Measurements of HNO3, NOx, NOy, and CO2 in the plumes from electric utility power plants located in eastern Texas are used to determine the HNO3 loss rates in the planetary boundary layer during plume transport. These 1 Hz measurements were obtained from the National Center for Atmospheric Research Electra aircraft flying on clear afternoons in a well-mixed planetary boundary layer during the Texas Air Quality Study in August and September of 2000. The analysis uses data obtained in 48 crosswind transects of plumes from seven different power plants on six flight days. The NOx lifetime was found to vary from 1.3 to 3.1 hours in these plumes, indicating that the measurements were obtained during periods of rapid photochemical activity. The HNO3 loss rate was 0.45 ¿ 0.21 hour-1 in power plant plumes that were advected over rural regions. Particle size distributions measured in the plumes indicated that gas phase HNO3 was not lost to particle formation. Meteorological effects and land use were also investigated as possible causes for the observed HNO3 loss rates, which were insensitive to the land cover and measured wind speeds and boundary layer heights. The HNO3 loss rate measured in most plumes was more than 4 times greater than what is calculated from deposition velocities and the measured boundary layer height.