Evaluation of the pathways of tropospheric nitrophenol formation from benzene and phenol using a multiphase model

Abstract

Abstract. Phenols are a major class of volatile organic compounds (VOC) whose reaction within, and partitioning between, the gas and liquid phases affects their lifetime within the atmosphere, the local oxidising capacity, and the extent of production of nitrophenols, which are toxic chemicals. In this work, a zero-dimension box model was constructed to quantify the relative importance of different nitration pathways, and partitioning into the liquid phase, of mono-aromatic compounds in order to help elucidate the formation pathways of 2-and 4-nitrophenol in the troposphere. The liquid phase contributed significantly to the production of nitrophenols for liquid water content (L c ) values exceeding 3×10 −9 , and for a range of assumed liquid droplet diameter, even though the resultant equilibrium partitioning to the liquid phase was much lower. For example, in a "typical" model scenario, with L c =3×10 −7 , 58% of nitrophenol production occurred in the liquid phase but only 2% of nitrophenol remained there, i.e. a significant proportion of nitrophenol observed in the gas phase may actually be produced via the liquid phase. The importance of the liquid phase was enhanced at lower temperatures, by a factor ∼1.5-2 at 278 K c.f. 298 K. The model showed that nitrophenol production was particularly sensitive to the values of the rate coefficients for the liquid phase reactions between phenol and OH or NO 3 reactions, but insensitive to the rate coefficient for the reaction between benzene and OH, thus identifying where further experimental data are required.

Observations of fine particulate nitrated phenols in four sites in northern China: concentrations, source apportionment, and secondary formation

“…It mainly included biomass burning in nearby farmlands and rural areas and smoke from restaurants and residential kitchens. The direct emission of nitrated phenols from biomass burning was confirmed and determined by several previous studies, with emission factors ranging from 0.4 to 11.1 mg kg −1 (Hoffmann et al, 2007;Iinuma et al, 2007;Wang et al, 2017b).…”

“…However, the formation pathways of nitrated phenols from the condensed phase remains more uncertain than those for the gas phase (Harrison et al, 2005a). Once formed in the gas phase, the phenols and nitrated phenols partition between the gas and particle phases according to their saturated vapor pressure (Nojima et al, 1975;Bolzacchini et al, 2001;Harrison et al, 2005b;Xu and Wang, 2013). Chow et al (2016) found evidence from field measurements that high levels of nitrated phenols in Hong Kong were associated with high concentrations of NO 2 .…”

“…Secondary nitrated phenols were produced from precursors along with the formation of O 3 and secondary inorganic aerosols. Secondary formation was shown to be an important source of nitrated phenols in atmosphere in recent field and modeling studies (Harrison et al, 2005b;Iinuma et al, 2010;Yuan et al, 2016).…”

Stable carbon isotope ratios of ambient secondary organic aerosols in Toronto

“…Aqueous phase formation of 4-nitrophenol has also been proposed by Harrison et al (2005), suggesting that once phenol is produced from the reaction of benzene and the OH radical, it partitions into the aqueous phase and reacts with NO 3 to form 4-nitrophenol, which then partitions favorably into the gas phase. Based on model calculations, the aqueous formation processes can have a substantial contribution to the total formation rate at high liquid water content, such as in clouds, but this process contributes less than 2 % to nitrophenol formation at low liquid water contents (Harrison et al, 2005).…”

Observations of nitrated phenols in four sites in North China: Concentrations, source apportionment, and secondary formation

“…Precursors such as phenols and cresols are emitted and produced via photochemical oxidation of benzenes, and nitration processes then occur with the participation of NO 2 . During this process, the phenols and nitrated phenols partition from time to time between the gas and particle phases according to their saturated vapor pressure (Nojima et al, 15 1975;Bolzacchini et al, 2001;Harrison et al, 2005b;Xu and Wang, 2013). Chow et al (2016) found evidence from field measurements that high levels of nitrated phenols in Hong Kong were associated with high concentrations of NO 2 .…”