applied to SOA production from a-pinene ozonedriven oxidation and was found to predict firstgeneration products with 1 < C* < 10
7
mg m
$3
and 0.1 < O:C < 0.4. Given that generally
organics with C* < 10 mm
À3 will partition into
the aerosol phase, it is evident that most of the
oxidation products remain as volatile gases. The
first-generation products can then functionalize
through OH reactions resulting in a tripling of
SOA mass production after second-generation
oxidation. The model is able to predict the evolution of SOA in the 2D volatility and O:C space,
remaining consistent with the production key
products such as the first-generation cis-pinonic
acid, regarded as a semivolatile OOA, and
second-generation products such as a,a-dimethyltricarballylic acid, a low-volatility
OOA. Similar evolution was found for other
SOA sources like evaporated diesel and biomass
burning. This 2D volatility and O:C conceptual
has made considerable advances in simplifying
the treatment of an incredibly complex system
and can be further developed and extended to
include other key processes such as oligomerization. The combined perspective to emerge from
the recent mass spectral measurements and the
modeling framework is that most OA appears to
be an intermediate or transition state between
primary emissions and highly oxidized volatile
gases such as CO and CO 2 .
Global Aerosol Budgets, Burdens, and
Spatial Distributions
The diverse nature of aerosol sources from natural
and anthropogenic emissions, different formation
and removal processes, and different transport
mechanisms results in great inhomogeneity in
annual emission budgets, atmospheric burdens,
and spatial distributions of individual aerosol species. The result is ultimately significant variability
in radiative forcing and air pollution on regional
scales. To quantify budgets and distributions, general circulation (climate) models or chemical
transport models, are used in conjunction with
emission inventories. These models contain aerosol–cloud chemistry formation and evolution
modules along with deposition schemes and are
underpinned by field and laboratory studies into
key processes. In addition, quantification is
achieved by long-term observations of atmospheric composition at various point locations
around the globe. Remote sensing of aerosol
parameters from surface and space-borne platforms also provide added information on horizontal and vertical distributions.
Global Budgets
Atmospheric aerosols are derived from both natural and anthropogenic sources. Natural sources
include sulfate and sea spray (sea-salt and primary
organic matter) from the oceans, dust from desert
regions, particulate organic matter from biogenic
sources (both terrestrial and oceanic), and sulfate
and silicates from volcanoes. Anthropogenic
sources include sulfate, black carbon and primary
and secondary organic matter from fossil fuel
combustion and biomass burning, dust from
industrial sources, and nitrates mainly from transport emissions. The best estimated emissions and
resulting atmospheric mass and number burdens
are displayed in Table 1 [42]. The largest natural
emission is that of sea-salt with a “best guess” of
10,130 Tg a
À1 , followed by dust with a best guess
emission of 1,600 Tg a
À1 . Biogenic secondary
organic emissions are 25 Tg a
À1 , compared to
3.5 Tg a
À1 for anthropogenic emissions. For sulfate aerosol, anthropogenic emissions (122 Tg
a
À1 ) dominate over natural biogenic (57 Tg a
À1 )
and volcanic (21 Tg a
À1 ) emissions and for primary organic aerosol, anthropogenic emissions
amount to 95 Tg a
À1 while natural oceanic primary organic aerosol (not shown in Table 1) is
estimated to be 16 Tg a
À1 [56]. Black carbon
emissions from fossil fuel amount to 4.5 Tg a
À1 .
Global Burdens
The spatial distribution of total aerosol mass is
shown in Fig. 7. The distribution is a medium
mass composite from 10 global atmospheric climate (general circulation) models and chemical
transport models for the year 2000. From the
model output, the global average column burden
for all aerosol types is ~50 mg m
À2 , with regional
loadings exceeding 500 mg m
À2 , in places such as
252
Aerosol in Global Atmosphere
7
mg m
$3
and 0.1 < O:C < 0.4. Given that generally
organics with C* < 10 mm
À3 will partition into
the aerosol phase, it is evident that most of the
oxidation products remain as volatile gases. The
first-generation products can then functionalize
through OH reactions resulting in a tripling of
SOA mass production after second-generation
oxidation. The model is able to predict the evolution of SOA in the 2D volatility and O:C space,
remaining consistent with the production key
products such as the first-generation cis-pinonic
acid, regarded as a semivolatile OOA, and
second-generation products such as a,a-dimethyltricarballylic acid, a low-volatility
OOA. Similar evolution was found for other
SOA sources like evaporated diesel and biomass
burning. This 2D volatility and O:C conceptual
has made considerable advances in simplifying
the treatment of an incredibly complex system
and can be further developed and extended to
include other key processes such as oligomerization. The combined perspective to emerge from
the recent mass spectral measurements and the
modeling framework is that most OA appears to
be an intermediate or transition state between
primary emissions and highly oxidized volatile
gases such as CO and CO 2 .
Global Aerosol Budgets, Burdens, and
Spatial Distributions
The diverse nature of aerosol sources from natural
and anthropogenic emissions, different formation
and removal processes, and different transport
mechanisms results in great inhomogeneity in
annual emission budgets, atmospheric burdens,
and spatial distributions of individual aerosol species. The result is ultimately significant variability
in radiative forcing and air pollution on regional
scales. To quantify budgets and distributions, general circulation (climate) models or chemical
transport models, are used in conjunction with
emission inventories. These models contain aerosol–cloud chemistry formation and evolution
modules along with deposition schemes and are
underpinned by field and laboratory studies into
key processes. In addition, quantification is
achieved by long-term observations of atmospheric composition at various point locations
around the globe. Remote sensing of aerosol
parameters from surface and space-borne platforms also provide added information on horizontal and vertical distributions.
Global Budgets
Atmospheric aerosols are derived from both natural and anthropogenic sources. Natural sources
include sulfate and sea spray (sea-salt and primary
organic matter) from the oceans, dust from desert
regions, particulate organic matter from biogenic
sources (both terrestrial and oceanic), and sulfate
and silicates from volcanoes. Anthropogenic
sources include sulfate, black carbon and primary
and secondary organic matter from fossil fuel
combustion and biomass burning, dust from
industrial sources, and nitrates mainly from transport emissions. The best estimated emissions and
resulting atmospheric mass and number burdens
are displayed in Table 1 [42]. The largest natural
emission is that of sea-salt with a “best guess” of
10,130 Tg a
À1 , followed by dust with a best guess
emission of 1,600 Tg a
À1 . Biogenic secondary
organic emissions are 25 Tg a
À1 , compared to
3.5 Tg a
À1 for anthropogenic emissions. For sulfate aerosol, anthropogenic emissions (122 Tg
a
À1 ) dominate over natural biogenic (57 Tg a
À1 )
and volcanic (21 Tg a
À1 ) emissions and for primary organic aerosol, anthropogenic emissions
amount to 95 Tg a
À1 while natural oceanic primary organic aerosol (not shown in Table 1) is
estimated to be 16 Tg a
À1 [56]. Black carbon
emissions from fossil fuel amount to 4.5 Tg a
À1 .
Global Burdens
The spatial distribution of total aerosol mass is
shown in Fig. 7. The distribution is a medium
mass composite from 10 global atmospheric climate (general circulation) models and chemical
transport models for the year 2000. From the
model output, the global average column burden
for all aerosol types is ~50 mg m
À2 , with regional
loadings exceeding 500 mg m
À2 , in places such as
252
Aerosol in Global Atmosphere