A chemical compound is substance that is made up of similar molecules made of atoms from different elements tied together with chemical bonds. A mixture is a combination of 2 or more substances. Water, Hydrogen Chloride, and Carbon Dioxide are chemical compounds while Air is a mixture.
Measure CO2 Levels from around the town to see if the ratio of Oxygen to CO2 is irregular. It's also important to take in factor how much CO2 intake the plantation around them is so you can see what the entire amount is.