THE MEASUREMENT AND DECOMPOSITION OF TOTAL EXPOSURE USING THE TOTAL-ISOLATED-BY-MICROENVIRONMENT-EXPOSURE (TIME) MONITOR

Exposure to pollutants is either measured by direct methods, or estima ted by indirect methods. Direct methods use personal sampling devices that measure exposure across all microenvironments in which individual s spend their time. Indirect methods of exposure estimation involve pa rallel, independent measurements of pollutant concentrations in microe nvironments, and activity patterns of subjects. Indirect methods combi ne these two independent measurements. This paper describes a new, hig hly compact and lightweight monitor that directly measures personal ex posure resolved into four microenvironments. The device is the ''Total -Isolated-by-Microenvironment-Exposure (TIME)'' monitor. The monitor c an identify electronically a subject's microenvironment and measure th e time and the concentrations of air pollutants while the subject is i n that microenvironment. A sensor electronically directs the air it sa mples from a microenvironment to a sampling collector (sorbent tube) u niquely associated with each of the four microenvironments: indoors-no noccupational, indoors occupational, in-transit, and outdoors. Over a period of 24-hours, the TIME monitor measures exposures in the four mi croenvironments and, by adding the concentrations for the four compone nts, the monitor provides a measure of total daily exposure. The TIME monitor was used to conduct a limited field test in which exposures to target Volatile Organic Compounds (VOCs) listed in the EPA TO-14 meth od were measured. Results from this brief test indicate that the activ ity patterns recorded electronically are within six minutes of careful ly logged activity patterns. Microenvironmental exposure values to VOC s compare favorably with published information obtained with more comp lex instrumentation. Results verify the importance of having accurate time activity data and microenvironmental concentrations to obtain an accurate estimate of total exposure using conventional methods of deco mposing total exposure into its microenvironmental exposure components .