Nitric acid loss rates measured in power plant plumes

Measurements of HNO₃, NO_x, NO_y, 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 NO_x 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.