How can carbon dioxide be considered a pollutant when it is a natural component of air? a. carbon dioxide is considered a pollutant even though it is a natural component of air, because it is harmful to all living organisms. b. carbon dioxide is considered a pollutant when larger concentrations than normal are present in the air as a result of human activity. c. carbon dioxide is considered a pollutant, because it forms harmful chemicals when mixed with other pollutants in the air. d. carbon dioxide cannot be considered a pollutant under any circumstances.