Dustfall Jars

The simplest of all air quality monitoring devices is the dustfall jar (see Figure 5.10.7). This device measures the fallout rate of coarse particulate matter, generally above about 10 ¡m in size. Dustfall and odor are two major reasons for citizen complaints concerning air pollution. Dustfall is offensive because it builds up on porches and automobiles and is highly visible and gritty to walk upon.

Dustfall seldom carries for distances greater than As mi because these large particles are subject to strong gravitational effects. For this reason, dustfall stations must be spaced more closely than other air pollution sensors for a detailed study of an area.

Dustfall measurements in large cities in the United States in the 1920s and 1930s commonly indicated dustfall rates in hundreds of tn per sq mi per mon. These levels are considered excessive today, as evidenced by the dustfall standards of 25 to 30 tn per sq mi per mon promulgated by many of the states. While the measurement of low or moderate values of dustfall does not indicate freedom from air pollution problems, measured dustfall values in excess of 50 to 100 tn per sq mi per mon are an indication of excessive air pollution.

The large size of the particulate matter found in dustfall jars makes it amenable to chemical or physical analysis by such techniques as microscopy. These analyses are useful to identify specific sources.

0 0

Post a comment