Introduction
Smog is a combination of the term’s "smoke" and "fog," which are two separate concepts. When nitrogen oxides and volatile organic compounds mix in the atmosphere under the influence of sunlight, smog is a form of air pollution that develops (Concord, 2015). The overwhelming majority of smog that occurs in cities is of this type, known as photochemical smog. The World Health Organization states that particulate matter, carbon monoxide, nitrogen oxides, sulphur dioxide, and ozone are the air pollutants that have the greatest impact on public health (World Health Organization, 2006). Due to human activities, gasoline used in diesel-powered cars, industrial facilities, and heating processes primarily emit these pollutants (Penkova, 2016).
| Air Quality Index Levels of Health Concern | Meaning |
| Good | Air quality is considered satisfactory, and air pollution poses little or no risk. |
| Moderate | Air quality is acceptable; however,for some pollutants there may be a moderate health concern for a very small number of people who are unusually sensitive to air pollution. |
| Unhealthy for Sensitive Groups | Members of sensitive groups may experience health effects. The general public is not likely to be affected. |
| Unhealthy | Everyone may begin to experience health effect; members of sensitive groups may experience more serious health effects. |
| Very Unhealthy | Health alert: everyone may experience more serious health effects. |
| Hazardous | Health warnings of emergency conditions. The entire population is more likely to be affected. |