The linear working range obtained for the method developed following procedure (I) was adequate for analysis of NO2 present in the ambient air of regions affected by anthropogenic activity [39]. Nevertheless, it is possible to increase the working range of the method. In the case of high concentrations of NO2, a reduction in the sampling time is the most convenient solution, as shown by the results presented in Fig.3a. For low concentrations of NO2, long sampling times can be avoided by reducing the volume of the solution used to solubilize the analyte collected in the C-18 cartridge. In parallel, it would also be advantageous to reduce the volume of reagent employed to produce the dye, which would be in accordance with the principles of green chemistry.