Contributions of regional transport and local sources to ozone exceedances in Houston and Dallas: Comparison of results from a photochemical grid model to aircraft and surface measurements

Abstract

[1] During the 2000 Texas Air Quality Study (TexAQS) and 2006 Texas Air Quality Study (TexAQS II) field experiments, aircraft measured ozone concentrations upwind, across, and downwind of the Houston and Dallas urban areas. Background ozone transported into Houston contributed, on average, approximately 50% and 66% of the total ozone on 8-h ozone exceedance days investigated by aircraft flights during TexAQS and TexAQS II, respectively. Analysis of a flight over Dallas on one exceedance day showed that transported ozone constituted 72% of the total ozone concentration. The aircraft measurements show that these two major metropolitan areas can be brought close to exceeding the 1997 8-h National Ambient Air Quality Standard for ozone of 0.08 ppm solely by the ozone contribution of regional transport before additional contribution from local sources. Large local contributions were also observed, particularly in Houston. Transport contributions to Dallas area ozone were quantified using the Comprehensive Air Quality Model with Extensions (CAMx) photochemical grid model and source apportionment methods. Model-predicted ozone concentrations were compared to ozone measurements from the aircraft and the surface monitoring network, and showed agreement on the importance of regional transport and local ozone formation. These results emphasize the benefits of regional control strategies, and suggest that local controls alone may not be sufficient to ensure attainment of the 8-h ozone standard in Houston and Dallas.

Issues with Ozone Attainment Methodology for Houston, TX

“…This work shows that observed spatial patterns in O 3 are not being predicted in the model and future work will focus on this issue. Model performance analysis is needed through trajectory 29 and air mass 30 analyses, process analysis, [31][32][33][34][35] and source apportionment modeling experiments 36 to more robustly link emission events of known or plausible location to measured and modeled O 3 . Further study is also needed to understand how other processes (e.g., boundary layer transport phenomena) can influence NTOCs.…”

Measurement of Ozone Production Sensor

“…Likewise, areas located on the path of influential meteorological features such as low level jets or high pressure systems are directly affected by ozone advection (Taubman et al, 2008;Kemball-Cook et al, 2009). In these particular situations, high concentrations of ambient ozone would come from transport of ozone rather than local ozone production.…”

Rural Southeast Texas Air Quality Measurements during the 2006 Texas Air Quality Study

“…Although local (county) measures have helped reducing peak ozone values, such as through reductions in petrochemical industry emissions in the Houston ship channel, it is unclear whether they will reduce plume ozone production and plume ozone mixing ratios in downwind, rural communities. 23 Current regional ozone modeling efforts 21,33,54 show that there are still inconsistencies that point to inadequate model input data, particularly precursor emission amounts and sources. If current emissions are insufficiently characterized, policy makers have limited information to make the necessary choices for SIPs that are intended to demonstrate future ozone NAAQS attainment.…”

“…A coastal city such as Houston is therefore expected to have slightly lower background levels than a site further inland. Nevertheless, ozone background dynamics at the College Station site, similar to Houston, 33 are expected to be driven largely by meteorological conditions. To illustrate this, we show in Figure 7a a period from July 2006 including three frontal passages.…”