Which of the following best lists the primary air pollutants associated with coal combustion?

• A. CO2, sulfur oxides, nitrogen oxides, and mercury
• B. Methane, ammonia, chlorine, and ozone
• C. CO2, sulfur oxides, nitrogen oxides, and particulate matter
• D. Water vapor, carbon dioxide, nitrogen, oxygen

Answer: (C)

Coal-fired combustion releases several pollutants directly into the air, and the most significant ones are carbon dioxide, sulfur oxides, nitrogen oxides, and particulate matter.

Carbon dioxide is produced whenever carbon in coal is burned and is the largest greenhouse gas emitted from fossil fuels, contributing to climate change. Sulfur in coal converts to sulfur oxides during combustion, which are mainly sulfur dioxide; these gases lead to acid rain and respiratory issues and are a major air-quality concern. High-temperature burning also forms nitrogen oxides, which contribute to smog and ozone formation and have health effects. Particulate matter comprises tiny particles like fly ash and soot that can penetrate deeply into the lungs and bloodstream, posing serious health risks and environmental damage.

Mercury is present in coal and is a toxic pollutant, but it’s usually addressed as a separate, specialized emission issue rather than one of the primary air pollutants category typically emphasized for coal combustion. The other listed substances—methane, ammonia, chlorine, ozone; water vapor, carbon dioxide, nitrogen, oxygen—either aren’t emitted in the same dominant way by coal burning or aren’t pollutants released directly in the same sense.