Mayorga Raphael, Chen Kunpeng, Raeofy Nilofar, Woods Megan, Lum Michael, Zhao Zixu, Zhang Wen, Bahreini Roya, Lin Ying-Hsuan, Zhang Haofei
Department of Chemistry, University of California, Riverside, California 92507, United States.
Department of Environmental Sciences, University of California, Riverside, California 92507, United States.
Environ Sci Technol. 2022 Jun 21;56(12):7761-7770. doi: 10.1021/acs.est.2c02345. Epub 2022 Jun 8.
Nitrogen-containing heterocyclic volatile organic compounds (VOCs) are important components of wildfire emissions that are readily reactive toward nitrate radicals (NO) during nighttime, but the oxidation mechanism and the potential formation of secondary organic aerosol (SOA) and brown carbon (BrC) are unclear. Here, NO oxidation of three nitrogen-containing heterocyclic VOCs, pyrrole, 1-methylyrrole (1-MP), and 2-methylpyrrole (2-MP), was investigated in chamber experiments to determine the effect of precursor structures on SOA and BrC formation. The SOA chemical compositions and the optical properties were analyzed using a suite of online and offline instrumentation. Dinitro- and trinitro-products were found to be the dominant SOA constituents from pyrrole and 2-MP, but not observed from 1-MP. Furthermore, the SOA from 2-MP and pyrrole showed strong light absorption, while that from 1-MP were mostly scattering. From these results, we propose that NO-initiated hydrogen abstraction from the 1-position in pyrrole and 2-MP followed by radical shift and NO addition leads to light-absorbing nitroaromatic products. In the absence of a 1-position hydrogen, NO addition likely dominates the 1-MP chemistry. We also estimate that the total SOA mass and light absorption from pyrrole and 2-MP are comparable to those from phenolic VOCs and toluene in biomass burning, underscoring the importance of considering nighttime oxidation of pyrrole and methylpyrroles in air quality and climate models.
含氮杂环挥发性有机化合物（VOCs）是野火排放的重要组成部分，在夜间易与硝酸根自由基（NO）发生反应，但其氧化机制以及二次有机气溶胶（SOA）和棕碳（BrC）的潜在形成尚不清楚。在此，通过室内实验研究了三种含氮杂环VOCs（吡咯、1-甲基吡咯（1-MP）和2-甲基吡咯（2-MP））的NO氧化过程，以确定前体结构对SOA和BrC形成的影响。使用一系列在线和离线仪器分析了SOA的化学成分和光学性质。发现二硝基和三硝基产物是吡咯和2-MP生成的SOA的主要成分，但在1-MP中未观察到。此外，2-MP和吡咯生成的SOA表现出强烈的光吸收，而1-MP生成的SOA大多为散射。基于这些结果，我们提出，NO引发的从吡咯和2-MP中1位的氢提取，随后自由基转移和NO加成，会生成吸光的硝基芳烃产物。在没有1位氢的情况下，NO加成可能主导1-MP的化学反应。我们还估计，吡咯和2-MP生成的SOA总质量和光吸收与生物质燃烧中酚类VOCs和甲苯生成的相当，这突出了在空气质量和气候模型中考虑吡咯和甲基吡咯夜间氧化的重要性。
