Exposure to ambient particulate matter has been associated with a range of adverse health effects; including: premature mortality, aggravation of existing respiratory conditions, changes to lung tissues and structures, and altered respiratory defense mechanisms. These responses to exposure are a function of the exposure concentration, the duration of the exposure, and the amount absorbed in the body (i.e., dose over time).

As a preventive step against these adverse health effects, the US Environmental Protection Agency (EPA) established a National Ambient Air Quality Standard (NAAQS) for particulate matter. US ambient (NAAQS) and American Council of Government Industrial Hygienists (ACGIH) occupational standards were established to protect the general US population and to provide protection in the workplace environment. Ambient standards were designed to protect populations that included the sick, the elderly, and the very young and would therefore provide a more conservative level of protection for US troops.

The EPA established the first NAAQS for particulate matter in 1971. It targeted the total suspended particulate (TSP) mass per unit volume of air, without regard to the chemical composition of the particles. In 1987, the EPA revised the standard, changing the indicator from TSP to PM10. The EPA decided that PM10 was a better public health indicator than TSP because it targeted particles small enough to enter and deposit in the tracheobronchial region or penetrate deeper in the lung into the pulmonary region (alveolar region where gas exchange occurs) if the particles are small enough (about 10 �m AED or less). The PM10 standard, like the TSP standard, was based on mass without regard to chemical composition.[22]

The 1987 EPA criteria for PM10 is 150 m g/m3 averaged over 24 hours and 50 m g/m3 averaged annually.[23] The data collected in 1991 by the USAEHA shows that the PM10 concentrations at Saudi Arabian and Kuwaiti monitoring stations consistently exceeded the EPA 24-hour criteria of 150 m g/m3 (see Table 1).

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