Carbon monoxide is a harmful gas with no color or smell that comes from burning fuel. On high-pollution days, this invisible gas builds up near the ground. Cities like Phoenix track pollution readings alongside daily weather forecasts because weather and pollution levels shift together — sometimes dramatically. You collect temperature, wind speed, barometric pressure, carbon monoxide, particulates, and ozone readings each day, then graph them all on the same chart. Comparing those graphs reveals which weather conditions line up with the worst air quality days.

Carbon monoxide is a colorless, odorless gas that forms whenever fuel burns incompletely — including inside a car engine. To see how much engine age matters, you measure exhaust emissions from four cars of the same make and model: new, 5 years, 10 years, and 20 years old. Each car runs for 20 minutes with a carbon monoxide detector placed 20 centimeters from the exhaust pipe. You test each car twice, once in a closed garage and once in open air. The 20-year-old car produced the highest readings; the new car produced the lowest. Levels were higher in the closed garage for every car — a clear demonstration of how quickly this invisible gas accumulates when ventilation is cut off.