Workers operating aluminum smelting potrooms are at increased risk of asthma and other respiratory conditions, however the etiologic agent(s) have not been determined. Prime candidates for these problems are the acid gases, hydrogen fluoride (HF) and sulfur dioxide (SO2) which are released during particular phases of the smelting operations, producing high transient peaks of exposure. Peak exposures to particulate (including alumina, cryolite and aluminum fluoride) also occur during these operations. These peak exposures may be important factors in producing the observed pulmonary effects. We propose to adapt real-time instruments for monitoring HF and SO2 and non-specific particulate, integrating currently available, electrochemical sensor and light scattering technology and, using these instruments, to monitor exposure in four aluminum smelting operations. Peak exposures will be characterized within specific job tasks and distribution of these exposures will be modeled as a function of smelter technology, location, work task, etc. Monitoring will also be conducted using time-integrating instruments in order to characterize the particle size distribution and to calibrate the direct reading instrument's response. Work observations will be conducted in order to identify the tasks conducted and location of the worker during these monitoring periods and determine the use of respiratory protection. Respirator fit factors will be determined on each subject before and after each monitored period using a controlled negative pressure respirator test system. A set of exposure/dose metrics will be developed to characterize exposure and pulmonary dose during smelter work processes. These metrics will account for the variable exposure distributions and the time-course of exposure. In addition, regional pulmonary deposition of particles and gases, and the effectiveness of respiratory protection will be incorporated into these metrics. The association of the exposure/dose metrics that incorporate peak exposures will be applied to a previously studied inception cohort of potroom workers. Alternative metrics using only average exposures, and the metrics incorporating peak information and pulmonary dose estimates will be compared in order to assess the likelihood that the development of increased bronchial hyper-responsiveness and asthma-like symptoms are associated with acid gas peaks.