Abstract
Abstract. During the second Texas Air Quality Study 2006 (TexAQS II), a full range of pollutants was measured by aircraft in eastern Texas during successive transects of power plant plumes (PPPs). A regional photochemical model is applied to simulate the physical and chemical evolution of the plumes. The observations reveal that SO2 and NOy were rapidly removed from PPPs on a cloudy day but not on the cloud-free days, indicating efficient aqueous processing of these compounds in clouds. The model reasonably represents observed NOx oxidation and PAN formation in the plumes, but fails to capture the rapid loss of SO2 (0.37 h−1) and NOy (0.24 h−1) in some plumes on the cloudy day. Adjustments to the cloud liquid water content (QC) and the default metal concentrations in the cloud module could explain some of the SO2 loss. However, NOy in the model was insensitive to QC. These findings highlight cloud processing as a major challenge to atmospheric models. Model-based estimates of ozone production efficiency (OPE) in PPPs are 20–50 % lower than observation-based estimates for the cloudy day.
Highlights
Power plants are the leading point source emitters of SO2 and oxides of nitrogen (NOx = NO + NO2)
Good agreement has been found in comparing power plant emissions reported by Continuous Emission Monitoring Systems (CEMS) with airborne measurements of power plant plumes (PPPs) (Frost et al, 2006) and with satellite measurements of NO2 (Kim et al, 2006)
PPPs observed during TexAQS II originated from eastern Texas coal-fired power plants with a large range of reported NOx and SO2 emission rates (Table 1 and Fig. 1)
Summary
The emissions, transport, and chemical evolution of pollutants from power plants have been investigated by multiple observational and modeling methods (Ryerson et al, 1998; Neuman et al, 2004; Godowitch et al, 2008a; Frost et al, 2006; Kim et al, 2006; Sillman, 2000). Several previous field studies have investigated the chemical evolution and lifetime of NOx, ozone production efficiency, and the loss rate of reactive nitrogen in PPPs (Ryerson et al, 1998; Springston et al, 2005; Neuman et al, 2009). This study utilizes the rich data source to examine whether a 3-D photochemical model with a fine spatial resolution but without subgrid plume treatment can effectively simulate the chemical and physical evolution of PPPs as they disperse and transport downwind. We focus on the evolution of sulfur, reactive nitrogen, and O3 in the plumes
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