In order to investigate the kinetics and selectivity of the liquid phase nitration of phenol, reliable procedures for the production of the nitrating agents N₂O₅ and CINO₂ were established. Production of N₂O₅ was achieved via on-line mixing of NO₂ (1%) with O₃(~5%) in the 2:1 ratio in a darkened reaction vessel. CINO₂ was produced by conversion of N₂O₅ using NaCI solution (4 M). The concentration of nitrating agents was determined by bubbling the gas stream through water to yield nitrate which was analysed using Ion Chromatography and also by off-line reduction to nitrite followed by analysis using the sulphanilamide/UV method. A method for quantitative solid phase extraction with phenol in the aqueous phase. Nitration experiments were conducted under both acidic and basic conditions over a temperature range relevant to environmental processes. Results indicate the formation of 4-nitrosophenol (additionally characterised using GC-MS) as well as 2- and 4-nitrophenol (additionally characterised using GC-MS) as well as 2- and 4-nitrophenol. The product ratio of the products species has been shown to be dependent upon both the nitrating agent on pH. Finally, a chemical kinetic model has been developed to quantify the relative nitration pathways of aromatics in the troposphere. A box model, coded using FACSIMILE software, has been used to partitioning of benzene and phenol into the liquid phase and to assess the relative importance of the gas and liquid phases. The model includes the phase partitioning of 21 species and focuses on the conversion of benzene to phenol and finally nitrophenol in both the gas and liquid phase. Results indicate that the liquid phase contributes significantly to the production of nitrophenols in the troposphere. The system was shown to be sensitive to the assumed liquid water content over the range 3x10^-9 to 3x10^-6 as well as the droplet diameter and temperature. The accuracy of the liquid phase rate coefficients for the phenol + OH and phenol + NO₃ reactions were also shown to be very significant although altering the liquid phase benzene rate coefficient had little impact on the system as a whole. The model was also extending to include the partitioning of the nitrophenol products. This allowed an estimation to be made regarding the fate of the product species. At the benchmark Lc value of 3x10^-7, used to describe tropospheric cloud conditions, some 58% of the nitrophenols are produced by liquid phase processes whereas less than 2% of the nitrophenols remains in the liquid. This suggests that a great deal of the nitrophenol that may be observed in the gas phase is actually produced through liquid phase pathways.