Pollutants monitored (in µg per cubic meter air sampled):
(1) total suspended particles (TSP)
(2) sulfur dioxide
(3) nitrogen oxides
(4) carbon monoxide
(5) ozone
(6) lead
(7) cadmium
The thresholds for air pollutants can be determined (footnote to Table 4, page S271):
(1) average annual concentration
(2) average daily concentration
(3) average 8-hour concentration
(4) average half-hour concentration
|
Maximum Level of Pollutants
|
Class
|
Quality
|
|
all <= 50% of threshold
|
I
|
clean or almost clean
|
|
1 pollutant 51 - 100% of threshold
|
II
|
moderately polluted
|
|
1 pollutant > 100% of threshold
|
III
|
polluted
|
|
1 pollutant > 100% of threshold; at least one other substance 51-100% of threshhold
|
IV
|
strongly polluted
|
|
>= 2 pollutants > 100% of threshold
|
V
|
heavily polluted
|
where:
• In the original table, Class IV was described as 1 substance above threshold with others <= half the threshold value. This statement seems no different than Class III. Also, in Class V suddenly 2 or more pollutants are above threshold. The wording above seems to make more sense.
• Class 0 air quality might be no chemical pollutants and minimal suspended particles; this would be clean air.
• The terms for quality seem to be a bit confusing. I would have used II as mild, III as moderate, IV as severe, and V as extreme.
