A critical flow device for accurate PM10 sampling and correct indication of PM10 dosage to the thoracic region of the respiratory tract.

A state-of-the-art flow controller is presented that maintains constant volume flow at ambient conditions. It utilizes the concept of critical flow and is extremely simple in design. It is insensitive to pressure changes; the flow varies only with the square root of ambient absolute temperature, a very small correction that, except under extreme circumstances, can probably be ignored. Both theory and field data are presented. Included is a discussion of the present practice in use by the U.S. EPA to convert the sampled ambient volume to EPA reference conditions (298 K, 101.3 kPa). The intent of size selective ambient monitoring is to mimic tracheobronchial deposition to provide an indicator of particulate matter dosage to the thoracic region of the respiratory tract. Below 2400 m humans breathe at essentially constant volume, where this volume is expressed at ambient pressure and body temperature (37°C). Thus, to simulate dosage to the respiratory tract with an air sampler, we must sample at constant volu...