Atmospheric NOx Measurement Experiment
Atmospheric NOx Measurement Experiment
Nitric oxides (Nitric oxides) in the air are NO, NO2, N2O, N2O3, N2O4, N2O5, etc., of which NO and NO2 are the main forms. Nitrogen oxides are generally generated through the combustion of nitrogen-containing organic matter, mainly from high-temperature combustion of fossil fuels, the production of nitric acid, nitrogen oxides fertilizer emissions and automobile exhaust emissions, etc., but also by the nitrogen fertilizer plants, chemical plants and ferrous metallurgical plants caused by the emission of three wastes.
Operation method
Naphthylenediamine hydrochloride spectrophotometric method
Principle
Glacial acetic acid, p-aminobenzene sulfonic acid and naphthalene ethylenediamine hydrochloride formulated into an absorbent solution, sampling of atmospheric nitrogen oxides through the oxidation tube in the form of NO2 is absorbed, generating nitrous acid and nitric acid, nitrous acid and p-aminobenzene sulfonic acid to play a diazotization reaction, and then coupled with naphthalene ethylenediamine hydrochloride to synthesize a rose-red nitrogen compounds, and the depth of its color and the gas samples of the concentration of NO2 is proportional to the determination of the spectrophotometric method. As the NO in the gas sample does not react with the absorbent, so the determination of the total amount of nitrogen oxides must first make the sample through the oxidation tube, NO oxidation into NO2, and then through the absorbent for color development. It can be seen that the sample gas is not measured through the oxidation tube is the NO2 content, measured through the oxidation tube of the total amount of NO2 and NO, the difference between the two is the NO content.
Materials and Instruments
Air Move I. Reagents Caveat 1. The absorbent should be protected from prolonged exposure to the air so that it does not absorb nitrogen oxides in the air and increase the blank value of the reagent. Sunlight can make the absorbent liquid color, therefore, in the sampling, transportation and storage process, should take measures to avoid light. 2. After sampling, if the volume of absorbent decreases significantly, it should be replenished with water to its original volume. 3. chromium trioxide-quartz sand is suitable for use when the air humidity is 30%~70%, and the oxidizing tube should be changed diligently when the humidity is greater than 70%. When the oxidizing tube is found to absorb moisture and turn green, it should be replaced in time. Oxidation tube in the chromium trioxide quartz sand slate will make the sampling system resistance increases, affecting the flow rate, should be replaced. 4. When the absorbing solution is contaminated with chromium trioxide, the solution is yellowish brown and the sample is wasted. 5. Oxidizing agent can also be used acidic potassium permanganate solution, not affected by air humidity, non-toxic, long service life, easy to use for a long time sampling. For more product details, please visit Aladdin Scientific website.
Ice acetic acid P-aminobenzene sulfonic acid Naphthalene ethylenediamine hydrochloride Sodium nitrite
Spectrophotometers Porous glass plate absorber tubes Plugged colorimetric tubes Atmospheric samplers
1. Absorbent solution (color developing solution): weigh 5.0 g of p-aminobenzenesulfonic acid, put it directly into a 1 000 mL brown volumetric flask, add 50 mL of glacial acetic acid and 900 mL of water, cover the stopper and shake gently, when it is dissolved, add 0.05 g of naphthalene ethylenediamine hydrochloride, dissolve it, dilute it with water to the standard line, and then move it to the brown flask. Sealed and stored in the refrigerator can be stored for 3 months. If it shows red color it should be discarded and reconstituted.
2. Absorbent solution: Take 4 volumes of the above absorbent stock solution and mix it with 1 volume of water to obtain the absorbent solution. Preparation before use.3. Oxidizing agent: sieve 20 ~ 40 mesh quartz sand, with (1 + 2) hydrochloric acid solution soaked for a day and night, washed with water to neutral drying. Chromium trioxide and quartz sand according to the mass ratio of 1:20 mixed, add a small amount of water to mix, 105 ℃ drying, drying process should be stirred several times. Produced chromium trioxide - quartz sand should be loose, if stuck together, indicating that too much chromium trioxide, can be appropriate to put some more quartz sand, re-formulation. Will make a good chromium trioxide - quartz sand loaded into the oxidation tube, both ends with skimmed cotton plugged, with latex tubes connected to both ends of the seal made of oxidation tube.4. Sodium Nitrite Standard Stock Solution (CNO2-=100 ug/mL): Weigh 0.1500 g of sodium nitrite ( NaNO2 ) dissolved in water in a desiccator for 24 h. Dissolve in water to a volume of 1,000 mL and transfer to a brown reagent bottle. Store in refrigerator for 3 months.5. Sodium nitrite standard solution (5.0 ug/mL): Pipette 5 mL of the above stock solution into a 100 mL volumetric flask, and then dilute with water. Prepare when ready to use.II. Experimental steps
1. Plotting of standard curves
Take 7 stoppered colorimetric tubes and prepare the standard solution according to Table 1. After each tube was shaken well and kept away from light for 15 min, the absorbance was measured at the wavelength of 540 nm using a 1 cm cuvette with water as the reference, and the regression equation of the standard curve was calculated by the method of least squares:Y=bx+aEq:Y - the difference between the absorbance A of the standard solution and the absorbance A0 of the blank;b - the slope of the regression equation;x - NO2-content, ug;a - regression equation intercept.
2. Sampling and color development
In a porous glass plate pipette, add 5 mL of absorbent solution, connect the inlet to the oxidizing tube with a piece of latex tubing as short as possible, and sample at a flow rate of 0.25 L/min until the absorbent solution is rose-red in color (protection from light should be taken during sampling). After sampling, the sample should be analyzed as soon as possible. Record the temperature and atmospheric pressure at the sampling site.
Table 1 Sodium nitrite standard solution series3. Measurement of samples
After sampling, leave the sample in the dark for 15 min, transfer the sample into a 1 cm cuvette, and determine the absorbance of the blank and the sample according to the method and conditions of the standard curve.
III. Calculation of results
C(NOx) = (A-A0-a) × V/(b × 0.76 × V0)Eq:C (NOx) - Concentration of Nox in the air (in terms of NO2 ), mg/m3;0.76 - coefficient of conversion of NO2 (gas) into NO2- (liquid);V0 - volume of sampling converted to standard, mL;A - absorbance of the sample solution;A0 - reagent blank absorbance;a - regression equation intercept;b - slope of the regression equation.