Encyclopedia of Environmental Science and Engineering, Volume I and II

ATMOSPHERIC CHEMISTRY 119

One of the principal goals of air-pollution research is to

obtain and use our detailed knowledge of emissions, topogra-

phy, meteorology, and chemistry to develop a mathematical

model that is capable of predicting concentrations of primary

and secondary pollutants as a function of time at various loca-

tions throughout the modeling domain. These model results

would be validated by comparison with ambient-air-monitor-

ing data. Model refinement continues until there is acceptable

agreement between the observed and predicted concentra-

tions. This type of air-quality model, on an urban scale, is

called an airshed model. Airshed models treat the effects of

a set of stationary and mobile sources scattered throughout a

relatively small geographical area (
100 km^2 ). These models

are intended to calculate concentrations of pollutants within

this geographical area and immediately downwind.

It is also necessary to develop a detailed knowledge of the

impacts of pollutants on the various important receptors, such

as humans, plants, and materials. This impact information

is used to identify the pollutants that need to be controlled.

An airshed model can be used to predict the effectiveness

of various proposed control strategies. This information can

be passed on to legislative authorities, who can evaluate the

costs and benefits of the various strategies and legislate the

best control measures.

Unfortunately, there are significant gaps in our knowledge

at every step throughout this idealized air-pollution system.

Sources

Emissions of

Anthropogenic, Biogenic, Geogenic

Primary Pollutants e.g.

VOC, NOx, SO 2 , CO, PM10,2.5, HAPs

Dispersion

and

Transport

Chemical and Physical

Transformations

Scientific Risk Assessment

Effects:

Health and

Environmental

Exposure

Monitoring

FATES

Wet and Dry

Deposition

Transport to Stratosphere

Stratospheric Chemistry,

Ozone Depletion

Models

Local “Hot-Spot”

Plume, Airshed,

Long-range

Transport,

Global

Risk Management Decisions

Air Pollution Control

Impacts on Receptors

(Humans, Animals,

Agricultural Crops

Forest and Aquatic

Ecosystems, Visibility,

Materials, etc.)

Long-Lived Species

e.g. CFC, N 2 O

Ambient Air

Urban, Suburban,

Rural. Remote, O 3 ,

Acids, Toxics. PM10,2.5 etc.

FIGURE 1 The atmospheric air-pollution system. From Finlayson-Pitts and Pitts (2000). (HAPs—

hazardous air pollutants). With permission.

C001_008_r03.indd 119C001_008_r03.indd 119 11/18/2005 10:15:19 AM11/18/2005 10:15:19 AM