Air emissions from major industry—identify the common pollutant Which pollutant is commonly emitted from metallurgical smelters, thermal power plants, and cement plants, and is a key target for flue-gas desulfurization?

Introduction / Context:
Sulfur dioxide is one of the most regulated air pollutants due to its role in acid rain formation, particulate sulfate generation, and adverse health impacts. Large stationary sources—especially coal-fired power plants, sulfide-ore smelters, and certain cement kilns—are classic emitters of SO2 unless equipped with control systems.

Given Data / Assumptions:

• Fuel sulfur or sulfide minerals present in the feed contribute to SO2 during combustion/roasting.
• Smelters process sulfide ores (e.g., Cu, Ni, Pb), releasing SO2 during oxidation.
• Thermal power plants burning sulfur-bearing coal or oil emit SO2 without scrubbing.
• Cement plants can emit SO2 from fuel and raw-meal sulfur compounds.

Concept / Approach:
Link the sulfur-containing inputs to the formation of SO2 in high-temperature processes. Among the options, SO2 is the broadest common denominator across the three listed industries. NOx is also produced in combustion, but smelters’ defining pollutant is typically SO2 from sulfide oxidation. Mercury and fluorine emissions are more site-specific.

Step-by-Step Solution:

Verification / Alternative check:
Emission inventories consistently rank SO2 as a primary pollutant from these sectors without abatement; FGD, sorbent injection, and low-sulfur fuels target SO2 reductions.

Why Other Options Are Wrong:

• NOx: common in combustion but not a hallmark of sulfide-ore smelters like SO2.
• Hg: emitted mainly from certain coals; not universally high in smelters/cement.
• F: notable for some aluminum/cement processes, but not common to all three sectors.

Common Pitfalls:
Overgeneralizing NOx to all high-temperature processes; smelter emissions are characteristically sulfur-driven.

Final Answer:
Sulfur dioxide (SO2)