TES is being used to compile a database of the substances that play an important role in the troposphere's chemistry, its interaction with living things, and its exchange of gases with the stratosphere. The instrument maps the location of these substances in three dimensions - not only with regard to latitude and longitude, but also altitude. And it measures how conditions vary over time, at global, regional, and local scales. The ultimate objective is to create a model of Earth's lower atmosphere that will enable scientists to understand its current condition and its likely future.

The Ozone Layer

TES is also measuring stratospheric ozone, along with the chemicals in that part of the atmosphere which are associated with ozone's destruction, to help determine how the ozone layer is responding to our attempts to stop the artificially induced damage and allow it to heal. As part of this study, it will help us understand the process by which some of these gases cross the boundary between the stratosphere and the troposphere.

Since TES observes the infrared radiation that is emitted by all substances warmer than absolute zero (using the same principle as night-vision goggles), the instrument can see at night as well as during the day. Therefore, unlike other instruments that monitor the ozone layer, TES can observe the atmosphere at Earth's polar regions even during their long nights, when they are inaccessible to instruments that rely on sunlight.

Ozone in the troposphere

Of the six pollutants singled out by the Environmental Protection Agency, ozone has proved to be the most difficult to assess and control. Ozone chemistry is very complex, making it difficult to quantify its contributions to poor local air quality. Further complicating the matter, at least some - and possibly as much as half - of the ozone in the troposphere originates up in the stratosphere, where we don't want to discourage its production.

TES is engaged in a multi-year global survey of ozone and its precursors, the chemicals involved in its production. TES's ability to generate vertical profiles of the atmosphere, distinguishing what is happening at different heights, is essential because different chemical reactions take place at different altitudes.

Data from TES will help scientists to determine which ozone occurs naturally in the troposphere, and which is the product of human creations such as motor vehicles and industrial activity. It will also further understanding of long-term variations in the quantity, distribution, and mixing of many other tropospheric gases which, though they constitute a tiny portion of the atmosphere, have a large impact on climate and air quality.

Global Warming

It is widely accepted in the science community that increased amounts of certain greenhouse gases in the troposphere are promoting a general increase in its temperature, especially at high latitudes. Some evidence indicates that the mean global temperature has risen about half a Celsius degree - nearly one Fahrenheit degree - over the past century. While this may seem to be a small change, it has important implications. Unless the trend is abated, many scientists fear that temperatures will rise 1.4 to 5.8 Celsius degrees (2.5 to 10.4 Fahrenheit degrees) by the end of this century. That could cause enough melting of polar ice caps and mountain glaciers to raise ocean levels by as much as a meter (40 inches), flooding coastal areas.

Whether the observed temperature increase is evidence of global climate change is a topic of current research and considerable public debate. TES will contribute a critical element that has been missing from the debate - a long-term global inventory of the gases thought to be responsible.

TES is measuring tropospheric water vapor, methane, and ozone, all of which are believed to have an impact on climate change, as well as additional gases important to tropospheric chemistry, such as carbon monoxide.

Other Objectives

TES is conducting simultaneous measurements of water vapor, ozone, carbon monoxide, and total reactive nitrogen oxides (NOy) to help determine the global distribution of OH (the hydroxyl radical), which is an oxidant of central importance in tropospheric chemistry. The instrument is also measuring NOy and SO₂ (sulfur dioxide) as precursors to the strong acids H₂SO₄ (sulfuric acid) and HNO₃, (nitric acid) that are the main contributors to acid rain.

Measurements from TES are helping to determine local atmospheric temperature and humidity profiles, local surface temperatures, and local surface reflectance and emittance (that is, the amount of sunlight reflected, and the amount of heat emitted by Earth's surface).

TES volcano-emission observations are being used for studies about the chemical state of the magma and the degree to which volcanoes are responsible for aerosols in the atmosphere, and to develop the means to predict eruptions and otherwise mitigate volcanic hazards. TES is also available to study emissions from forest fires and other events that affect the atmosphere.

The atmospheric models that will be developed from the TES database will be used to investigate such topics as:

• Changes in the oxidizing power of the troposphere and the distribution of tropospheric ozone caused by urban and regional pollution sources, particularly carbon monoxide, nitrogen oxides, methane, and other hydrocarbons.
• Sources and sinks (destructive reactions) of chemical species important to the generation of tropospheric and stratospheric aerosols.
• Natural sources of trace gases such as methane from organic decay, nitrogen oxides from lightning, and sulfur compounds from volcanoes.