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

[摘要] Phenols are a major class of volatile organic compounds (VOC) whose reactionwithin, and partitioning between, the gas and liquid phases affects theirlifetime within the atmosphere, the local oxidising capacity, and the extentof production of nitrophenols, which are toxic chemicals. In this work, azero-dimension box model was constructed to quantify the relative importanceof different nitration pathways, and partitioning into the liquid phase, ofmono-aromatic compounds in order to help elucidate the formation pathways of2- and 4-nitrophenol in the troposphere. The liquid phase contributedsignificantly to the production of nitrophenols for liquid water content(L_c) values exceeding 3x10^-9, and for a range of assumed liquiddroplet diameter, even though the resultant equilibrium partitioning to theliquid phase was much lower. For example, in a "typical" model scenario,with L_c=3x10^-7, 58% of nitrophenol production occurred inthe liquid phase but only 2% of nitrophenol remained there, i.e. asignificant proportion of nitrophenol observed in the gas phase may actuallybe produced via the liquid phase. The importance of the liquid phase wasenhanced at lower temperatures, by a factor ~1.5-2 at 278K c.f. 298K.The model showed that nitrophenol production was particularly sensitiveto the values of the rate coefficients for the liquid phase reactionsbetween phenol and OH or NO₃ reactions, but insensitive to the ratecoefficient for the reaction between benzene and OH, thus identifying wherefurther experimental data are required.

[学科分类] 大气科学