Which of the following is called the secondary air pollutant?
(c) Carbon monoxide
(d) Nitrogen Dioxide
Answer: (b) Ozone is called a secondary air pollutant. Ground-level ozone is a colorless gas that develops just above the earth’s surface and is extremely unpleasant. Because it is generated when two principal pollutants react in sunlight and stagnant air, it is referred to as a “secondary” pollutant. Nitrogen oxides (NOx) and volatile organic compounds (VOCs) are the two main pollutants (VOCs).