Division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA, USA.
J Phys Chem A. 2010 Jan 21;114(2):913-34. doi: 10.1021/jp908530s.
The current work focuses on the detailed evolution of the chemical composition of both the gas- and aerosol-phase constituents produced from the OH-initiated photooxidation of naphthalene under low- and high-NO(x) conditions. Under high-NO(x) conditions ring-opening products are the primary gas-phase products, suggesting that the mechanism involves dissociation of alkoxy radicals (RO) formed through an RO(2) + NO pathway, or a bicyclic peroxy mechanism. In contrast to the high-NO(x) chemistry, ring-retaining compounds appear to dominate the low-NO(x) gas-phase products owing to the RO(2) + HO(2) pathway. We are able to chemically characterize 53-68% of the secondary organic aerosol (SOA) mass. Atomic oxygen-to-carbon (O/C), hydrogen-to-carbon (H/C), and nitrogen-to-carbon (N/C) ratios measured in bulk samples by high-resolution electrospray ionization time-of-flight mass spectrometry (HR-ESI-TOFMS) are the same as the ratios observed with online high-resolution time-of-flight aerosol mass spectrometry (HR-ToF-AMS), suggesting that the chemical compositions and oxidation levels found in the chemically-characterized fraction of the particle phase are representative of the bulk aerosol. Oligomers, organosulfates (R-OSO(3)), and other high-molecular-weight (MW) products are not observed in either the low- or high-NO(x) SOA; however, in the presence of neutral ammonium sulfate seed aerosol, an organic sulfonic acid (R-SO(3)), characterized as hydroxybenzene sulfonic acid, is observed in naphthalene SOA produced under both high- and low-NO(x) conditions. Acidic compounds and organic peroxides are found to account for a large fraction of the chemically characterized high- and low-NO(x) SOA. We propose that the major gas- and aerosol-phase products observed are generated through the formation and further reaction of 2-formylcinnamaldehyde or a bicyclic peroxy intermediate. The chemical similarity between the laboratory SOA and ambient aerosol collected from Birmingham, Alabama (AL) and Pasadena, California (CA) confirm the importance of PAH oxidation in the formation of aerosol within the urban atmosphere.
目前的工作重点是研究在低 NOx 和高 NOx 条件下，OH 引发的萘光氧化过程中所产生的气相和颗粒相成分的化学组成的详细演变。在高 NOx 条件下，开环产物是主要的气相产物，这表明该机制涉及通过 RO2+NO 途径或双环过氧机制形成的烷氧基自由基（RO）的离解。与高 NOx 化学相比，由于 RO2+HO2 途径，保留环的化合物似乎主导低 NOx 气相产物。我们能够对 53-68%的二次有机气溶胶（SOA）质量进行化学特征描述。通过高分辨率电喷雾电离飞行时间质谱（HR-ESI-TOFMS）在体相样品中测量的原子氧与碳（O/C）、氢与碳（H/C）和氮与碳（N/C）比值与在线高分辨率飞行时间气溶胶质谱（HR-ToF-AMS）观察到的比值相同，这表明在颗粒相化学特征部分中发现的化学成分和氧化水平代表了整个气溶胶。在低 NOx 和高 NOx SOA 中均未观察到低聚物、有机硫酸盐（R-OSO3）和其他高分子量（MW）产物；然而，在中性硫酸铵种子气溶胶的存在下，在高 NOx 和低 NOx 条件下产生的萘 SOA 中观察到一种有机磺酸（R-SO3），被表征为羟基苯磺酸。在化学特征化的高和低 NOx SOA 中发现酸性化合物和有机过氧化物占很大比例。我们提出，观察到的主要气相和颗粒相产物是通过 2-糠醛或双环过氧中间体的形成和进一步反应生成的。实验室 SOA 与从阿拉巴马州伯明翰（AL）和加利福尼亚州帕萨迪纳（CA）收集的环境气溶胶之间的化学相似性证实了 PAH 氧化在城市大气气溶胶形成中的重要性。
