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

A useful shortcut is to remember each analyser by the physical principle its name literally describes, then match by elimination. "Chemiluminescence" literally means light produced by a chemical reaction, which is exactly how the NO analyser works when NO reacts with ozone inside the instrument, so that method belongs to nitrogen dioxide (Q). "Ultraviolet fluorescence" describes a gas absorbing UV energy and re-emitting it as fluorescence, the working principle used for sulphur dioxide (P) analysers. "Non-Dispersive Infra-Red spectroscopy" targets gases with strong infrared absorption bands, which is the classic way to measure carbon monoxide (S), since CO absorbs IR radiation strongly at a specific wavelength. That leaves "beta attenuation," which works only for particulate matter (R), because it measures the reduction in beta-particle count as radiation passes through particulates collected on a filter, a technique that only makes sense for solid particulate matter, not for a gas. Assigning by elimination in this way gives P to (iii), Q to (i), R to (iv), and S to (ii), exactly option (C).

\[\boxed{(P)\text{-(iii)};\ (Q)\text{-(i)};\ (R)\text{-(iv)};\ (S)\text{-(ii)}}\]