OVERVIEW

Aerosols are small particles suspended in the atmosphere. They have natural sources such as desert dust, sea salt, volcanic eruptions, and smoke from forest fires. They are also produced from the burning of coal, oil, and other fossil fuels; manufacturing chemicals; and driving cars and trucks.

When aerosol concentrations become high enough, they can pose serious health risks, especially to individuals with asthma and other respiratory problems. Airborne aerosols can also transport fungal and viral microbial pathogens, which can lead to disease outbreaks in other parts of the world.

Image above: In 2006, CALIPSO was launched into orbit around the Earth as part of the "A-train," a constellation of Earth observing satellites. CALIPSO provides the next generation of climate observations, including an advanced study of clouds and aerosols, drastically improving our ability to predict climate change and to study the air we breathe.

Aerosols can affect weather and climate. They have complex properties. Depending upon their shapes, sizes and composition they can reflect sunlight back to space and cool the atmosphere, they can also absorb sunlight and warm the atmosphere. Aerosols can even change the lifetimes of clouds, how much rainfall can occur, and how they reflect sunlight. They further can enable chemical reactions to occur on their surfaces and influence the composition of the atmosphere.

Measurements from satellites and ground stations show that many aerosols remain in the environment for long periods and can be carried by the winds hundreds of miles from their origin. In other words, the air we breathe is strongly affected by other countries' stewardship of the atmosphere — and vice versa.

To better predict the ultimate fate of aerosols, to help devise strategies for limiting pollution and to improve forecasts of harmful air quality conditions, we need better information on aerosol sources and how they enter the atmosphere and interact with weather patterns.

A key piece of information that is not provided by currently operating observational satellites is the altitude of aerosol layers in the atmosphere. Aerosols confined to the lowest part of the atmosphere are likely to be removed quickly by rain. On the other hand, those that are transported to higher altitudes are much more likely to travel long distances and affect air quality in distant countries. CALIPSO provides this vital missing piece of information.

Obtaining better information on the height of clouds is also needed. At present, weather prediction and climate models have considerable difficulty predicting the coverage, water and ice content and altitude of clouds. Inaccuracies in these parameters can lead to large errors in estimates of precipitation and the strength of the circulation. Observations from CALIPSO provide valuable new information that will help to improve weather and climate forecasts.