Project at a Glance
Title: Impact of improved emissions characterization for nitrogen-containing air pollutants for the South Coast Air Basin.
Principal Investigator / Author(s): Harley, Robert A
Contractor: UC Berkeley
Contract Number: 93-310
Research Program Area: Atmospheric Processes
Topic Areas: Chemistry & Reactivity, Modeling
Nitrogen-containing air pollutants contribute to many of California's air quality problems. The impact of improved characterization of emissions of oxides of nitrogen and ammonia was studied using the CIT airshed model applied to the August 27-29, 1987, intensive monitoring period from the Southern California Air Quality Study. Direct NO2 and nitrous acid emissions at levels between 0-10% and 0-3%, respectively, were used to examine the influence of NOx emission speciation. A 50% reduction in total NOx mass emissions was used to compare the importance of mass emissions and emission speciation. A new NH3 emission inventory developed for the South Coast Air Basin was used in this study.
Model predictions matched the spatial and temporal distribution of observed concentrations of O3, NO2, PAN, HNO3 and fine particle nitrate. Predicted pollutant concentrations were much more sensitive to NOx mass emissions than to NOx speciation. Daytime NO2 concentrations were governed by the rate of conversion of NO to NO2 in the atmosphere, not by direct NO2 emissions. Nighttime NO2 and nitrous acid concentrations were sensitive to NOx speciation. Reducing NOx emissions led to significant reductions in concentrations of NO2, nitric acid, and fine particle nitrate, whereas predicted ozone and PAN concentrations increased.
Direct emissions of NO2 and nitrous acid appear to be at the low end (i.e., close to zero) of the ranges studied here. Heterogeneous conversion of NOx is likely to be the main source of nitrous acid in the atmosphere.
To support modeling and control strategy development for nitrogenous air pollutants, improvements are needed to the ammonia emission inventory. Continuing shifts in agricultural activities within the South Coast Air Basin need to be tracked, the diurnal variation profiles or ammonia emissions need to be improved and new measurements of ammonia emissions from cattle and poultry farms are needed.
For questions regarding research reports, contact: Heather Choi at (916) 322-3893
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