298 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



than in 1954. If the frequency and the severity of above- allowable 

 concentration periods should increase in the future city, then it must 

 be carefully considered by the city planners. Indeed, in that case, the 

 pollution situation is one of the parameters that must be taken into 

 account when projecting the population gains into the future. 



The problem has some similarity to the well-known interrelation- 

 ship between rabbits and grass. If a large amount of grass is avail- 

 able, the rabbits, having sufficient food, reproduce rapidly. But, with 

 their increased number, they consume more and more grass and finally 

 lack food. This in turn results in a lower reproduction rate and a 

 drop in the number of rabbits. Following that more grass grows, more 

 rabbits appear. As a result of this process, both the amount of grass 

 and the number of rabbits may fluctuate over several years. In atmos- 

 pheric pollution, it is quite possible to have a similar problem, although 

 it will be affected by more than two factors. 



Let us, for instance, consider the development of an urban area sur- 

 rounded by rural areas and let us assume that the area has at present 

 enough pollution to cause concern. If for some reason this urban 

 area attracts new inhabitants and new industries, then this will result 

 in an increase in atmospheric pollution. Following this increase, the 

 area may become less attractive to new inhabitants and the rate of 

 growth expected by the city planners may drop. In addition, the 

 rural areas may become so contaminated that a larger quantity of crops 

 and livestock is destroyed. Much of the necessary food, the quantity 

 of which increases with the population, will then have to be brought 

 from greater distances. This may or may not result in an increased 

 transportation problem, which would be followed by added pollutants. 

 It will, in any case, increase the living costs, which again will affect 

 the attractiveness of the urban area to new inhabitants. On the other 

 hand, some discouraged farmers may decide to give up their farms 

 to an industrial or residential expansion that, together with the pos- 

 sible growth of surrounding cities, will increase the pollution of the 

 urban area. 



To these various effects, one must also add those that will have an 

 influence on the population that still remains in the expanding urban 

 area. The increased health hazard and the higher probability of lethal 

 concentrations of pollution may have disastrous consequences. Such 

 disasters may not necessarily result in a reduction of the population by 

 death, but they may cause some of the inhabitants to leave the urban 

 area. Although we have not included all the parameters that have an 

 influence on the population growth, it should be obvious that this 

 process is more complicated than the one concerning rabbits and the 

 grass. It may, however, be followed in a similar way by a fluctuation 

 of both the number of inhabitants and the level of contamination over 



