Nitrophenols are a class of aromatic organic compounds that have gained much interest as a result of their widespread presence. Atmospheric sources include both primary sources, such as automobile engines and biomass burning, and secondary sources, by oxidation of phenols in presence of nitrogen oxides. Nitrophenols occur in both atmospheric gaseous and condensed phases. This work aims to elucidate the role of matrix effects in the photochemistry of a series of nitrophenols by investigating their photochemistry in solvents of different polarity and viscosity. Experiments conducted in 2-propanol solutions, as a proxy for a low-viscosity organic aerosol system, found drastically different atmospheric lifetimes between 2-nitrophenol (1000 hours), 4-nitrophenol (40 hours) and 2,4-dinitrophenol (4 hours). These nitrophenols were then incorporated into secondary organic aerosol (SOA) material on a quartz crystal microbalance (QCM) and irradiated at tropospherically relevant wavelengths (305 nm, 340 nm, and 405 nm). The mass loss of SOA was monitored by QCM, and the compositional changes in SOA and nitrophenol were monitored by ultra high-performance liquid chromatography coupled with a diode array detector and an Orbitrap mass spectrometer. For comparison, similar experiments were performed using traditional photosensitizers implanted in SOA instead of nitrophenols. Results from these studies will help constrain the sinks and reactivity of nitrophenols in atmospheric particulate matter.

Investigating the matrix effects in the photochemistry of atmospheric nitrophenols

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