How do we measure trace gas pollutants in the atmosphere?

We can measure trace gas pollutants in the atmosphere by using machines or equipments that analysis quantitatively. Examples of these are cyclones, electrostatic precipitator, air bags, venture, absorbers, distillers and many more. They manipulate the properties of these gases in order to extract the pollutants from the clean gas. 

because natural gas is colorless, odorless, and tasteless, distributors add mercaptan (a chemical that smells like sulfur) to give natural gas a distinct unpleasant odor (it smells like rotten eggs). they locate the types of rock that are likely to contain natural gas deposits.

im pretty sure its b