to advance the understanding of camphene oxidation and SOA formation and to improve representation of camphene in air quality models, a series of experiments was performed in the University of California Riverside environmental chamber to explore camphene SOA mass yields and properties across a range of chemical conditions at atmospherically relevant OH concentrations. The experimental results were compared with modeling simulations obtained using two chemically detailed box models: Statewide Air Pollution Research Center (SAPRC) and Generator for Explicit Chemistry and Kinetics of Organics in the Atmosphere (GECKO-A). SOA parameterizations were derived from the chamber data using both the two-product and volatility basis set (VBS) approaches. Experiments performed with added nitrogen oxides (NOx) resulted in higher SOA mass yields (up to 64 %) than experiments performed without added NOx (up to 28 %). In addition, camphene SOA mass yields increased with SOA mass (Mo) at lower mass loadings, but a threshold was reached at higher mass loadings in which the SOA mass yields no longer increased with Mo. SAPRC modeling of the chamber studies suggested that the higher SOA mass yields at higher initial NOx levels were primarily due to higher production of peroxy radicals (RO2) and the generation of highly oxygenated organic molecules (HOMs) formed through unimolecular RO2 reactions. SAPRC predicted that in the presence of NOx, camphene RO2 reacts with NO and the resultant RO2 undergoes hydrogen (H)-shift isomerization reactions; as has been documented previously, such reactions rapidly add oxygen and lead to products with very low volatility (i.e., HOMs). The end products formed in the presence of NOx have significantly lower volatilities, and higher O: C ratios, than those formed by initial camphene RO2 reacting with hydroperoxyl radicals (HO2) or other RO2. Further analysis reveals the existence of an extreme NOx regime, wherein the SOA mass yield can be suppressed again due to high NO / HO2 ratios. Moreover, particle densities were found to decrease from 1.47 to 1.30 g cm(3) as [HC](0) = [NOx](0) increased and O: C decreased. The observed differences in SOA mass yields were largely explained by the gas-phase RO2 chemistry and the competition between RO2 + HO2, RO2 + NO, RO2 + RO2, and RO2 autoxidation reactions.