The Air Quality Analysis (AQA) workgroup of OTAG was specifically tasked to "identify, characterize, compare, and assess observational data and studies including but not limited to air quality trends analysis, overflight data, and meteorological studies for the purpose of evaluating the effects of the transport of ozone and its precursors on ozone nonattainment in the eastern United States." The primary benefit of the efforts of this workgroup is to "set the stage" for the useful interpretation of the modeling of future-year control strategies. The AQA efforts also provide a "climatological" view of the ozone problem, which extends beyond the modeled episode days and provides a broad perspective of the ozone problem and its characteristics. The major findings of this workgroup are listed below. For detailed discussion of these results, consult the AQA workgroup's 3-volume final report, available on the Internet.

The major findings of the Air Quality Analysis Workgroup are:

• Ozone transport does occur in the OTAG domain on local, sub-regional, and regional scales. Local transport, in the 30-150 mile range, likely contributes most to ozone nonattainment. Sub-regional transport occurs over the 100-300 mile range, and regional transport can occur over the 300-500 mile range, often including significant transport via nocturnal jets aloft. In general, the longer the transport distance, the lower the ozone impact.

• The perceived contribution of ozone transport is strongly dependent on how the ozone "problem" is defined. Local emissions are more important with respect to peak 1-hour concentrations than with respect to lower concentration thresholds and concentrations assessed over longer averaging times (8-hour or seasonal averages), where larger areas and longer distance scales become increasingly important.

• The central portion of the OTAG domain is truly unique with respect to ozone and ozone transport. It persistently has elevated ozone levels producing an "ozone pool." Transport in any direction from this region has been implicated with high ozone levels in neighboring areas.

• High ozone levels in the southern portion of the OTAG domain are typically associated with stagnant transport conditions resulting in shorter transport scales than on average. In contrast, high ozone levels in the northern portion of the OTAG domain are more typically associated with higher speed and persistent transport conditions from inside the OTAG domain.

• The proposed 8-hour ozone standard will result in significantly more nonattainment areas across the OTAG domain which will be closer together. This will make ozone transport more critical with respect to nonattainment than it is under the current standard.

• Visual comparison of ozone air quality data and model results shows that the simulations capture the large-scale features of each episode, suggesting that the model may be adequate as a tool for evaluating future regional control options. However, there appear to be tendencies for the model for the model to underpredict the highest ozone levels in the non-urban northern portion of the domain, overpredict the same for the southern portion of the domain, and underpredict the ozone aloft. One possible interpretation of these observations is that the model understates ozone transport, but the workgroup is not unanimous in this interpretation.

• Diagnostic comparisons of model results to ozone precursor data show significant discrepancies (especially for isoprene), suggesting that the model may be limited in its ability to assess control scenarios. This reinforces the notion that model results should be interpreted as one part of a full assessment, namely one which includes data analysis and modeling efforts.

• Peak ozone levels on weekends average much lower across the domain than those during the week, suggesting that control strategies which mimic weekday-to-weekend emission changes might effectively reduce peak ozone levels. Further investigation and quantification of associated emission changes are warranted.

• In most regions of the OTAG domain, peak ozone concentrations and the number of exceedances of the current (1-hour, 120 ppb) standard level have declined significantly over the last 15 years, indicating that currently implemented control strategies are directionally correct. While only a few major urban areas still exceeding the current standard several times per year, ozone nonattainment still exists across much of the domain. For the same time period, declines in the number of exceedances of the proposed (8-hour, 80 ppb) standard level are less pronounced.

• Transport of meteorological conditions does not occur on the same spatial scale as the transport of ozone, according to spatial correlation analyses; the characteristic spatial scale of temperature averages 700 miles whereas the spatial scale of ozone concentrations is closer to 350 miles. Nonetheless, the spatial scale of ozone transport derived from modeled OTAG episodes is typically less.

• The community of air quality analysts and the analytical networking capabilities that have been created as a result of OTAG have contributed substantially to the understanding of ozone pollution in general and ozone transport specifically. Nonetheless, much remains to be learned. Maintaining this network and its analytical capabilities is highly recommended.

• The OTAG process works -- even if not everyone agrees on every issue. Bringing together stakeholders, scientists, and policy-makers in such a forum has allowed for the development of high-quality analyses and encouraged the scientists to provide policy-relevant results. The entire OTAG community is considerably more informed than it was when the process began more than two years ago.