Indoor and outdoor air pollution monitoring may indicate potential human exposure to air contaminants. Individual and population exposures to air contaminants depend upon many factors including time spent outdoors and indoors, permeability of housing structures, and mobility within a community. In this report, we illustrate an approach for using long-term air monitoring to establish patterns or changes of environmental exposures, improve validity and representativeness of data, and prevent exposure misclassification. Long-term air monitoring for hydrogen sulfide (H2S) at 14 Dakota City, Nebraska, residences identified differences in area-wide concentration levels, geographic locations, and seasonal exposures. Air data for 1999 indicated that Dakota City residents were repeatedly exposed, both indoors and outdoors, to moderate levels (>or=90 parts per billion [ppb]) of H2S. Using GIS modeling and kriging, we produced a geographic gradient of exposure estimate or map for ambient H2S. These findings formed the basis for designing two health investigations for this community.