IV. PARTICULATE MATTER AIR QUALITY STANDARDS
As a preventive step against potential adverse health effects, the US Environmental Protection Agency (EPA) established a National Ambient Air Quality Standard (NAAQS) for PM. The US ambient standards and the American Council of Government Industrial Hygienists occupational standards were designed to establish limits on levels of specific pollutants in the ambient environment and in the workplace. Ambient standards were designed to protect the sick, the elderly, and the very young and therefore provide a higher level of protection when applied to exposure scenarios involving US servicemembers who are generally young, healthy adults.
In 1987, the EPA revised the NAAQS for particulate matter, originally issued in 1971 as "total suspended particulate" standards, to focus on human health effects associated with exposure to ambient PM less than 10 microns that can settle in thoracic (tracheobronchial and alveolar) portions of the lower respiratory tract. Reevaluation of newly available scientific information, as presented in "Air Quality Criteria for Particulate Matter," published in 1996, provided key scientific bases for particulate matter NAAQS decisions published in July 1997. The PM10 NAAQS established by the EPA in 1987 (150 mg/m3, 24-h; 50 mg/m3, annual average) were retained and new standards for particles � 2.5 mm (PM2.5) were established (65 mg/m3, 24-h; 15 mg/m3, annual average).
The data collected in 1991 by the USAEHA show that the PM10 average 24-hour concentrations at Saudi Arabian and Kuwaiti monitoring stations consistently exceeded the EPA 24-hour standard of 150 mg/m3 (see Table 1).
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