Which two pollutants are commonly monitored to meet NAAQS requirements?

• A. CO and CH4.
• B. PM2.5 and O3.
• C. Lead and NO2.
• D. SO2 and VOCs.

Answer: (B)

NAAQS compliance relies on monitoring pollutants that have enforceable national standards. Among those, two that are routinely tracked across most networks are PM2.5 and ground-level ozone. PM2.5 refers to fine particulate matter that can penetrate deep into the lungs and contribute to heart and lung disease; measuring its concentration helps determine if the air meets the standard for fine particles. Ozone at ground level forms from reactions of NOx and VOCs in sunlight, and its levels vary with weather and location, so widespread monitoring is essential to protect health and guide controls. The other options aren’t as representative: methane isn’t a NAAQS pollutant, while VOCs aren’t directly regulated by a NAAQS standard (and ozone is the direct monitoring metric tied to those precursors).