Aerosol Particles

What is Aerosol Particle

Definition of Atmospheric Aerosol Particles

Aerosol particles are solid or liquid components suspending in the air. Their sizes vary from several nanometers to millimeters. The numbers are huge; one breathe contains several million particles, some of which are then inhaled into the body.

Aerosol particles occur in the atmosphere from the ground surface by wind, direct exhaust from factories and/or automobile, and splash of ocean waves. They are also formed due to secondary reactions of gases condensations in the atmosphere.

The lifetime of aerosol particles in the atmosphere depends on the altitude and the sizes. The bigger the particles are, the shorter lifetime they have. Aerosol particles deposit on the ground due to rain and/or gravity. Some particles (e.g. from volcano) can suspend in air for years. These particles affect the earth's atmosphere and climate.

The aerosol particles in the atmosphere will be transported for several hundreds to thousands km by the global scale wind and spread across the world. During the transportation process, the aerosol particles coagulate each other or are exposed to gases and water vapor, resulting in greatly changing their compositions and shape. When the shape and formation of an aerosol particle is changed, the effect it has on the climate also changes. Therefore, detailed observations are important to understand their processes.

Effects of aerosol particles on Environment and Weather

Aerosol particles absorb and scatter sunlight in the atmosphere, and they cause greenhouse and cooling effects in the global scale. Aerosol particles scatter sunlight and reduce visibility near the ground (Image 1). Moreover, the aerosol particles become cloud condensation nuclei and proceed the formation of cloud droplets.

Hazy day Clear day

Image1: Hazy day (left) and a clear day (right). The mountain becomes difficult to see because of the aerosol particle scattering. The photos were taken at the Nexus of Air Quality and Climate Change research project, CalNex's campaign in California Institution of Technology

The optical properties of aerosol particles vary depending on their composition, sizes, and concentrations. Therefore, different types of aerosol affects differently on the climate. The results could vary from greenhouse effect to cooling effect, indicating that analyzing individual particles is important to understand their impacts.

Electron microscope can be used to magnify aerosol particles and examine their internal compositions. Such studies will be applied to climate model, helping to understand how aerosol affects weather and climate in details. This could lead to resolving questions of whether its emission or reduction has any impact to the global climate. Such information is also important for emission regulation policies.

Electron microscope image

Image 2: Electron microscope image of aerosol sample from Australia. The black areas are the aerosol particles collected on the filter. Okada et al. (2005 Atmospheric Environment).