Microscale and Regional Modeling and Emission Models
Air quality analysis for mobile sources, in most cases, is very complex and performed by combinations of computer models. There are basically three types of models required to perform air quality analysis.
The first type is the model describing and projecting vehicle activities of the facilities to be analyzed. In general, transportation professionals use two modeling scales, transportation planning models (interested in regional analysis) or traffic models (interested in local transportation facilities such as individual roadways, intersections, and ramps, etc.). The second type of analysis (emissions rate models) represents the process of estimating emissions by vehicle fleets. When emission rates are combined with vehicle activity data, the result is an estimate of emissions by time and space. One good example of this analysis is presented in the region wide emissions inventory procedures (Ref: Clean Air Act Amendments of 1990). Once the vehicle activities are estimated, and combined with the emissions rates, emissions output can be dispersed in the atmosphere (pollution dispersion model). This third type of analysis is performed to estimate pollution concentrations.
This final model is needed to estimate pollutant concentrations to which humans are exposed. In this analysis, temporal and spacial estimates of pollutants from transportation and other sources, along with estimates of background pollution and weather conditions, are combined. When this analysis is completed, comparisons of estimated pollution concentrations with the National Ambient Air Quality Standards (NAAQS) are made to determine whether control action is needed.
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