NASA - National Aeronautics and Space Administration

We've all heard the saying: "It's the little things that make a difference." This is especially true for controlling climate. Scientists have long known that cloud droplets form on tiny, microscopic airborne particles - or aerosols. These particles allow water vapor to condense on their surfaces. Without them, cloud droplets, mist, fog or rain could not form at all. Pollution caused by human activities produces very significant amounts of additional aerosols. These airborne particles can cause substantial changes in our weather and climate.

Image to right: This is a true color image of the United Arab Emirates taken from Aqua-MODIS on August 10, 2004. A dust plume surrounds peninsular UAE/Oman and the Straight of Hormuz. Click on image to enlarge. Credit: NASA

To gain better understanding of aerosols, dozens of scientists from NASA, the U.S. Navy, United Arab Emirates (UAE), and research organizations from around the world are meeting in the Arabian Desert during August and September 2004 to decipher the impact of aerosols on the region's weather and climate.

The United Arab Emirates Unified Aerosol Experiment (UAE2) will rely on satellites, computer models, aircraft, and ground stations to understand the unique "mixing bowl" of desert dust, smoke, and man-made emissions worsened by the region's extraordinary meteorological conditions. Temperatures inland in UAE often exceed 122°F (50°C). Humidity over the Persian Gulf is high while away from the coast it often falls below 10%. Frequent land-sea breeze circulation also mixes air from over land and sea.

While many aerosols occur naturally, originating from volcanoes, dust storms, forest and grassland fires, some are created through human activities, such as altering natural surface cover and burning of fossil fuels and biofuels (e.g., wood and dung burning).

Scientists know that aerosol particles from factories and power plants increase the number of droplets in clouds and make those droplets smaller. In doing so, the pollutants create more reflective clouds that may retain their water longer and produce less rain. These results offer proof that our industrial processes and need for energy are changing the global climate and local weather systems.

Image to left: This is a color-coded image of temperatures of land and ocean around the United Arab Emirates taken from Terra-MODIS on August 10, 2004. It shows water temperatures from 29°C in the Gulf of Oman to 35°C in the Arabian Gulf (84°F to 95°F) and land surface temperatures exceeding 55°C (131°F). Click on image to enlarge. Credit: NASA

Aerosols can also cause cooling of the surface below them, since most are bright particles that reflect sunlight back to space, reducing the amount of solar radiation that can be absorbed at the surface. The magnitude of this effect depends on the size and composition of the aerosols, and on the reflecting properties of the Earth’s surface.

But, the cooling effect of the pollution aerosols will be somewhat regionally dependent, near and downwind of industrial areas. Greenhouse gases are more evenly distributed around the globe than aerosols. As a result, greenhouse gas warming is expected to be more uniform globally than aerosol cooling. No one knows exactly what the outcome will be of atmospheric warming in some regions and cooling in others. Climate models are still being developed to provide reliable insight into the possible outcome.

While UAE2 will measure the properties of aerosols, where they move, and help clarify whether they add or remove warmth, the mission will also help improve our measurement of aerosols from NASA's Terra and Aqua satellites. Taken together, the ground-based, aircraft and satellite measurements will give scientists a more comprehensive data set, allowing researchers to improve computer models and understand more exactly how our climate responds to aerosols.

Image to right: This is a map of the study area for the UEA2 Mission. Click on image to enlarge. Credit: NASA

Satellite data will be compared to remote sensing measurements made on the ground by various instruments. The Naval Research Laboratory's Mobile Atmospheric Aerosol and Radiation Characterization Observatory (MAARCO), NASA's Surface-sensing Measurements for Atmospheric Radiative Transfer (SMART), and 15 Aerosol Robotic Network (AERONET) instruments will gather data about mineral dust and pollutant aerosols over land and water. UAE2 is one of many research programs involving AERONET - a ground-based aerosol monitoring network and data archive supported by NASA. AERONET provides globally distributed near real time observations of several aerosol properties.

For more information, check out these related websites:

UAE2 Mission

UAE Department of Water Resources Studies (DWRS)

Aerosol Robotic Network (AERONET)

Scripps Institution of Oceanography

Mike Bettwy/Rob Gutro
Goddard Space Flight Center