GB/T 13906-92 Air Quality -- Determination of Nitrogen Oxides
This Standard GB/T 13906-92 specifies a method for determining nitrogen oxides in normal atmospheres. It is applicable to the determination of the concentration and transformation rate of nitrogen oxides in the atmosphere.
The main principle of the method is: the NO
2 and NO generated in the atmosphere are absorbed in the water solution of potassium hydroxide or sodium hydroxide, and the total amount of nitrogen oxides is determined by redox photmetric method.
The test equipment includes a sampling apparatus, a NOx alkali absorption apparatus, and a redox photometric waterproof meter.
Sampling should be conducted in the open atmosphere without external interference, and the sampling time should generally be not less than 4 h.
The sample should be drawn from the maximum possible height, usually up to 5 m. The sampling flow rate should exceed 5L, and the sample volume should not be less than 2L.
The sample should be stored in an alkaline solution of potassium hydroxide or sodium hydroxide within 48h, and the NO and NO2 in the sample should be absorbed according to their electrolytic voltammetric characteristics in the alkali solution.
The redox photometric water meter is then used to detect the concentration of nitrogen oxides in the sample. This method involves measuring the oxidation-reduction potential of the sample and converting the oxidation-reduction potential into the corresponding concentration of nitrogen oxides in the air, referred to as the standard reaction concentration (SRC).
The actual concentration of nitrogen oxides in the atmosphere is calculated as the product of SRC and collection rate.
The fromaldehyde synthesis method is a direct sampling method for measuring nitrogen oxides in the atmosphere without chemical absorption and reduction.
The method relies on the catalytic conversion of oxides of nitrogen in the atmosphere to fromaldehyde, and the predetermined reaction formaldehyde concentration is converted into the corresponding nitrogen oxide concentration according to the experimental conditions.
The sampling process for measuring nitrogen oxides in the atmosphere should be operated under the standard atmospheric pressure and temperature conditions.
The sample is carried by a sampling pump and is drawn directly into the temperature and pressure-controlled sample room.
The sample collected in the sample room is then catalyzed by a heated CuO/ZnO catalyst to form formaldehyde, and the formaldehyde produced is limited by a metal layer to generate a cyclic anodal current. The anodal current is measured and converted into a concentration value of related nitrogen oxides by the formula.
In summary, GB/T 13906-92 stipulates the determination of nitrogen oxides under normal atmospheric conditions, and provides two different methods for measuring nitrogen oxides, namely alkaline absorption and formaldehyde synthesis. It is an important basis for determining the atmospheric nitrogen oxide concentration and controlling atmospheric pollution.
