Step 1: Differentiate primary and secondary air pollutants.
Primary pollutants: Directly emitted into the atmosphere from sources such as vehicles, industries, or natural processes. Examples include \( \text{CO}_2 \), \( \text{SO}_2 \), and \( \text{NO}_x \).
Secondary pollutants: Formed by the chemical reactions of primary pollutants in the atmosphere. Examples include \( \text{O}_3 \), \( \text{HNO}_3 \), and \( \text{H}_2\text{SO}_4 \).
Step 2: Analyze the options. \( \text{O}_3 \): A secondary pollutant formed by the photochemical reaction of \( \text{NO}_x \) and volatile organic compounds (VOCs). \( \text{HNO}_3 \): A secondary pollutant formed by the reaction of \( \text{NO}_x \) with water vapor. \( \text{CO}_2 \): A primary pollutant directly emitted from combustion processes. \( \text{H}_2\text{SO}_4 \): A secondary pollutant formed by the oxidation of \( \text{SO}_2 \) in the atmosphere.
Length of the streets, in km, are shown on the network. The minimum distance travelled by the sweeping machine for completing the job of sweeping all the streets is ________ km. (rounded off to nearest integer)