Absorption Cross Sections of 2-Nitrophenol in the 295–400 nm Region and Photolysis of 2-Nitrophenol at 308 and 351 nm

Abstract

2-Nitrophenol is an important component of "brown carbon" in the atmosphere. Photolysis is its dominant gas phase removal process. We have determined the gas phase absorption cross sections of 2-nitrophenol in the 295-400 nm region by using cavity ring-down spectroscopy. 2-Nitrophenol exhibits a broad absorption band over the wavelength region studied, with the peak absorption located at 345 nm. Absorption cross section values range between (2.86 ± 0.18) × 10 and (2.63 ± 0.31) × 10 cm/molecule over the 295-400 nm range. We have investigated the HONO, NO, and OH formation channels following the gas phase photolysis of 2-nitrophenol at 308 and 351 nm. Direct NO formation was not observed. HONO and OH are direct products from 2-nitrophenol photolysis. The average OH quantum yields from the photolysis of 0.5, 1.0, and 2.0 mTorr of 2-nitrophenol are 0.69 ± 0.07 and 0.70 ± 0.07 at 308 and 351 nm. The average HONO quantum yields are 0.34 ± 0.09 and 0.39 ± 0.07 at 308 and 351 nm. The OH and HONO quantum yields are independent of nitrogen carrier gas pressure in the 20-600 Torr range. Oxidant formation rate constants from 2-nitrophenol photolysis have been calculated. Discussions have been made concerning the role of 2-nitrophenol gas phase photolysis in the formation of atmospheric oxidants in regions of high anthropogenic emissions.

Laboratory Insights into the Diel Cycle of Optical and Chemical Transformations of Biomass Burning Brown Carbon Aerosols

“…This observation is consistent with previous studies on the chemical transformations of NACs and organonitrates, where faster direct photolysis than OH • reactions in their atmospheric losses was highlighted. 43 − 47 In short, photolysis lifetimes of minutes to hours have been estimated for many nitrophenols and organonitrates, while their lifetimes with respect to OH • reactions range from days to weeks during atmospheric transport. 43 − 45 , 48 − 50 Moreover, based on the lifetime, the second-order degradation kinetic rate for the reaction of OH • with ONs in NO 3 • -aged wood tar aerosols was estimated to be (2.4 ± 1.1) × 10 –13 cm 3 molecule –1 s –1 , which is comparable with the kinetics for most atmospheric relevant nitrophenols and organonitrates in the range of (2.6–67.2) × 10 –13 cm 3 molecule –1 s –1 .…”

Atmospheric Processing of Nitrophenols and Nitrocresols From Biomass Burning Emissions

“…Additionally, nitrophenols and nitrocresols are readily photolyzed due to their strong ultraviolet‐visible absorptivity (Chen et al, 2011; Jacobson, 1999). Owing to the presence of strong intramolecular hydrogen bonds between the –OH and –NO 2 moieties, photolysis of nitrophenols and nitrocresols over the 300–500 nm region is a proposed photolytic source of nitrous acid (HONO), an important precursor of OH radicals in the polluted environment (Bejan et al, 2006; Sangwan & Zhu, 2016). Another fate of nitrophenols and nitrocresols in the atmosphere is condensing onto aqueous/organic aerosols and cloud droplets leading to the formation of secondary organic aerosols (SOA).…”

Real-Time Probing of an Atmospheric Photochemical Reaction by Ultrashort Extreme Ultraviolet Pulses: Nitrous Acid Release from o-Nitrophenol

“…Nitrophenols (NPs) are produced by the combustion of wood or coal and are widely distributed in the gas phase and in organic aerosols in the atmosphere. [1][2][3][4][5][6] NPs absorb sunlight and are photoreactive. 5,6 Their photolysis is considered as a source of nitrous acid (HONO).…”