Air pollution can ruin your outdoor plans

Air pollution is measured with the Air Quality Index, or AQI.

The lower the AQI, the cleaner the air is. However, if you are outside when the AQI is over 100, it’s about the same as breathing in exhaust from a car all day! Things that cause poor air quality are forest fires and cities with lots of car traffic. If the AQI is higher than 100 you shouldn’t spend too much time outside.
Carbon dioxide in the air can be both good and bad
When humans and animals breathe, we give off an odorless gas called carbon dioxide, or CO2. Plants use this gas, along with sunlight, to make food—a process called photosynthesis. In this process, plants give off oxygen, too! However, large amounts of CO2 are also produced when cars and power plants burn coal, oil, and gasoline. CO2 is also the most important contributor to human-caused global warming.
Source – Climate.NASA.GOV