1. INTRODUCTION

Air quality problems have serious implications to public

health. In the United States, the Clean Air Act Amendments

of 1990 (CAAA-90) provide a societal mandate to assess

and manage air pollution levels to protect human health and

the environment. National and regional policies are needed

for reducing and managing the amount and type of

emissions that cause acid, nutrient, and toxic pollutant

deposition to ecosystems at risk and for enhancing the visual

quality of the environment. Human exposure to air

pollutants is one of the factors determining air pollution

standards. The U.S. Environmental Protection Agency

(EPA) established National Ambient Air Quality Standards

(NAAQS) that require development of effective emissions

control strategies for such pollutants as ozone and

particulate matter (PM). Eulerian air quality models

(AQMs) are used both to develop optimal emission control

strategies that are both environmentally protective and cost

effective and to advance atmospheric science understanding.

Because of the increased reliance on AQMs for the

assessment of air quality impacts on human and

environmental health, rapid improvements in the

parameterizations of atmospheric processes such as near

surface (i.e., planetary boundary layer), clouds, radiation,

aerosols, and linkage to global climate processes, as well as

application to regional and local air quality forecasting are

needed.

 

To meet both the challenges posed by the CAAA-90 and the

need to address the complex relationships among pollutants,

the U.S. EPA developed the Models-3 Community

Multiscale Air Quality (CMAQ) system (Novak et al. [1]).

Traditionally, AQMs have addressed individual pollutant

issues such as urban ozone, regional acid deposition,

particles, nitrogen, and toxics problems separately.

However, many of the air pollutants are subjected to the

same meteorology and oxidation processes. Therefore, one

of the main objectives of the CMAQ system is to apply a

“one atmosphere” multiscale and multi-pollutant modeling

approach based mainly on the “first principles” description

of the atmosphere while providing means to independently

but consistently model different pollutants, if necessary,

using the same tools. Needs for such third-generation

comprehensive air quality modeling systems were described

in Dennis et al. [2] and Byun et al. [3].

 

 

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