The National Institute for Occupational Safety and Health (NIOSH) is engaged in a workplace exposure assessment of cellulose insulation (CI) applicators. Real-time sampling for airborne particulates is conducted during CI application activities with a light scattering aerosol spectrometer designed for real-time particulate measurement with particle size discrimination. Eight channels collect count information for particle sizes greater than 0.75, 1, 2, 3.5, 5, 7.5, 10, and 15 micrometers ( m). Data are collected to monitor the particulates generated by distinct events during CI installation activities in the attic and hopper areas. For each operation, data are integrated for 1 minute (min) and stored sequentially on the Grimm data card over the entire time period. The collected particle count and size information is downloaded to a laptop computer following the completion of the operation. Start and stop times for significant operations are recorded during each sample collection period.