270 



ANNUAL REPORT SMITHSONIAN INSTITUTION, 1956 



munity. After a certain time, they spread out into the rural areas, 

 reaching other communities, another State, or even another country. 

 The nature of some pollutants may change by chemical or physical 

 processes that take place during their dispersion. These processes 

 may be due to meteorological causes such as snow, rain, and fog or to 

 solar radiation and interactions with aerosols of natural origin, in- 

 cluding salt nuclei, volcano dust, pollen, or such gases as ozone and 

 nitrogen oxides. Various pollutants may interact among themselves, 

 DEATH RATES IN LONDON COUNTY 



7//////////////ZL 



x>& 



s*u- 





E3 Week No. I 



E3 Wee!< No. 2 

 rfweek No. 3 

 HI Week No. 4 

 E3 Week No. 5 

 Smog Period 



1000 2000 3000 4000 5000 



NUMBER OF DEATHS REGISTERED 



Figure 1. — Death rates in London County. Weekly death rates during several winter- 

 season smog periods are compared with the weekly rates preceding and following the 

 week of the smog period. 



disintegrate, or otherwise change during their dispersion. Except for 

 those pollutants that change into normal constituents of the atmos- 

 phere, the dispersing aerosols and gases come, after a certain time, 

 into contact with the surface of the earth. Most of the solid particu- 

 lates reach the land or the sea as a fallout ; other pollutants may be 

 washed down by the rain or may simply hit the ground when they are 

 spreading in the atmosphere. 



Atmospheric pollution starts with the production of pollutants — 

 often as undesirable or incidental consequences of various industrial 

 processes. An airborne cycle (fig. 5) for the pollutants begins with 

 the emission of pollutants; emission is followed by transfer through 



