Q. Which of the following is a secondary air pollutant?
a. Acid rain
d. Dust particles
Secondary pollutants include ozone, which is formed when hydrocarbons (HC) and nitrogen oxides (NOx) combine in the presence of sunlight.
Whereas Primary pollutant is those pollutants that are directly emitted from their sources, like CO2, CO, SO2 as these gases are directly emitted from the burning of fossil fuels.
Acid rain, which is formed when sulfur dioxide or nitrogen oxides react with water, sulfuric acid, etc.
Hence, Acid rain is a secondary air pollutant.