3. Sulfur Cycling in Coastal Upwelling Systems
R = S/F
where R = residence time (years)
S = stock (grams/cur')
F = flux (grams/year)
Therefore. the stock of DMS in the atmosphere is:
DMS = FO*R
47
(Eq.3.4)
(Eq. 3.5)
where DMS = atmospheric DMS (grams)
R = residence time (years)
Residence time of a moderately reactive gas is approximately 1 week
(Lovelock et aI., 1972). The amount of sulfur dioxide formed from
atmospheric DMS is expressed by the following equation (Ferek,
Chatfield, & Andreae, 1986):
(CH 3hS + OH = S02 (40% yield)
(Eq.3.6)
Therefore, the amount of S02 produced is expressed by the equation:
S02 = DMS*O.4
(Eq.3.7)
where S02 = atmospheric sulfur dioxide
The quantity of S02' expressed as a mass, is then expressed as the density
of atmospheric sulfur dioxide of DMS origins as:
DS = SOIVAT
(Eq.3.8)
where DS = density of atmospheric sulfur dioxide of DMS origins
SO = mass of sulfur dioxide of DMS origins
VAT = volume of the atmosphere (nr')
Average density of cloud condensation nuclei (CCN) is 0.3 * 10- 3 ;
therefore, assuming all S02 becomes CCN, then the number of CCN per
cubic meter is:
CCN = DS/P
(Eq .3.9)
where P is the average size of a CCN.
Real-world data are still lacking on many aspects of the sulfur cycle,
and the variables included here are therefore generally defined. A spatial
model is thus a useful way to indicate areas of high and low DMS
production and to show how the values relate to other variables such as
cloud cover. A small area of the eastern Pacific is used in this study to