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Control The Effect of Transport on Air Quality

Air Quality Conformity: Aims to ensure that transportation planning is consistent with clean air objectives for one or more of the following pollutants: ozone, carbon monoxide, particulate matter, and nitrogen dioxide.

Air Quality Models:  There are four generic classes of air quality modelling procedures: Gaussian; numerical; statistical or empirical; and physical. Gaussian models are most widely used for modelling non-reactive pollutants. Numerical models are most appropriate for urban applications involving reactive pollutants (such as ozone formation and dispersion), but require extensive input data and resources. Statistical or empirical models are “second-best” techniques that are frequently employed when incomplete scientific understanding or lack of data make the use of a Gaussian or numerical model impossible. Physical modelling is technically detailed and resource intensive, involving the use of wind tunnel or other fluid modelling facilities, but may be applicable for complex flow situations such as complex building or terrain conditions.

In addition to the various classes of models, there are two basic levels of model sophistication: screening models; and refined models. Screening models consist of relatively simple estimation techniques to identify sources, which will clearly not cause or contribute to ambient concentrations, which exceed the allowable increment, thus eliminating the need for more detailed modelling. Refined models provide more detailed treatment of physical and chemical atmospheric processes, require more detailed and precise input data, and provide more specific estimates.

Emission Reductions: Emissions reduction efforts range from producing lower-emitting new vehicles to reducing vehicle use.  Efforts to reduce emissions focused on producing vehicles, which emitted less pollution.  Despite the progress in reducing the emission rates from new vehicles, emission system component failure, lack of proper maintenance, tampering, and the normal deterioration of emission control system performance all act to offset these emission benefits.

Increased attention has been focused on control measures intended to reduce emissions from in-use vehicles. These reductions can come from technology improvements.  Technology improvements offer a number of innovative approaches to reducing emissions. In fact, I/M programmes (Vehicle Inspection & Maintenance) represent one of the first and perhaps most widespread of the technology-based control measures targeted at in-use vehicles.

Ambient Air Quality Standards: An ambient air quality standard sets legal limits on the level of an air pollutant in the outdoor (ambient) air necessary to protect public health.