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.

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Helichrysum italicum (Roth) G. Don (Asteraceae), also known as immortelle, usually grows in the Mediterranean area. The composition of the essential oil (EO) of immortelle is a mixture of various aromatic substances, mainly monoterpenes and sesquiterpenes. Distillation is the most widely used method for extraction of EO immortelle, although the yield is very low (<1%). In this work, we aim to investigate how the use of different distillation methods affects the yield and chemical composition of immortelle EO. For this purpose, we applied two conventional methods: steam distillation (SD) and hydrodistillation (HD), and a modern (environmentally friendly) technique—microwave-assisted distillation (MAD). Wild immortelles from four different locations in Croatia were collected and carefully prepared for extraction. Each sample was then analyzed by gas chromatography–mass spectrometry (GC-MS). GraphPad Prisma statistical software was used to study the statistics between different groups of connections and analyze the data on the number of connections. The results show that HD gives a significantly higher yield (0.31 ± 0.09%) compared to MAD (0.15 ± 0.03%) and SD (0.12 ± 0.04%). On the other hand, the highest number of chemical compounds was identified with MAD (95.75 ± 15.31%), and most of them are subordinate compounds with complex structures. SD isolated EOs are rich in derived acyclic compounds with the highest percentage of ketones. The results show that the application of different distillation methods significantly affects the composition of the obtained immortelle EO, considering the yield of EO, the number of isolated, derived and non-derived compounds, chemotypes and compounds with simple (acyclic) and complex structures.

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