Long Range Planning

Other long-range problems caused by atmospheric chemical reactions occur in addition to those of sulfur and nitrogen compounds. States and provinces must formulate strategies to achieve oxidant air quality standards. They must assess both the transport of oxidants from outside local areas and the estimated influx of precursors that create additional oxidants. Lamb and Novak (1984) give the principal features of a four-layer regional oxidant model (see Figure 5.4.2) designed to simulate photochemical processes over time scales of several days and space scales of 1000 km. Temporal resolution yields hourly concentrations from time steps of 30 min and spatial resolution of about 18 km. The model includes the following processes:

• Horizontal transport

• Photochemistry using thirty-five reactions of twenty-three species

• Nighttime chemistry

• Nighttime wind shear, thermal stratification, and turbulent episodes associated with nocturnal jet

• Cumulus cloud effects, including venting from the mixed layer and photochemical reactions caused by their shadows

• Mesoscale vertical motion induced by terrain and horizontal divergence

• Mesoscale eddy effects on trajectories and growth rates of urban plumes

• Terrain effects on flow and diffusion

• Subgrid-scale chemical processes due to subgrid-scale emissions

• Natural sources of hydrocarbons and nitrogen oxides

• Wet and dry removal processes

The model was initially applied to the northeastern quarter of the United States. A 1980 emissions inventory gathered data on nitrogen oxides, VOCs, carbon dioxide, sulfur oxides, and total suspended particulate matter. In the model, volatile organics are considered as four reactive classes: olefins, paraffins, aldehydes, and aromatics. Applying the model requires acquiring and preparing emission and meteorological information for an area and a

Daytime

Layer 0

Layer 0

Inversion or Cloud Layer

Mixed Layer

VMarine Layer

Surface Layer a

Layer Functions

1. Downward transport of stratospheric ozone

2. Upward transport by cumulus clouds

3. Liquid and gas phase photochemistry

4. Long-range transport by free atmosphere

1. Gas phase photochemistry

2. Turbulence and wind shear effects on transport and diffusion

3. Deposition on mountains

4. Lake and marine layers

1. Effect on reaction rate of subgrid-scale segregation of fresh and aged pollutants

2. Ground deposition

3. Spatial variation in mean concentrations due to line, point, and area sources

Nighttime

Layer 3

Layer 2

0 0

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