Environmental Engineering Reference
In-Depth Information
2.3 Nonlinear Formation of Ozone in Power Plant
Plumes in Texas
Wei Zhou and Daniel S. Cohan
Department of Civil and Environmental Engineering, Rice University, Houston, TX 77005,
USA
Abstract
Six Texas power plants are simulated in a photochemical model with
higher-order direct sensitivity analysis to investigate the nonlinear ozone formation
of power plant plumes. Power plants with largest NO
x
emissions had the largest
spatial extent of ozone impact. Ozone production tended to occur sooner in small
NO
x
plumes, but overall ozone production efficiency was similar
for plumes.
Ozone formation was most nonlinear near power facilities but became a nearly
linear function of emissions as plumes dispersed downwind.
1. Introduction
Power plants are the largest point source emitters of nitrogen oxides (NO
x
= NO
and NO
2
), yet emit very little volatile organic compounds (VOC). Ozone formation
in power plant plumes thus exhibits distinct features from that in other industrial
or urban plumes. Numerous modeling and observational studies have characterized
ozone formation in power plant plumes and its dependence on factors such as NO
x
emissions intensity and the extent of nearby VOC emissions (Luria et al., 2003;
Nunnermacker et al., 2000; Ryerson et al., 2001; Sillman, 2000; Springston et al.,
2005).
In this study, six power plants in Texas, three of which have the largest NOx
emissions in the state, are simulated with a high-order direct sensitivity method to
examine how the nonlinearity of ozone formation evolves as plumes disperse.
2. Methodology
The Comprehensive Air Quality Model with Extensions (CAMx) is applied with
the CB-05 chemical mechanism to simulate air quality during the period June
1-15, 2006. The modeling domain covers eastern Texas and surrounding states with
12-km resolution (
Fig. 1)
. Emissions and meteorology inputs were provided by the
Texas Commission on Environmental Quality (TCEQ, 2008). Model performance
was evaluated by comparison with ambient monitoring of ozone and other pollutants.
