Page 82 - Fundamentals of Air Pollution

V. Air Quality Levels 55

C Adverse Responses to Air Quality Levels
The objective of air pollution control is to prevent adverse responses
by all receptor categories exposed to the atmosphere—human, animal,
vegetable, and material. These adverse responses have characteristic re-
sponse times—short-term (i.e., seconds or minutes), intermediate-term
(i.e., hours or days), and long-term (i.e., months or years) (Table 4-5). For
there to be no adverse responses, the pollutant concentration in the air
must be lower than the concentration level at which these responses occur.
Figure 4-9 illustrates the relationship between these concentration levels.
This figure displays response curves, which remain on the concentration
duration axes because they are characteristic of the receptors, not of the
actual air quality to which the receptors are exposed. The odor response
curve, e.g., to hydrogen sulfide, shows that a single inhalation requiring
approximately 1 sec can establish the presence of the odor but that, due
to odor fatigue, the ability to continue to recognize that odor can be lost
in a matter of minutes. Nasopharyngeal and eye irritation, e.g., by ozone,
is similarly subject to acclimatization due to tear and mucus production.
The three visibility lines correlate with the concentration of suspended
particulate matter in the air. Attack of metal, painted surfaces, or nylon
hose is shown by a line starting at 1 sec and terminating in a matter of
minutes (when the acidity of the droplet is neutralized by the material
attacked).

TABLE 4-5
Examples of Receptor Category Characteristic Response Times
Characteristic response times

Receptor Short-term Intermediate-term Long-term
category (seconds — minutes) (hours-days) (months-years)
Human Odor, visibility, Acute respiratory Chronic respiratory
nasopharyngeal disease disease, lung
and eye cancer
irritation
Animal, Field crop loss and Field crop loss and Fluorosis of
vegetation ornamental ornamental livestock,
plant damage plant damage decreased fruit
and forest yield
Material Acid droplet Rubber cracking, Corrosion, soiling,
pitting, nylon silver materials
hose destruction tarnishing, deterioration
paint
blackening