Inhalation exposure
Inhalation is a major route of exposure that occurs when an individual breathes in polluted air which enters the respiratory tract. Identification of the pollutant uptake by the respiratory system can determine how the resulting exposure contributes to the dose. In this way, the mechanism of pollutant uptake by the respiratory system can be used to predict potential health impacts within the human population.
Exposure is commonly understood to be the concentration of the airborne pollutant in the air at the mouth and nose boundary. Outdoor concentrations are often measured at fixed sites or estimated with models. The fraction of this ambient concentration that is inhaled by a person depends mainly on their location (indoor or outdoor), distance to pollution sources and their minute ventilation. Traditionally exposure is estimated based on outdoor concentrations at the residential address. Trips to other locations and physical activity level are mostly neglected although some recent studies have attempted to use portable and wearable sensors.
Intake dose is the mass of the pollutant that crosses the contact boundary and is inhaled by the individual. Some of this pollutant is exhaled, and the fraction that is absorbed by the respiratory system is known as the absorbed dose. A portion of the pollutant may also be expelled by sneezing, coughing, spitting, or swallowing. The remaining pollutant that is transported through the liquid layer, making contact with the respiratory tract tissues is the fraction of bioavailability, called the effective dose.
In 1970, the Clean Air Act Amendments set six criteria air pollutants which are updated periodically by the National Air Quality Standards (NAAQS) and the U.S Environmental Protection Agency (USEPA). The six criteria pollutants were identified based on scientific knowledge of health effects caused by the pollutants. The six criteria are the following: particulate matter (PM), nitrogen oxide NO
2, ozone O
3, sulfur dioxide SO
2, carbon monoxide (CO), and nonmethane hydrocarbons (NHMC). Particulate matter (PM) is divided into two sizes, PM10 which is called inhalable PM, and PM2.5, which is called fine PM.
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