Is the OTAG domain a well-defined air

quality control region?

The geographic domain of OTAG is indeed a well-defined air quality control region. The high ozone concentrations in excess of the tropospheric background originate from within the OTAG region, and the low ozone concentrations tend to originate outside the OTAG region. This means that the high ozone concentrations are not due to external influences but contributed by sources internal to OTAG. Furthermore, the high ozone concentration regions roughly coincide with the pattern of anthropogenic precursor emissions as modified by atmospheric dispersion. Consequently, it can be inferred that most of the excess ozone concentrations observed within the domain result from anthropogenic emissions.

Figure 1. a) Back trajectories for 22 receptor sites for low ozone days. These back trajectories point to outside the OTAG region as the source of low ozone. b)Back trajectories for 22 receptor sites for high ozone days (upper 50th percentiles). These back trajectories point to the OTAG region as the source of high ozone.