Evaluation of the pathways of tropospheric nitrophenol formation from benzene and phenol using a multiphase model M. A. J. Harrison1,*, M. R. Heal1, and J. N. Cape2 1School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh EH9 3JJ, UK 2Edinburgh Research Station, Centre for Ecology & Hydrology, Bush Estate, Penicuik, Midlothian, EH26 0QB, UK *current address: Hadley Centre, Met Office, FitzRoy Road, Exeter, EX1 3PB, UK
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
(Lc) values exceeding 3x10-9, 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 Lc=3x10-7, 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 278K c.f. 298K.
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 NO3 reactions, but insensitive to the rate
coefficient for the reaction between benzene and OH, thus identifying where
further experimental data are required.
Citation: Harrison, M. A. J., Heal, M. R., and Cape, J. N.: Evaluation of the pathways of tropospheric nitrophenol formation from benzene and phenol using a multiphase model, Atmos. Chem. Phys., 5, 1679-1695, doi:10.5194/acp-5-1679-2005, 2005.