Learners discover that their breath contains carbon dioxide, one of the pollutants found in car exhaust. They blow bubbles into water, then use an indicator (bromothymol blue) to see that the water has become acidic, much the same way that rain becomes acidic from pollution in the atmosphere. Instructions are included to make another indicator from cabbage juice which can be substituted in the activity. When learners set up a free account at Kinetic City, they can answer bonus questions at the end of the activity as a quick assessment. As a larger assessment, learners can complete the Smart Attack game after they've completed several activities.