Breathing Zone Exposure Assessment - Aerosols: Measurement, Dosimetry, and Health Effects - page 40

Inlet

Pump in
waistpack

Inlets

Pump

(a)

(b)

FIGURE 2.2 BZ inlets fastened to (a) a low-lint vest that can be worn over clothing and (b) a shoulder strap
located within the BZ rather than on the more distant waist pack.

reduction approaches include utilizing a waist pack with the inlet mounted on the front, a back-
pack with the inlet mounted on the side, or for those participants who have physical disabilities, a
luggage-cart-mounted personal exposure system. Examples of these are shown in Figure 2.3.
Validated exposure models are the most obvious approach to developing exposure databases
with minimal cost and no burden applied to the target cohorts. Such models for sized particles in
residential settings (e.g., Ott et al., 2000; Burke et al., 2001) are becoming more widely applied and
have been shown to be acceptable predictors of at least the IQR for cohort exposure distributions.
Rodes et al. (2010) reviewed the distributions of personal exposures to ambient ixed-site PM 2.5 data
and noted that the personal exposures at times were two or more times higher than the ambient data
from a combination of SHS (see Section 2.2.2.2) and personal activity cloud sources.

2.4 APPLICATIONS

2.4.1 g eneral
The most common application of BZ personal exposures assessments is to determine the distribu-
tions of exposure as related to a deined PEL. This requires that the methodologies be as accurate
and representative of the true BZ concentrations. If the inlet cannot physically be placed continu-
ously in the subject's BZ (e.g., small children), additional information is needed to subsequently
allow any needed adjustment induced by the separation distance. As noted previously, gases and
ine particles (<∼2.5 μm) may be uniformly distributed in the sampled air. In this case, personal
measurements made by all the approaches given in Table 2.3 may provide statistically equivalent
results. Particles larger than ∼2.5 μm, however, may exhibit signiicant microenvironmental con-
centration gradients that would result in detectible biases between inlet locations. Resuspended
clothing dust and body dander inadvertently collected by the inlet may provide samples that are
not representative of the air in the BZ. Utilizing a (low-lint) sampling vest can reduce clothing
resuspension problems.
Not all personal exposure studies are conducted to estimate actual exposure levels. While occu-
pational BZ measurements are most often collected to make assessments relative to PELs, nonoc-
cupational studies are often conducted to determine how well personal exposures associate with a
dose or adverse health effect. In the case of associative studies, the absolute values are not nearly as