In 1985, the American Conference of Governmental Industrial Hygienists (ACGIH) recommended particle size-selective sampling in setting threshold limit values for occupational exposures. Since particles must generally become deposited to exert biological effects, these conventions, based on regional exposure (i.e., particles penetrating into a region of the respiratory tract), are conservative by design in that they overestimate the amount of inhaled material that becomes deposited and thereby available to induce an effect. These criteria were specifically developed for workplace atmospheres. Relative to total airborne particles, the particle size having 50% penetration for the thoracic and respirable fractions are 10 μm and 4.0 μm (all particle sizes are aerodynamic diameter unless expressed otherwise), respectively.
The above definitions are stated in terms of a mass fraction. Respirable fraction – the mass fraction of inhaled particles penetrating to the unciliated airways.Thoracic fraction – the mass fraction of inhaled particles penetrating beyond the larynx.Extrathoracic fraction – the mass fraction of inhaled particles failing to penetrate beyond the larynx.Inhalable fraction – the mass fraction of total airborne particles which is inhaled through the nose and mouth.Specific definitions used herein, adopted from the European Committee for Standardization (CEN), are : Most sampling conventions have been defined in terms of particle penetration into respiratory regions rather than the expected particle deposition or dose to regions. Size-selective sampling is intended to help discern the amount of aerosol expected to be available for deposition in a region. The human respiratory tract can be divided into three main regions based on size, structure, and function, namely, the head, tracheobronchial region (also known as the conducting airways), and the gas-exchange region (also known as the parenchymal, alveolar, or pulmonary) region. If an environmentally or occupationally related particle is recognized to only affect the gas-exchange region of the lung, then a sampling strategy that only collects the respirable fraction of airborne PM is preferable to sampling total suspended particulate (TSP) or the thoracic fraction. The concept of size-selective particle sampling has been employed as a means for effectively sampling the particle sizes associated with specific pathologic outcomes (e.g., the respirable fraction with parenchymal disease). Sampling the total air concentration of particulate matter (PM) provides a crude estimate of exposure that may not correlate with observed health effects if the risk is associated only with those particles that may enter the thorax or penetrate beyond the ciliated airways. For example, Morgan concluded that respirable dusts likely caused pneumoconiosis and silicosis in coal miners, whereas a larger size fraction caused bronchitis and obstructive changes in pulmonary function.
To know more about Air Quality and Pollution, check the wikipedia Air Quality topic or the airnow guide to Air Quality and Your Health.įor very useful health advices of Beijing Doctor Richard Saint Cyr MD, check blog.It has long been recognized that the regional pattern of particle deposition in the respiratory tract affects the pathogenic potential of inhaled aerosols. Health alert: everyone may experience more serious health effectsĮveryone should avoid all outdoor exertion The entire population is more likely to be affected.Īctive children and adults, and people with respiratory disease, such as asthma, should avoid all outdoor exertion everyone else, especially children, should limit outdoor exertion.
The general public is not likely to be affected.Įveryone may begin to experience health effects members of sensitive groups may experience more serious health effectsĪctive children and adults, and people with respiratory disease, such as asthma, should avoid prolonged outdoor exertion everyone else, especially children, should limit prolonged outdoor exertion Members of sensitive groups may experience health effects. Air quality is considered satisfactory, and air pollution poses little or no riskĪir 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.Īctive children and adults, and people with respiratory disease, such as asthma, should limit prolonged outdoor exertion.