Chapter 2
The Chemical and Physical Properties of
Marine Aerosols: An Introduction
J. M. Prospero
2.1
Introduction
The atmosphere is an important pathway for the transport of particulate matter from
the continents to the oceans. Although the magnitude of these wind-borne fluxes is
not accurately known, there is evidence that some could be large enough to have a significant impact on chemical and biological processes in the oceans. In addition, windborne particles (i.e. aerosols) play an important role in climate-related processes which
in turn can have a great impact on physical, chemical, and biological processes taking
place in the oceans. Aerosols can affect climate directly by scattering and absorbing
both solar radiation and that which is re-emitted from the surface of the Earth to the
atmosphere. Aerosols playa critical role in water vapour nucleation processes. In this
way, they can affect the concentration and size distribution of cloud droplets, which
in turn can alter the radiate properties of clouds. The role of aerosols in cloud processes also affects the nature and distribution of rainfall and the subsequent distribution of clouds.
The role of aerosols in climate forcing has only recently received attention. Aerosols were largely ignored in the first Intergovernmental Panel on Climate Change
(IPCC) assessment. It was only in the 1995 IPCC report (IPCC 1996) that the importance of aerosols was acknowledged and an effort was made to estimate the forcing
due to anthropogenic particles. The report concluded that because of the many unknowns about the chemical, physical, and radiative properties of aerosols and their
temporal and spatial variability, only very crude estimates could be made. The IPCC
report and other studies have served to stimulate a broad research focus on aerosols
and climate-related processes, both in the laboratory and in the field. We have learned
much from these programmes, and it is now generally accepted that aerosols play an
important role in climate. We are now better able to constrain the estimates of forcing
or, at least, to better identify those parameters that must be better defined. Nonetheless, despite these advances, we still do not know enough about many aspects of aerosol properties and their role in climate to make a good assessment - indeed, our knowledge of aerosol processes is much worse than that of most greenhouse gases.
Another major change in the field is that we now have a better appreciation of the
types of aerosols that are important. For many years, the aerosol community has focused largely on sulphur (and related) chemistry because of concerns about the impact of sulphur pollution emissions on the atmospheric sulphur cycle. It was not until
the mid-90s that other aerosol species began to receive much attention. Today many
"natural" species are included in climate assessments: sea salt, mineral dust, and biogenic organics. The inclusion of these species is necessary for two reasons: so that we
The Chemical and Physical Properties of
Marine Aerosols: An Introduction
J. M. Prospero
2.1
Introduction
The atmosphere is an important pathway for the transport of particulate matter from
the continents to the oceans. Although the magnitude of these wind-borne fluxes is
not accurately known, there is evidence that some could be large enough to have a significant impact on chemical and biological processes in the oceans. In addition, windborne particles (i.e. aerosols) play an important role in climate-related processes which
in turn can have a great impact on physical, chemical, and biological processes taking
place in the oceans. Aerosols can affect climate directly by scattering and absorbing
both solar radiation and that which is re-emitted from the surface of the Earth to the
atmosphere. Aerosols playa critical role in water vapour nucleation processes. In this
way, they can affect the concentration and size distribution of cloud droplets, which
in turn can alter the radiate properties of clouds. The role of aerosols in cloud processes also affects the nature and distribution of rainfall and the subsequent distribution of clouds.
The role of aerosols in climate forcing has only recently received attention. Aerosols were largely ignored in the first Intergovernmental Panel on Climate Change
(IPCC) assessment. It was only in the 1995 IPCC report (IPCC 1996) that the importance of aerosols was acknowledged and an effort was made to estimate the forcing
due to anthropogenic particles. The report concluded that because of the many unknowns about the chemical, physical, and radiative properties of aerosols and their
temporal and spatial variability, only very crude estimates could be made. The IPCC
report and other studies have served to stimulate a broad research focus on aerosols
and climate-related processes, both in the laboratory and in the field. We have learned
much from these programmes, and it is now generally accepted that aerosols play an
important role in climate. We are now better able to constrain the estimates of forcing
or, at least, to better identify those parameters that must be better defined. Nonetheless, despite these advances, we still do not know enough about many aspects of aerosol properties and their role in climate to make a good assessment - indeed, our knowledge of aerosol processes is much worse than that of most greenhouse gases.
Another major change in the field is that we now have a better appreciation of the
types of aerosols that are important. For many years, the aerosol community has focused largely on sulphur (and related) chemistry because of concerns about the impact of sulphur pollution emissions on the atmospheric sulphur cycle. It was not until
the mid-90s that other aerosol species began to receive much attention. Today many
"natural" species are included in climate assessments: sea salt, mineral dust, and biogenic organics. The inclusion of these species is necessary for two reasons: so that we