5.2 Sources and Production Mechanisms of Atmospheric Aerosols
5.2.1 Introduction
The concept of a “source strength” is much more difficult to define
for aerosols than for most greenhouse gases. First, many aerosol species (e.g.,
sulphates, secondary organics) are not directly emitted, but are formed in the
atmosphere from gaseous precursors. Second, some aerosol types (e.g., dust,
sea salt) consist of particles whose physical properties, such as size and refractive
index, have wide ranges. Since the atmospheric lifetimes and radiative effect
of particles strongly depend on these properties, it makes little sense to provide
a single value for the source strength of such aerosols. Third, aerosol species
often combine to form mixed particles with optical properties and atmospheric
lifetimes different from those of their components. Finally, clouds affect aerosols
in a very complex way by scavenging aerosols, by adding mass through liquid
phase chemistry, and through the formation of new aerosol particles in and near
clouds. With regard to aerosol sources, we can report substantial progress over
the previous IPCC assessment:
- There are now better inventories of aerosol precursor emissions for many
species (e.g., dimethylsulphide (DMS) and SO2), including estimates
of source fields for future scenarios. The present-day estimates on which
this report is based are summarised in Table 5.2, see
also Figure 5.2.
- Emphasis is now on spatiotemporally resolved source and distribution fields.
- There is now a better understanding of the conversion mechanisms that transform
precursors into aerosol particles.
- There is substantial progress towards the explicit representation of number/size
and mass/size distributions and the specification of optical and hydration
properties in models.
| Table 5.2: Annual source strength for present day
emissions of aerosol precursors (Tg N, S or C /year). The reference year
is indicated in parentheses behind individual sources, where applicable. |
 |
| |
Northern
Hemisphere
|
Southern
Hemisphere
|
Globala
|
Range
|
Source
|
|
| NOx (as TgN/yr) |
32
|
9
|
41
|
|
(see also Chapter 4). |
| Fossil fuel (1985) |
20
|
1.1
|
21
|
|
Benkovitz et al. (1996) |
| Aircraft (1992) |
0.54
|
0.04
|
0.58
|
0.4-0.9
|
Penner et al. (1999b); Daggett et al. (1999) |
| Biomass burning (ca. 1990) |
3.3
|
3.1
|
6.4
|
2-12
|
Liousse et al. (1996); Atherton (1996) |
| Soils (ca. 1990) |
3.5
|
2.0
|
5.5
|
3-12
|
Yienger and Levy (1995) |
| Agricultural soils |
|
|
2.2
|
0-4
|
Yienger and Levy (1995) |
| Natural soils |
|
|
3.2
|
3-8
|
Yienger and Levy (1995) |
| Lightning |
4.4
|
2.6
|
7.0
|
2-12
|
Price et al. (1997); Lawrence et al. (1995) |
| NH3 (as TgN/yr) |
41
|
13
|
54
|
40-70
|
Bouwman et al. (1997) |
| Domestic animals (1990) |
18
|
4.1
|
21.6
|
10-30
|
Bouwman et al. (1997) |
| Agriculture (1990) |
12
|
1.1
|
12.6
|
6-18
|
Bouwman et al. (1997) |
| Human (1990) |
2.3
|
0.3
|
2.6
|
1.3-3.9
|
Bouwman et al. (1997) |
| Biomass burning (1990) |
3.5
|
2.2
|
5.7
|
3-8
|
Bouwman et al. (1997) |
| Fossil fuel and industry (1990) |
0.29
|
0.01
|
0.3
|
0.1-0.5
|
Bouwman et al. (1997) |
| Natural soils (1990) |
1.4
|
1.1
|
2.4
|
1-10
|
Bouwman et al. (1997) |
| Wild animals (1990) |
0.10
|
0.02
|
0.1
|
0-1
|
Bouwman et al. (1997) |
| Oceans |
3.6
|
4.5
|
8.2
|
3-16
|
Bouwman et al. (1997) |
| SO2 (as TgS/yr) |
76
|
12
|
88
|
67-130
|
|
| Fossil fuel and industry (1985) |
68
|
8
|
76
|
60-100
|
Benkovitz et al. (1996) |
| Aircraft (1992) |
0.06
|
0.004
|
0.06
|
0.03-1.0
|
Penner et al. (1998a); Penner et al. (1999b);
Fahey et al. (1999) |
| Biomass burning (ca. 1990) |
1.2
|
1.0
|
2.2
|
1-6
|
Spiro et al. (1992) |
| Volcanoes |
6.3
|
3.0
|
9.3
|
6-20
|
Andres and Kasgnoc (1998) (incl. H2S) |
| DMS or H2S (as TgS/yr) |
11.6
|
13.4
|
25.0
|
12-42
|
|
| Oceans |
11
|
13
|
24
|
13-36
|
Kettle and Andreae (2000) |
| Land biota and soils |
0.6
|
0.4
|
1.0
|
0.4-5.6
|
Bates et al. (1992); Andreae and Jaeschke (1992) |
| Volatile organic emissions (as TgC/yr) |
171
|
65
|
236
|
100-560
|
|
| Anthropogenic (1985) |
104
|
5
|
109
|
60-160
|
Piccot et al. (1992) |
| Terpenes (1990) |
67
|
60
|
127
|
40-400
|
Guenther et al. (1995) |
|
