Concentrations of VOCs in New Houses
Samples for VOCs and aldehydes were collected in the 4 new manufactured houses over 2 to 9.5 months following installation and in the 7 new site-built houses 1 to 2 months after their completion. The house HVAC systems were operated for at least the day prior to VOC sample collection. Ventilation rates were measured by tracer-gas decay concurrently with air sample collection. The multisorbent VOC samples were analyzed by thermal desorption GC/MS. The aldehyde samples collected on treated cartridges were solvent eluted and analyzed by HPLC. The geometric mean (GM) concentrations in ppb, geometric standard deviations and concentration ranges for 28 predominant VOCs in the manufactured and site-built houses are presented and compared in Table 8. The GM concentrations for all 54 compounds are categorized by concentration range in Table 9.

The predominant VOCs in the two house types included alpha-pinene, ethylene glycol, formaldehyde, acetaldehyde, hexanal and acetic acid. The GM formaldehyde concentration for the 4 manufactured houses was less than one-half the historical value for manufactured houses and all of the values were less than 50 ppb, a concentration guideline established in California ( http://www.arb.ca.gov/research/indoor/formald.htm). The concentrations in the 7 site-built houses were similar with only two values somewhat in excess of 50 ppb. The similarity between the manufactured and site-built houses may have been due to the general similarity of their interior construction practices and materials.

VOCs in New Houses That are of Concern with Respect to Odor and Sensory Irritation
For some chemical classes of VOCs, odor serves as a warning mechanism. Therefore, odor thresholds, for which there are substantial data, may serve as general exposure guidelines. In addition, it is desirable to limit odors from interior materials as the perception of odor may adversely impact people's satisfaction with their indoor environment. A number of commonly occurring alcohols, aldehydes and carboxylic acids produce objectionable odors at relatively low concentrations. Maximum VOC concentrations in the houses are compared to odor thresholds in Table 10. The concentrations of acetic acid and the aldehydes, hexanal, heptanal, octanal and nonanal approached or exceeded their respective odor thresholds.

Many VOCs are known to produce sensory irritation to the eyes and upper respiratory tract. Most of the data and guidance with respect to chemical irritants comes from industrial work environments. A number of the Threshold Limit Values (TLVs) developed for occupational exposures by the American Conference of Governmental Industrial Hygienists are based on irritant effects (http://www.acgih.org/TLV/). There is no clear guidance on how to adjust industrial TLVs based on irritancy to make them applicable to the general population. However, others have adopted an uncertainty factor of 40 to protect more sensitive populations. Comparison of maximum VOC concentrations in the houses with TLVs adjusted by a factor of 40 shows that formaldehyde concentrations consistently exceeded the guide value and that acetic acid concentrations approached and occasionally exceeded the guide value (Table 10).