NO2 can be transformed into nitrite by the absorption of Rhodamine B solution, which will make fluorescence quenching of Rhodamine B in acidic medium. According to this mechanism, a new method for detecting nitrogen oxides in the air is developed by a fluorescence spectrophotometry. The influence of environmental media and interfering substances in the fluorescence intensity of system was studied. Under the optimal experimental conditions, the decrease of fluorescence intensity varies linearly with the concentration of NO2？？？ over the range of 0.009~0.500？μg/ml with a correlation coefficient of 0.9992. The method is simple and has a lower limit of detection than the common methods. It can be a referee for the environmental evaluation. 1. Introduction Nitrogen oxides are one of the main pollutants as well as the evaluation criteria of the air quality. Nitrogen oxides in the atmosphere have harmful effects on humans mainly through the respiratory system, which may cause acute and chronic poison. Therefore, the study of analysis and detection methods for nitrogen oxides will be significant. There are many methods for the determination of nitrogen oxides such as ion chromatography [1], chemiluminescence [2, 3], fluorescence [4], and colorimetric microdetermination [5]. However, the method that nitrogen oxides in the air were determined with Rhodamine B by fluorescence quenching has not been reported. Nitrogen oxides can exist in various forms including the main forms of NO and NO2 in the atmosphere. In this research, the contents of NO and NO2 in the air sample were determined indirectly by measuring the content of nitrite and solution absorption-fluorescence spectrometry. There are many methods for the determination of nitrite such as spectrophotometry [6–8], fluorescence [9–14], chemiluminescence [15–17], polarography [18] and chromatography [19–22]. Among these methods, the fluorescence method has attracted much attention and been applied widely for the detection of nitrite for the high sensitivity, selectivity, low limit of detection and simple operation. According to the literature, NO2？-organic dyes and NO2？-KBrO3？-organic dyes are the main systems for the determination of nitrite by the fluorescence spectrometry. The common determination of nitrogen oxides is Saltzman method [23, 24]. However, the contents of NO and NO2 in the actual air sample are determined with Rhodamine B by fluorescence quenching with quite satisfactory results. The method in the text is simple and has a lower limit of detection, which provides a referee for the assessment of
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