Atmospheric nitrophenols are pollutants of concern due to their toxicity and light-absorption characteristics and their low reactivity resulting in relatively long residence times in the environment. We investigate multiphase nitrophenol formation from guaiacol in a simulated atmospheric aerosol and support observations with the corresponding chemical mechanisms. The maximal secondary organic aerosol (SOA) yield (42%) is obtained under illumination at 80% relative humidity. Among the identified nitrophenols, 4-nitrocatechol (3.6% yield) is the prevailing species in the particulate phase. The results point to the role of water in catechol and further 4-nitrocatechol formation from guaiacol. In addition, a new pathway of dark nitrophenol formation is suggested, which prevailed in dry air and roughly yielded 1% nitroguaiacols. Furthermore, the proposed mechanism possibly leads to oligomer formation via a phenoxy radical formation by oxidation with HONO.

A substantial fraction of sub-micron tropospheric aerosol particles (20%-90%) consists of organic matter (Jimenez et al., 2009;Q. Zhang et al., 2007). Its formation can be attributed to either direct emission of primary organic aerosol or to reactions of organic compounds in the gas phase followed by condensation and chemical processing leading to secondary organic aerosol (SOA;Ervens et al., 2011). Currently, the total global SOA burden is modeled to range from 0.3 to 2.3 Tg (