Question

Which ONE of the following options CORRECTLY matches the Criteria Air Pollutants with measurement methods used in Continuous Ambient Air Quality Monitoring Stations (CAAQMS) operated by Central Pollution Control Board (CPCB) given in the table?

Criteria Air Pollutants	Measurement Methods
(P) Sulphur Dioxide (SO2, in µg/m3)	(i) Chemiluminescence
(Q) Nitrogen Dioxide (NO2, in µg/m3)	(ii) Non Dispersive Infra Red (NDIR) spectroscopy
(R) Particulate Matter (PM2.5, in µg/m3)	(iii) Ultraviolet fluorescence
(S) Carbon Monoxide (CO, in mg/m3)	(iv) Beta attenuation

• A. (P) - (i); (Q) - (ii); (R) - (iii); (S) - (iv)
• B. (P) - (iv); (Q) - (iii); (R) - (ii); (S) - (i)
• C. (P) - (iii); (Q) - (i); (R) - (iv); (S) - (ii)
• D. (P) - (ii); (Q) - (iii); (R) - (i); (S) - (iv)

Hint:

Match each pollutant to the physical principle in its instrument name: fluorescence for SO2, chemiluminescence for NO2, beta attenuation for particulates, and NDIR for CO.

Answer 1

The Correct Option is C

Step 1: Recall the standard reference methods CPCB uses for each criteria pollutant in CAAQMS. Continuous Ambient Air Quality Monitoring Stations measure each criteria pollutant with a technique matched to its chemical behaviour.

Step 2: Match Sulphur Dioxide (P). SO2 is commonly measured by the Ultraviolet (UV) fluorescence method, in which SO2 molecules absorb UV light and re-emit fluorescent light proportional to concentration. This corresponds to (iii).

Step 3: Match Nitrogen Dioxide (Q). NO2/NOx is measured by the chemiluminescence method, based on the light emitted when NO reacts with ozone in the analyser; this corresponds to (i).

Step 4: Match Particulate Matter (R). PM2.5 mass concentration is measured continuously using the beta attenuation method, which relates the attenuation of beta radiation passing through particulate collected on a filter tape to the particulate mass; this corresponds to (iv).

Step 5: Match Carbon Monoxide (S). CO is measured using Non-Dispersive Infra-Red (NDIR) spectroscopy, which detects the characteristic infrared absorption of CO gas; this corresponds to (ii).

Step 6: Assemble and conclude. The correct matching is (P)-(iii), (Q)-(i), (R)-(iv), (S)-(ii), which is option (C). The other options mismatch at least one pair, for instance option (A) wrongly pairs SO2 with chemiluminescence, which is actually the NO2 method.