Special session of California 2000 field study - Air Pollution Modeling and Its Application - page 546

Moreover, evaluations focused on absolute concentration may not be ideal for
determining a model's ability to predict a relative change in pollutant concentration
corresponding to an emission change.
Fig. 2. Modeled and simulated daily average PM 2.5 nitrate concentration at FSF site
Ratios and indicators . Estimates of the relative change in pollutant concentration
associated with a change in emissions are used in developing plans for attaining
air quality standards. Therefore predictions of pollutant ratios and photochemical
indicators should be evaluated in addition to absolute concentration. In Fig. 3, the
ratio of PM 2.5 nitrate to total inorganic concentration is compared with observations.
Performance for the nitrate ratio differs from that for absolute nitrate concentration
(Fig. 2) . In Fig. 4, predictions of an indicator of photochemical regime are compared
with observations. For much of the simulation, the model correctly predicts ozone-
to-NO X ratios of less than 15.
Fig. 3. Modeled and simulated daily average PM 2.5 nitrate ratio at FSF site
Fig. 4. Modeled and simulated hourly ozone-to-NO X ratio at FSF site