decreasing particle size. The vast bulk of the
organic matter enriched in sea-spray aerosol is
water-insoluble organic matter. The chemical
composition of marine aerosol is shown in Fig. 3
for periods of low and high biological activity
over the North Atlantic as illustrated by oceanic
chlorophyll-a concentrations. Supermicron sizes
contain predominantly sea-salt, while for submicron sizes, the enrichment of water-insoluble
organic matter is linked to biological activity in
the ocean (the water-soluble organic matter in the
figure is also thought to be marine biogenic in
origin but formed from secondary processes).
In terms of anthropogenic sources of primary
aerosol, incomplete combustion (mainly from fossil fuel, but also from biomass burning and
cooking) results in pyrogenic aerosols in the
form of primary organic matter and soot (black)
carbon particles. Fossil fuel emissions result from
industrial, power plant, transport, and residential
heating sources and the resulting aerosol chemical
composition varies according to the fuel type and
the combustion technology used [14, 15]. Coal
combustion results in the emission of supermicron
fly-ash particles, while petroleum combustion
results in predominantly submicron carbonaceous
aerosols comprising soot carbon and organic
material [16]. In addition to primary emissions,
secondary aerosol precursors such as SO 2 , NO x ,
and hydrocarbons are also emitted from combustion sources.
Secondary Aerosol Formation via Nucleation
Homogeneous nucleation is the term used for the
spontaneous formation of an aerosol particle from
vapor phase precursors through a phase transition.
Homogeneous-homomolecular nucleation is the
self-nucleation of a single species, while
homogeneous-heteromolecular nucleation is the
self-nucleation of two or more species. Homogeneous nucleation occurs in a supersaturated vapor
phase where the saturation ratio (S) of a species in
air is the ratio of the species’ partial pressure to the
saturation vapor pressure in equilibrium with its
liquid phase at a given temperature. The Classical
Theory of nucleation is based on rate equations
relating to the random formation of vapor clusters
of more than one vapor molecule and the evaporation of these clusters [1]. The majority of these
clusters evaporate as quickly as they form since
Argentina
100 km
N
Atlantic
Ocean
Aerosol in Global Atmosphere, Fig. 2 Patagonian dust over the Atlantic Ocean. (Courtesy of NASA-MODIS)
244
Aerosol in Global Atmosphere
organic matter enriched in sea-spray aerosol is
water-insoluble organic matter. The chemical
composition of marine aerosol is shown in Fig. 3
for periods of low and high biological activity
over the North Atlantic as illustrated by oceanic
chlorophyll-a concentrations. Supermicron sizes
contain predominantly sea-salt, while for submicron sizes, the enrichment of water-insoluble
organic matter is linked to biological activity in
the ocean (the water-soluble organic matter in the
figure is also thought to be marine biogenic in
origin but formed from secondary processes).
In terms of anthropogenic sources of primary
aerosol, incomplete combustion (mainly from fossil fuel, but also from biomass burning and
cooking) results in pyrogenic aerosols in the
form of primary organic matter and soot (black)
carbon particles. Fossil fuel emissions result from
industrial, power plant, transport, and residential
heating sources and the resulting aerosol chemical
composition varies according to the fuel type and
the combustion technology used [14, 15]. Coal
combustion results in the emission of supermicron
fly-ash particles, while petroleum combustion
results in predominantly submicron carbonaceous
aerosols comprising soot carbon and organic
material [16]. In addition to primary emissions,
secondary aerosol precursors such as SO 2 , NO x ,
and hydrocarbons are also emitted from combustion sources.
Secondary Aerosol Formation via Nucleation
Homogeneous nucleation is the term used for the
spontaneous formation of an aerosol particle from
vapor phase precursors through a phase transition.
Homogeneous-homomolecular nucleation is the
self-nucleation of a single species, while
homogeneous-heteromolecular nucleation is the
self-nucleation of two or more species. Homogeneous nucleation occurs in a supersaturated vapor
phase where the saturation ratio (S) of a species in
air is the ratio of the species’ partial pressure to the
saturation vapor pressure in equilibrium with its
liquid phase at a given temperature. The Classical
Theory of nucleation is based on rate equations
relating to the random formation of vapor clusters
of more than one vapor molecule and the evaporation of these clusters [1]. The majority of these
clusters evaporate as quickly as they form since
Argentina
100 km
N
Atlantic
Ocean
Aerosol in Global Atmosphere, Fig. 2 Patagonian dust over the Atlantic Ocean. (Courtesy of NASA-MODIS)
244
Aerosol in Global Atmosphere