EXCHANGE OF MATTER BETWEEN ATMOSPHERE AND SEA 415 



particles. The curves for the two oceanic regions of Hawaii and the 

 Caribbean agree very well, whereas the curve for the Florida coast 

 shows much less fallout. The total rate of fallout proportional 

 to the surface area below the curves amounts to about 6 X lO"*^ 

 ng cm~2-sec~^ From the total concentration of salt in the air, the 

 average weighted fall velocity for the particulate matter is com- 

 puted to be about 0.7 cmsec~K Considering that precipitation may 

 remove as much as fallout, based upon arguments presented by 

 Eriksson, the velocity of removal should equal about 1.5 cm-sec~^ 



Blanchard and Woodcock (1956) made a very thorough study of 

 the production of sea salt particles by bursting bubbles in breaking 

 waves, and from their data Eriksson (1959b) also computed the 

 rate of production in a breaking wave. These results also are pre- 

 sented in Fig. 1 by the dotted line on a 600 times smaller vertical 

 scale as they give the same surface area as the Caribbean curve 

 One interesting thing is that the maximum in the production curve 

 is situated at much smaller particles than the fallout, suggesting a 

 rather far-reaching coalescence process in the atmosphere that 

 shifts the spectrum of the generated particles to the right. This is, 

 in fact, in accordance with other observations, and suggests that 

 these sea salt particles have a strong scavenging effect on foreign 

 matter in the atmosphere. 



As the rate of production per unit surface is about 300 times as 

 large as the total rate of removal, one may infer that, provided 

 breaking waves are the dominant source, about 0.3% of the ocean 

 surface is always covered by foam patches from breaking waves. 

 Observ^ations by Munk (1946) on the frequency of foam patches 

 and their size under different wind conditions give a coverage of 0.1 

 to 5% at wind forces of four or greater. An average of 0.3% for 

 the whole surface area of the oceans is, therefore, not unreasonable. 



Recently it has become fashionable to use the expression "resi- 

 dence time" for the ratio of mass to flux, an expression which is 

 certainly of great didactic value. The average residence time for sea 

 salts in the atmosphere is between one and two days. One must 

 remember, however, that most of the flux is made up of particles 

 greater than 10~^ fig, whereas a great deal of mass is found in parti- 

 cles less than this size. If transported inland, the residence time 



