Abstract:
Ambient air has particles of different sizes ranging from a few nanometers to several tens of micrometers and amongst these, particles below 10m in diameter (PM10) have the potential to reach and be deposited in the alveoli, while those greater than 10m are removed from proximal airways by mucociliary activity. Studies have suggested an inverse relationship between particle size and total lung deposition (Salvi and Holgate, 1999). Thus, the small sized particles (PM10 and PM2.5) deposit in large numbers in lungs, overwhelming the lung clearance mechanisms and thus increasing the retention. As a strong association between inhaled PM and harmful respiratory effects has been established through various epidemiological and toxicological studies, the EPA Office of Air Quality Planning and Standards (OAQPS) has set National Ambient Air Quality Standards for PM, and all six criteria air pollutants (carbon monoxide, nitrogen dioxide, ozone, lead, PM10, PM2.5, and sulfur dioxide). The standards for PM10 are 50mg/m3 (annual arithmetic mean) and 150mg/m3 (24 hour average) (US EPA, 1990).
A nationwide survey of particulate matter (PM) concentration trends show that the concentration of PM in most areas of the country have been below the level of the annual PM10 standard (50 mg/m3) since 1999. Though the average concentration levels differed among sites, with higher levels at urban and suburban sites, overall nationwide trend showed a decline (US EPA, 2001). In spite of this trend, selected populations, such as the elderly, are still being adversely affected by ambient PM as shown in the mortality and morbidity studies cited below.
Taken from the beginning of thesis.