Processing and Ageing in the Atmosphere - Mineral Dust: A Key Player in the Earth System - page 81

Tabl e 4. 1 Median percentage Fe solubility values for aerosol samples contained in the Sholkovitz
et al. ( 2012 ) data set

Region

Method N. Atlantic S. Atlantic N. Pacific N. Indian All oceans

All TFe concentrations
All methods

2.6 (419) 3.2 (91) 4.2 (270) 3.6 (157) 3.1 (960)

MQ 5.0 (150) 7.0 (122) 6.6 (112) 6.0 (384)

Acetate 2.0 (198) 3.2 (91) 2.5 (296)

Formate 2.2 (66) 1.4 (58) 1.4 (26) 1.7 (150)

Seawater 3.2 (5) 3.6 (90) 0.3 (19) 2.3 (121)

1- < 10 ng TFe m 3
MQ

9.6 (34) 20 (5) 10.0 (39)

Acetate 15 (13) 10 (9) 10.0 (25)

Formate 4.6 (8) 6.1 (15) 6.1 (23)

Seawater 7.0 (7) 6.6 (12)

10- < 100 ng TFe m 3
MQ

5.8 (79) 8.1 (46) 24 (26) 8.6 (151)

Acetate 4.1 (64) 3.6 (69) 3.7 (137)

Formate 2.3 (13) 1.2 (31) 1.5 (44)

Seawater 3.5 (4) 5.0 (46) 4.6 (52)

100- < 1,000 ng TFe m 3
MQ 1.0 (32) 7.8 (44) 5.3 (77) 5.2 (153)

Acetate 1.7 (79) 2.3 (13) 1.8 (92)

Formate 1.7 (41) 1.1 (12) 1.5 (22) 1.5 (75)

Seawater 2.6 (1) 1.4 (17) 1.0 (11) 1.2 (29)

1,000- < 10,000 ng TFe m 3
MQ 5.0 (5) 0.9 (27) 1.7 (9) 1.2 (41)
Acetate 0.7 (42) 0.7 (42)
Formate 2.4 (4) 1.0 (4) 1.4 (8)
Seawater 0.6 (20) 0.2 (8) 0.3 (28)
Values are given for the whole data and for subsets of the data obtained using Fe dissolution into
ultrapure water (MQ), pH 4.7 ammonium acetate buffer (Acetate), pH 4.2 formate buffer (Formate)
and seawater (Seawater). The data is also further subdivided according to the total atmospheric Fe
concentration of the samples

Sholkovitz et al. 2009 , 2012 ) have linked high Fe solubility in samples collected
from the western North Atlantic region to anthropogenic Fe emissions, using V (and
Ni) as tracers for combustion-derived Fe. While this source is not strictly “dust”,
this does suggest that there is some anthropogenic influence on Fe solubility, and
this influence is most likely to be significant at low dust concentrations.
Similar hyperbolic solubility - concentration relationships have been identified
for other dust components (e.g. Al, P and Si in aerosol (Baker and Jickells 2006 ), Al
in rainfall (Prospero et al. 1987 )). In Fig. 4.5 , we show percentage solubility - total
element concentration relationships for Fe, Al, Mn, P and Si for samples collected
over the Atlantic Ocean. Symbols in Fig. 4.5 indicate source regions for the samples,
based on 5-day air mass back trajectories (see Baker et al. 2006 ). While these