The National Human Activity Pattern Survey (NHAPS): a resource for assessing exposure to environmental pollutants

Because human activities impact the timing, location, and degree of polluta nt exposure, they play a key role in explaining exposure variation. This fa ct has motivated the collection of activity pattern data for their specific use in exposure assessments. The largest of these recent efforts is the Na tional Human Activity Pattern Survey (NHAPS), a 2-year probability-based te lephone survey (n = 9386) of exposure-related human activities in the Unite d States (U.S.) sponsored by the U.S. Environmental Protection Agency (EPA) . The primary purpose of NHAPS was to provide comprehensive and current exp osure information over broad geographical and temporal scales, particularly for use in probabilistic population exposure models. NHAPS was conducted o n a virtually daily basis from late September 1992 through September 1994 b y the University of Maryland's Survey Research Center using a computer-assi sted telephone interview instrument (CATI) to collect 24-h retrospective di aries and answers to a number of personal and exposure-related questions fr om each respondent. The resulting diary records contain beginning and endin g times for each distinct combination of location and activity occurring on the diary day (i.e., each microenvironment). Between 340 and 1713 responde nts of all ages were interviewed in each of the 10 EPA regions across the 4 8 contiguous states. Interviews were completed in 63% of the households con tacted. NHAPS respondents reported spending an average of 87% of their time in enclosed buildings and about 6% of their time in enclosed vehicles. The se proportions are fairly constant across the various regions of the U.S. a nd Canada and for the California population between the late 1980s, when th e California Air Resources Board (CARB) sponsored a state-wide activity pat tern study, and the mid-1990s, when NHAPS was conducted. However, the numbe r of people exposed to environmental tobacco smoke (ETS) in California seem s to have decreased over the same time period, where exposure is determined by the reported time spent with a smoker. In both California and the entir e nation, the most time spent exposed to ETS was reported to take place in residential locations.