A sensitive fluorimetric method for the determination of nitrogen oxides (NOx: NO+NO2) in air is described. Nitrogen dioxide (nitrogen monoxide was previously converted to nitrogen dioxide in oxide tubes) was aspirated through a fritted glass bubble at a flow rate of 500ml min-1 for 120min and fixed as nitrite, using 0.1 N NaOH as a trapping solution with the empirical absorption efficiency 0.74 and the stoichiometric factor 0.5. The method is based on the fluorescence quenching of a red-region fluorescent reagent, tetra-substituted amino aluminum phthalocyanine (TAAlPc), after being diazotized by nitrite. Under optimal conditions the linear range of the calibration curve for nitrite is 1-40ng ml-1 (NO2 0.24-9.6 ppb, v/v). The detection limit is 0.34ng ml-1 for nitrite (NO2 0.08 ppb, v/v) and the relative standard deviation for six replicate measurements of 15ng ml-1 nitrite is 3.2%. The method has been applied to the determination of nitrogen oxides in the air with satisfactory results. Typical gaseous co-pollutants such as SO2, H2S and HCHO did not interference the determination.