Air Pollution Research Center, University of California , Riverside, California 92521, United States.
Environ Sci Technol. 2013 Aug 6;47(15):8434-42. doi: 10.1021/es401789x. Epub 2013 Jul 18.
Reactions of ambient particles collected from four sites within the Los Angeles, CA air basin and Beijing, China with a mixture of N2O5, NO2, and NO3 radicals were studied in an environmental chamber at ambient pressure and temperature. Exposures in the chamber system resulted in the degradation of particle-bound PAHs and formation of molecular weight (mw) 247 nitropyrenes (NPYs) and nitrofluoranthenes (NFLs), mw 273 nitrotriphenylenes (NTPs), nitrobenz[a]anthracenes (NBaAs), nitrochrysene (NCHR), and mw 297 nitrobenzo[a]pyrene (NBaP). The distinct isomer distributions resulting from exposure of filter-adsorbed deuterated fluoranthene to N2O5/NO3/NO2 and that collected from the chamber gas-phase suggest that formation of NFLs in ambient particles did not occur by NO3 radical-initiated reaction but from reaction of N2O5, presumably subsequent to its surface adsorption. Accordingly, isomers known to result from gas-phase radical-initiated reactions of parent PAHs, such as 2-NFL and 2- and 4-NPY, were not enhanced from the exposure of ambient particulate matter to N2O5/NO3/NO2. The reactivity of ambient particles toward nitration by N2O5/NO3/NO2, defined by relative 1-NPY formation, varied significantly, with the relative amounts of freshly emitted particles versus aged particles (particles that had undergone atmospheric chemical processing) affecting the reactivity of particle-bound PAHs toward heterogeneous nitration. Analyses of unexposed ambient samples suggested that, in nighttime samples where NO3 radical-initiated chemistry had occurred, heterogeneous formation of 1-NPY on ambient particles may have contributed to the ambient 1-NPY concentrations at downwind receptor sites. These results, together with observations that 2-NFL is consistently the dominant particle-bound nitro-PAH measured in ambient atmospheres, suggest that for PAHs that exist in both the gas- and particle-phase, the heterogeneous formation of particle-bound nitro-PAHs is a minor formation route compared to gas-phase formation.
在环境压力和温度下的环境室中，研究了从加利福尼亚州洛杉矶盆地和中国北京的四个地点收集的环境颗粒与 N2O5、NO2 和 NO3 自由基的混合物的反应。在腔室系统中的暴露导致颗粒结合的 PAHs 降解，并形成分子量 (mw) 为 247 的硝基苊 (NPYs) 和硝基荧蒽 (NFLs)、mw 为 273 的硝基三苯 (NTPs)、硝基苯并[a]蒽 (NBaAs)、硝基苊 (NCHR) 和 mw 为 297 的硝基苯并[a]芘 (NBaP)。从吸附在滤纸上的氘化荧蒽暴露于 N2O5/NO3/NO2 和从腔室气相中收集的明显的异构体分布表明，环境颗粒中 NFLs 的形成不是由 NO3 自由基引发的反应引起的，而是由 N2O5 引起的，可能是在其表面吸附之后。相应地，已知从母体 PAHs 的气相自由基引发反应中形成的异构体，例如 2-NFL 和 2-和 4-NPY，并未因暴露于 N2O5/NO3/NO2 而增强。N2O5/NO3/NO2 对环境颗粒的硝化反应性，用相对 1-NPY 形成来定义，变化很大，新鲜排放颗粒与老化颗粒（经历大气化学处理的颗粒）的相对量影响颗粒结合 PAHs 对非均相硝化的反应性。对未暴露的环境样品的分析表明，在夜间发生了 NO3 自由基引发的化学过程的情况下，1-NPY 可能在环境颗粒上的非均相形成可能导致下风受体位点的环境 1-NPY 浓度增加。这些结果，以及观察到 2-NFL 始终是在环境大气中测量的颗粒结合硝基-PAH 中的主要颗粒结合物，表明对于同时存在于气相和颗粒相中的 PAHs，颗粒结合硝基-PAH 的非均相形成是一种较小的形成途径，与气相形成相比。
