EXCHANGE OF MATTER BETWEEN ATMOSPHERE AND SEA 413 



the sea surface due to inertia forces can be of importance compared 

 with the rate of fallout by gravity. Over vegetation-covered land 

 areas impingement on leaves and other small obstacles seems to be 

 a rather important process for removing particulate matter from 

 an air stream. 



Summarizing, we can state that the flux of gaseous matter close 

 to the air-sea interface is given by 



^gas = -D"- (2) 



where D is the molecular diffusion coefficient. For an aggregate 

 constituent, we consequently have 



/^aggr. = Vp (3) 



in the same region. 



For a gas the transport in the turbulent region, is, of course, by 

 turbulent diffusion, but for particulate matter turbulent transport 

 will take place only if the fall velocity of the particles in the laminar 

 boundary layer is greater than in the turbulent region. It can be 

 shown that even hygroscopic sea salt particles are transported 

 downward almost entirely by gravity, as the moist laminar boundary 

 layer hardly affects the average fall velocity of these particles. 



In the case of simultaneous production of sea salt particles by 

 bursting bubbles, the downward flux of particles in a steady state 

 is balanced by an upward turbulent flux. 



Aggregate Exchange 



In viewing first aggregate exchange over ocean areas, the exchange 

 ot sea salts in particulate form is no doubt best known. It has been 

 suggested, however, that organic matter enriched in surface films is 

 also carried into the air by bursting bubbles. However likely this 

 process seems, no direct evidence concerning it exists. We shall 

 therefore limit our considerations on aggregate exchange to sea 

 salt particles. 



The rather extensive data furnished by Woodcock and his col- 

 laborators on the frequency distribution of sea salt particles in the 

 air o\^er oceans enables one to make certain estimates on the rate 



