Ozonation of p-nitrophenol at different pH values of water and the influence of radicals at acidic conditions

•Ozonation of p-nitrophenol was carried out at constant pH values of 2, 7 and 10.•Radical scavenger t-butanol was used for different t-butanol concentrations.•pH determines the relative production rates of the first intermediates.•Radicals play an important role in ozonation at low pH.•There exists t-butanol concentration for the slowest 4-nitrocathecol production.