content_image/613220.jpg
## 2.2.1. National Ambient Air Quality Standards 

EPA has promulgated National Ambient Air Quality Standards ( NAAQS) 5 to safeguard public health and environmental welfare against the detrimental effects of outdoor air Primary NAAQS are health -based standards geared toward protecting sensitive or at -risk portions of the population such as asthmatics, children, and the elderly. Secondary NAAQS are welfare oriented and are designed to prevent decreased visibility and damage to vegetation, and physical structures. 

NAAQS have been established for s ix criteria air pollutants shown in Table 2-1 ( National Ambient Air Quality Standards ) and they include carbon monoxide ( CO), lead (Pb), nitrogen dioxide (NO$_{2)}$, ozone (O$_{3)}$, particulate matter (PM), and sulfur dioxide (SO$_{2)}$. EPA periodically reviews the NAAQS to determine if revisions or supplements are warranted. 

<img src='content_image/613220.jpg'>

