Geoscience Reference
In-Depth Information
Table 2.2
Aerosol production estimates, less than 5
m radius (10
9
kg/year) and typical
concentrations near the surface (
μ
g m
-3
) in remote and urban areas
μ
Concentration
Production
Remote
Urban
Natural
Primary production:
Sea salt
2300
5-10
Mineral particles
900-1500
0.5-5*
Volcanic
20
Forest fires and biological debris
50
→
Secondary production (gas
particle):
Sulphates from H
2
S
70
1-2
Nitrates from NOx
22
Converted plant hydrocarbons
25
Total natural
3600
Anthropogenic
Primary production:
Mineral particles
0-600
Industrial dust
50
Combustion (black carbon)
10
100-500†
(organic carbon)
50
→
Secondary production (gas
particle):
Sulphate from SO2
140
0.5-1.5
10-20
Nitrates from NOx
30
0.2
0.5
Biomass combustion (organics)
20
Total anthropogenic
290-890
Sources: Ramanthan et al. 2001; Schimel et al. 1996, Bridgman 1990.
Notes: *10-60
g m
-3
during dust episodes from the Sahara over the Atlantic.
†Total suspended particles. 10
9
kg = 1Tg.
μ
pogenically derived). Natural sources are several
times larger than anthropogenic sources on a
global scale, but the estimates are wide-ranging.
Mineral dust is particularly hard to estimate due
to the episodic nature of wind events and the
considerable spatial variability. For example, the
wind picks up some 1500Tg (10
12
g) of crustal
material annually, about one-half from the Sahara
and the Arabian Peninsula (see
Plate 2.1
)
. Most of
this is deposited downwind over the Atlantic.
There is similar transport from western China and
Mongolia eastward over the North Pacific Ocean.
Large size particles originate from mineral dust,
sea salt spray, fires and plant spores (
Figure 2.1A
);
these sink rapidly back to the surface or are
washed out (scavenged) by rain after a few days.
Fine particles from volcanic eruptions may
reside in the upper stratosphere for one to three
years.
Small (Aitken) particles form by the conden-
sation of gas-phase reaction products and from
organic molecules and polymers (natural and
synthetic fibers, plastics, rubber and vinyl). There
are 500-1000 Aitken particles per cm
3
in air
over Europe. Intermediate-sized (accumulation
mode) particles originate from natural sources
