NAI Concentration (number/cm3)

Level

Relationship With Health

≤500

1

Unfavorable

500 - 800

2

Normal

800 - 1100

3

Somewhat Favorable

1100 - 1400

4

Favorable

1400 - 1700

5

Quite Advantageous

1700 - 2000

6

Very Advantageous

≥2000

7

Extremely Advantageous