Ozone, a gas that forms in the atmosphere when three atoms are combined through a series of chemical reactions triggered by sunlight, is a major component of smog.
Good up high: "the ozone layer"
There is a natural layer of ozone high in the atmosphere that is created and destroyed at a constant rate by sunlight.
The ozone layer protects us from too much sunlight preventing skin cancer, cataracts, and impaired immune systems.
Bad nearby: smog
Ozone is also formed near the ground from chemical reactions between volatile organic compounds (VOCs) and nitrogen oxides (NOx) in the presence of sunlight.
Major sources of VOCs and NOx are motor vehicle exhaust, power plant emissions, natural gas operations, and chemical solvents.
Ozone and its precursors can be carried far distances by the wind.
What about global warming?
Ozone is a heat-trapping gas that contributes to global warming. Ozone is responsible for ~10% of the warming that we are experiencing today. Hot weather also speeds up reactions, creating more ozone.
Even with the weak standards we have now, 4 in 10 people in the U.S. live in areas that exceed national standards for smog pollution.
Smog pollution is unhealthy and dangerous. It irritates airways, causing burning sensation, coughing, wheezing, shortness of breath, and lung infections. It is linked to asthma, premature mortality, heart failure, lung failure, and increased hospital and emergency room admissions.