Which common air pollutant does not typically cause vegetation damage (i.e., is not phytotoxic at ambient urban concentrations)?

Introduction / Context:
Many gaseous air pollutants injure crops and trees by disrupting photosynthesis, damaging leaf tissues, or altering plant metabolism. However, not every common pollutant is strongly phytotoxic at concentrations typically found in ambient air around cities and highways.

Given Data / Assumptions:

• The question asks for the pollutant that does not harm vegetation under usual ambient exposures.
• Consider well-known phytotoxic agents (ozone, SO2, HF, NOx) versus relatively non-phytotoxic gases like CO.
• Context is general urban/industrial air, not acute spill conditions.

Concept / Approach:
Phytotoxicity depends on reactivity and plant uptake. Ozone is a powerful oxidant causing stippling and necrosis. SO2 forms acidic species in leaf tissues. Fluorides are notorious for leaf-tip burn at very low concentrations. Some herbicides (weed killers) drifting off-target cause direct injury. By contrast, carbon monoxide (CO) is relatively unreactive in plant biochemical pathways and at ambient levels is not a typical cause of vegetation damage.

Step-by-Step Solution:

Verification / Alternative check:
Standard environmental texts consistently implicate ozone, SO2, HF, and some NOx as phytotoxic; CO rarely appears on lists of vegetation-damaging pollutants at ambient concentrations.

Why Other Options Are Wrong:

Common Pitfalls:
Assuming all air pollutants harm plants equally; ignoring that CO’s major risk is to humans (carboxyhemoglobin), not to vegetation at ambient levels.

Final Answer:
Carbon monoxide