This set of Air Pollution Control Multiple Choice Questions & Answers (MCQs) focuses on “Analysis of Air Pollutants – Set 2”.
1. Which method is used most commonly for the detection of nitrogen oxides?
a) Colourimetry
b) Iodometry
c) Turbidimetry
d) Conductometry
View Answer
Explanation: Colourimetry method, specifically the one proposed by Griess-Saltzmann, is used for the detection of nitrogen oxides. This method is specific to nitrogen dioxide but can be used to detect nitric oxide also.
2. Which of the following methods is not used for the continuous analysis of nitrogen oxides (NO, NO2)?
a) Colourimetry
b) Electrochemical method
c) Nondispersive IR devices
d) Chemiluminescent type devices
View Answer
Explanation: Of the given options, only the electrochemical method is not used for the detection of nitrogen oxides. The concentrations of nitrogen dioxide and nitric oxide can be measured separately and then combined for a cumulative.
3. Which of the following devices are preferred for the measurement of nitrogen oxide concentrations?
a) Colourimetry
b) Nondispersive IR spectrophotometry
c) Chemiluminescent type devices
d) Concentration determines the process used
View Answer
Explanation: Among the given options, the chemiluminescent devices are very viable. They are not very expensive when compared to spectrophotometers. These devices are sensitive, and hence, accurate.
4. Which of the following instruments is used to measure the concentration of carbon monoxide?
a) Nondispersive IR spectrophotometry
b) Iodometry devices
c) Chemiluminescent type devices
d) Conductometry devices
View Answer
Explanation: Nondispersive IR spectrophotometry is used to measure carbon monoxide concentration. This continuous method is used most widely for the detection of atmospheric carbon monoxide. These instruments are fast and highly sensitive.
5. What range of CO concentrations can commercial instruments detect?
a) 1 to 100 ppm
b) 25 to 100 ppm
c) 0.1 to 25 ppm
d) 0.1 to 1000 ppm
View Answer
Explanation: Commercial instruments can detect concentrations ranging from 1 ppm to 100 ppm. The range depends on several factors, like operating pressures and path length. Interference can also be a problem, especially vapours.
6. For measurement of stack emissions of CO, which factors are considered for the choice of device?
a) The interference causing materials
b) Desired accuracy degree
c) The cost
d) Portability
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Explanation: Although cost and portability are important factors, they are not deciding factors. The desired accuracy of measurement, as well as, the expected pollutant concentration, are determining factors for the choice of instrument.
7. Other than the NDIR method, which other technique is used for carbon monoxide measurement?
a) Electrochemical method
b) Colourimetry
c) Orsat method
d) Flame photometry
View Answer
Explanation: The Orsat method is a popular method of measurement, which is a wet chemical method. This method is used when the carbon monoxide concentration is higher than 0.2% by volume (2000 ppm).
8. The standard KI method is used to measure the concentration of which gaseous pollutants?
a) Nitrogen dioxide
b) Peroxides
c) Ozone
d) Total oxidants
View Answer
Explanation: The KI method developed by Saltzman is used to measure the net concentration of total oxidants. These oxidants include hydrocarbon peroxides, ozonides, et cetera. The process is primarily manual, but it can be automated as well.
9. Which method is used for the continuous measurement of total oxidants?
a) Colourimetry
b) Mass spectroscopy
c) Standard KI method
d) UV spectrometry
View Answer
Explanation: The colourimetry (also known as Mast and Saunders analysis) method is the preferred method of continuous measurement. The sensitivity of this instrument is less than 0.01 ppm. The detection faces interference from other ambient gases.
10. Which atmospheric gases hinder the measurement of oxidants?
a) Carbon dioxide
b) Nitrogen dioxide
c) Carbon monoxide
d) Nitric oxide
View Answer
Explanation: Nitrogen dioxide and sulphur dioxide interfere in the detection of oxidants. This interference is detected in the standard KI method as well as the colourimetry method. These gases participate in the chemical reaction and result in lower readings.
11. The measurement of hydrocarbon concentration excludes the measurement of methane.
a) True
b) False
View Answer
Explanation: This statement is true because methane is not a hazardous air pollutant. Including the methane concentration is not applicable. Therefore, the measurement is reported on a non-methane basis.
12. Which method is used to measure the concentration of hydrocarbons?
a) Electrochemical method
b) Chemiluminescent type devices
c) Flame ionisation method
d) IR spectrophotometry
View Answer
Explanation: The flame ionisation method is used for the measurement of total hydrocarbons. In this method, the sample is injected into a flame. The flame is created by burning hydrogen in an environment of air or oxygen.
13. What is a disadvantage of using the flame ionisation method for the detection of hydrocarbons?
a) It has a low sensitivity
b) It does not differentiate between different hydrocarbons
c) It is dangerous
d) Its detection range is low
View Answer
Explanation: The flame ionisation method gives the total hydrocarbon concentration. Since the whole sample is injected into the flame, there is no way of differentiating one component from the other.
14. What is the measurement of particulate matter in flue gas based on?
a) Particulate density
b) Opacity of pollutants
c) Density of gas
d) Diameter of the particulate
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Explanation: There are two ways to measure the particulate matter. They can be measured using their mass or their opacity. Opacity measurements are essential because emissions containing particulate matter may be visible once ejected from the stack.
15. Which method is used for the continuous monitoring of emission concentrations of particulate matter?
a) Electrochemical method
b) Flame ionisation method
c) Piezoelectric monitor method
d) IR spectrophotometry
View Answer
Explanation: The piezoelectric method is used for the continuous measurement of particulate emissions. However, the technique gets complicated when scaled for industrial use. This complication makes their application limited.
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