Smoking and Tobacco Control Monograph No. 7 
and Human Services, 1988). Jarvis and Russell (1985) first observed for 
English cigarettes that the smoke delivery of nicotine was not reduced to 
the same extent as that of the tar. During the past 10 to 15 years, the same 
observation was made for U.S. cigarettes. Figure 1 does not reflect the 
gradual change in the tobacco blend of U.S. cigarettes with regard to an 
increase of the hurley tobacco share from about 35.9 percent in 1950 to 
46.5 percent in 1982; the remainder of the tobacco blend consists primarily 
of bright tobacco with about 5 to 8 percent oriental tobacco and 1 percent 
Maryland tobacco (Grise, 1984). 
CHANGES IN 
CIGARETTE 
DESIGN AND 
COMPOSITION 
Cigarettes With 
Filter Tips 
Since 1955 the U.S. sales-weighted average smoke yields have 
declined from 38 mg tar and 2.7 mg nicotine to 12 mg and 0.95 mg, 
respectively (Figure 1). A major reason for the decrease in smoke 
yields is the wide acceptance of filter cigarettes. Their use steadily 
increased in America from 0.56 percent of all cigarettes smoked in 
1950 to 19 percent in 1955, 51 percent in 1960, 82 percent in 1970, 
92 percent in 1980, and more than 97 percent since 1993 (Figure 2) 
(Hoffmann and Hoffmann, 1994b; U.S. Department of Agriculture, 1993). 
Most filter tips (15 to 35 mm) are made of cellulose acetate; only a low 
percentage of cigarettes are made with composite filters of cellulose acetate 
with charcoal. Since about 1968, increasing proportions of the cellulose 
acetate filter tips are perforated with one or more lines of tiny holes placed 
near the middle of the filter tow. Today up to 50 percent of all cigarette 
filter tips in the United States have various degrees of perforations. The 
conventional filter cigarettes are acceptable to consumers with a maximal 
draw resistance of up to about 130 mm water column (Kiefer and Touey, 
1967). The filters reduce primarily the smoke yields of particulate matter 
and thus the nonvolatile smoke constituents. The efficiency of cellulose 
acetate filters for total particulate matter (TPM) removal can be increased by 
reducing the diameter of the filaments without increasing the draw resistance 
(Table la) or by using a longer filter tip (Table lb). In the mainstream smoke 
of the U.S. blended cigarette with a pH below 6.3 to 6.5, more than 90 percent 
of the nicotine is present in the particulate matter as a salt with organic acids 
(Kiefer and Touey, 1967; Brunnemann and Hoffmann, 1974). 
Conventional cellulose acetate has the capability to selectively reduce 
some of the volatile and semivolatile compounds in the smokestream, 
especially when the filter is treated with certain plasticizers, such as glycerol 
triacetate. Some of the volatile smoke constituents that are ciliatoxic agents, 
such as acrolein, are removed selectively, even beyond the reduction of 
I'PM, by retention on such treated filter tips. Phenols and cresols, a group 
of semivolatiles, also are removed selectively up to 80 to 85 percent, as are 
the highly carcinogenic dialkylnitrosamines, of which up to 75 percent can 
be retained on cellulose acetate filters (George and Keith, 1967; Brunnemann 
and Hoffmann, 1977). 
Filter tips with perforations allow dilution of the smoke with air. 
Moreover, drawing puffs through perforated filter cigarettes reduces the 
velocity of the air drawn through the burning cone. As a result, less of the 
18 
