Chapter 13 
The physics and chemistry of a burning cigarette are exceedingly 
complex. For example, filter ventilation involves two mechanisms. In the 
first, fresh air from the outside is admitted to the filter and mixes with the 
smoke. As a result of this ventilation, a smaller effective puff is drawn on 
the burning end of the cigarette and less tobacco is then consumed during 
the puff. In addition, the smoke velocity in the cigarette is dramatically 
reduced, and the filter efficiency upstream of the ventilation holes increases. 
Similarly, in the second, a higher paper porosity also allows more outside air 
to enter the smokestream, also reducing the effective puff volume at the fire 
cone. The various cigarette design parameters result in many interactive 
effects on the performance of the cigarette. 
The changes in cigarette design to reduce tar and nicotine yields have 
not been limited to low-tar and ultralow-tar products. Even today's 
nonfiltered cigarettes, the so-called high-tar brands, have about half the 
tar yield of their 1950's counterparts. 
As a result, consumers today have a much wider range of choices in tar 
and nicotine than they did previously, and all cigarettes are substantially 
lower in tar yields than they were in past years (Figure 2). Cigarette design 
changes have resulted in an overall major reduction in smoke yields. 
Figure 2 
R.J. Reynolds Tobacco Company offers smokers a range of tar levels (1955-1993, 
in 5-year intervals) 
1955 1960 1965 1970 1975 1980 1985 1990 1993 
Year 
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