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The mission of CAICE is to transform our ability to accurately predict the impact of aerosols on climate and our environment by bringing real-world chemical complexity into the laboratory.

What is an aerosol?


Some sources of aerosol particles are natural (mineral dust, sea spray), while others are human-influenced (urban smog, vehicle exhaust).

An aerosol is a collection of small liquid or solid particles that are suspended in a gas.  Smoke, sea spray, smog, and desert dust are a few examples of aerosols that can be found in the air around us.  The Earth’s atmosphere contains thousands (or more!) aerosol particles in every liter of air, everywhere on our planet, but the exact type and number of particles is not the same in all locations around the world.  Aerosol particles can come from natural sources (sea spray, desert dust) or from human activity (car exhaust, fires, smog), meaning the local environment has a big effect on the types of particles in the air.  These small airborne particles can be important to air quality and human health, and at the same time, play a key role in Earth’s climate.

How do aerosol particles influence the Earth’s climate?


The Direct Aerosol Effect. Aerosol particles scatter radiation back to space, which has a cooling effect on the Earth’s energy balance.

Indirect Effect

Indirect Aerosol Effects. The number of aerosols that can act as cloud droplet seeds influences both the reflectivity of a cloud and its ability to produce precipitation.

Aerosol particles can scatter (reflect) or absorb sunlight, altering the amount of the sun’s energy that enters the Earth’s climate system– to climate scientists, this is called the “Direct Aerosol Effect.”  The chemical composition of aerosol particles determines how well they can grow in size by gathering liquid water through condensation, which influences their size and thus their ability to scatter light — on a per-particle basis, larger particles scatter more light than smaller aerosol particles.

In addition, aerosol particles act as the seeds for cloud droplets. In this way, aerosol particles can influence the albedo (“whiteness” or reflectivity) of a cloud in addition to affecting its ability to produce precipitation.  The nature of the cloud droplet seed can also influence the temperature at which liquid cloud droplets freeze, further influencing the ability of the cloud to precipitate.  Altogether, these are called “Indirect Aerosol Effects.”

Learn more about CAICE research efforts in Aerosol-Climate Interactions

What role does chemistry play?

Chemistry is the lynchpin in the impacts of aerosols on climate.  The composition and properties of the aerosol interfaces control chemical reactions which occur in the atmosphere and/or determine the ability of a particle to accommodate water (to grow in size or act as a cloud droplet seed).  CAICE is currently studying aerosol particles which are formed in oceanic regions — either by direct emission from the ocean (a.k.a. “sea spray aerosol”) or through chemical reactions in the atmosphere where particles are “nucleated” from clusters of molecules that were originally in the gas phase.

Aerosol particles from the ocean are rich with chemical complexity and constitute a major global source of aerosol particles to the atmosphere.  CAICE is studying these particles from both experimental and theoretical perspectives.


Experimental Approaches

A panorama of the fully instrumented air-sea interaction facility at the SIO Hydraulics Laboratory during the CAICE Intensive Campaign in 2011.

A fish-eye view of the linear wave channel facility at the SIO Hydraulics Lab.

CAICE researchers are using new innovative tools (like the Linear Wave Channel, shown at left) to generate sea spray aerosol in ways that mimic natural wave breaking in ways that are closer to the real ocean than ever before.  Populations of aerosol particles are analyzed individually using mass spectrometry and microscopy.  The information learned from these experiments help to steer more detailed experiments that can probe the fundamental chemical interactions at the molecular level, particularly at chemical interfaces.  In order to bring real-world chemical complexity into the laboratory, CAICE has also been using marine phytoplankton and bacteria as miniature ‘chemical factories’ for our experiments — this allows us to study a richly complex chemical system which is representative of the open ocean.

Theoretical Approaches

A chemical simulation of organic molecules on the surface of an aerosol particle. [Blue = water, green = sodium, organic molecules are magenta and white]

A chemical simulation of organic molecules on the surface of an aerosol particle. [blue = water, green = sodium, magenta and white = ocean-relevant organic molecules]

Theoretical chemistry helps us build detailed chemical models of aerosol particles so that we can gain the ability to predict the influence of aerosols on climate through fundamental chemistry.  For instance, the arrangement of molecules at the surface of sea spray aerosols influences the chemical reactivity of these particles in the lower atmosphere which can have an effect on air quality in coastal regions.  A high level of uncertainty exists in our fundamental understanding of these processes, limiting our ability to predict the impact of aerosol particles on climate.