Air quality is measured by the composition of specific pollutants at a particular location & time. Six pollutants are measured: sulfur dioxide, nitrogen oxides, particulate matter, carbon monoxide, ozone & lead. Hign concentrations of any of these cause air pollution or poor air quality.
Poor air quality can result in immediate irritations to breathing & eyes and also cause long-term health problems including cancer, birth defects, and brain, nerve & respiratory damage. If the air quality is extremely poor, it could lead to serious injury and even death. For more info, including day-to-day Air Quality Index (AQI) data, refer to: