The chemistry, aerosol physics, and optical properties of a western coal-fired power plant plume☆

Abstract Data obtained from the airborne measurements in the plume of the Navajo Generating Station (NGS) in June–July and December 1979 as part of the EPA project VISTTA are reported. Source test and airborne data for the ratios SO 2 /NO x , particulates/SO 2 and the size distribution of the primary particles agreed to within the variability of the emissions. NO 2 concentrations in the plume were in agreement with the photostationary steady state relations; there was no evidence for additional oxidant formation at distances up to 115 km. The formation of sulfate and nitric acid was strongly suppressed in the concentrated plume, where ozone is depleted. Sulfate conversions of less than 0.1 % were typically observed for plume ages of 2 to 3 h in the morning sunlight. The highest SO 2 oxidation rates observed in the dilute plume were 0.8%h in the summer between 59 and 89 km in the late morning and 0.2 %/h in the winter between 93 and 108 km in the afternoon. Nitric acid was always observed in the plume and the rate of conversion of NO x to nitric acid was 3 to 10 times the rate of conversion of SO 2 to sulfate. Ammonia concentrations were adequate to neutralize the secondary sulfate, but not to saturate the plume with ammonium nitrate. Particulate nitrates were not observed. New aerosol was reliably detected only in the 0.01 to 0.1 μm size range, which is ineffective at scattering light. Growth of particles larger than 0.1 μm was hard to detect in the presence of the variations in the background aerosol concentration. The emissions which affect the plume visibility are NO x and fly ash, which was predominantly in the 2–7 μm size range. Secondary aerosol formation in the NGS plume can be neglected in visibility models for distances up to 100km, but significant amounts of NO x were removed by oxidation. On the average, extinction due to fly ash and NO 2 were equal for blue light for 7% conversion of NO x to NO 2 , and for green light at 26 % conversion. Fly ash always dominated extinction in the red. Telephotometer sight path flight data were obtained for plume visibility model validation.