anthropogenic sources of SO 2 –SO 42 - will dominate. These contrasting situations
are illustrated in Figs 7.19 and 7.20.
In Fig. 7.19 atmospheric measurements of particulate MSA, SO 42 - (after
subtraction of the component coming from sea salt, the so-called non-sea-salt-
sulphate (nss-SO 42 - )) and NH 4 +made in air at Mawson in Antarctica are shown.
This site is very remote from human activities and typically receives air which
has blown over thousands of kilometres of the Southern Ocean before being
Global Change 267nss–SO(ng m 4–3)2–180
160
140
120
100
80
60
40
20
0MSA (ng m-^3
)
1987 1988 1989 1990 1991
400
350
300
250
200
150
100
50
0
1987 1988 1989 1990 1991
100
90
80
70
60
50
40
30
201987 1988 1989 1990 199110
0NH+ (ng m-^3
)4Fig. 7.19Time series (1987–1991) of weekly average concentrations of methane sulphonic
acid (MSA), non-sea-salt-sulphate (nss-SO 42 - ) and ammonium (NH 4 +) measured at Mawson,
Antartica. After Savoie et al.(1993), with kind permission of Kluwer Academic Publishers.