The need to study Earth's environment has intensified over the last half century. Increasing industrialization, deforestation, and use of fossil fuels throughout the world have had far-reaching effects on air quality, and appear to be contributing to global warming and changing weather patterns. Since winds can carry pollutants great distances, efforts to improve air quality require international cooperation and a global perspective. Viewing Earth's atmosphere from space can improve our understanding of the forces that shape it, and provide insights into how we can better care for it.

Given the huge scope of the problem, it may be surprising to learn that TES is designed to measure an assortment of gases that, all together, amount to about one-tenth of one percent of the Earth's atmosphere. Why all this attention on such a minor portion of the air? Because these "trace" gases have a disproportionate impact when it comes to air quality, climate, and protection from the sun.

Ozone

The U.S. Environmental Protection Agency has identified six "criteria pollutants" as indicators of air quality: ozone, carbon monoxide, nitrogen dioxide, sulfur dioxide, lead, and particulates (aka aerosols). TES is measuring all of these substances with the exception of lead.

Ozone is drawing particular attention. Ozone is a cousin of the oxygen molecule on which we depend for life. While the oxygen molecule consists of two oxygen atoms, the ozone molecule consists of three. That extra atom makes a big difference, in some ways that benefit us, and in other ways that are harmful.

About 90% of the ozone in our atmosphere resides in the stratosphere, where it protects humans and other living things by absorbing much of the ultraviolet (UV) portion of sunlight before it can reach us and cause skin cancer, cataracts, agricultural damage, and other problems. Until relatively recently, the amount of ozone in the stratosphere has been regulated by a natural process in which it is generated by the action of sunlight on oxygen molecules, and destroyed in reactions with other naturally occurring airborne gases.

But beginning in the 1970s, scientists discovered that the natural balance between production and removal was being disrupted by certain chemicals, especially the chlorofluorocarbons (CFCs) that were commonly used in refrigeration and as spray-can propellants. Photochemical reactions with these compounds have been accelerating the rate at which ozone is destroyed, causing a general thinning of the ozone layer worldwide and a seasonal hole over Antarctica.

International treaties have reduced the amount of ozone-damaging chemicals being introduced into the atmosphere. TES is helping to determine whether the ozone layer is recovering as a result.

Troposphere

While ozone is an asset in the stratosphere, however, it has a mixed impact when it resides lower down, in the troposphere - the bottom layer of the atmosphere, which extends from the ground to where the stratosphere begins, at an altitude of about 16 km (10 miles). This, of course, is where we live. It is also where most weather takes place.

On the positive side, ozone reacts with water vapor and sunlight to form OH (the hydroxyl radical), which is known as the "detergent" molecule because of its proclivity for reacting with air pollutants and turning them into more benign substances. But on the other hand, ozone is toxic to plants and animals, including people. It is the source of photochemical smog, which is becoming a worldwide problem. And in the upper troposphere, ozone acts as a very efficient greenhouse gas, and may contribute to global warming.

It's difficult to determine how best to address the problem of ozone in the troposphere because the processes of ozone formation and destruction are exceedingly complex, and its global distribution is largely unknown and greatly complicated by the troposphere's turbulent weather systems. TES is helping to fill this important knowledge gap.

Global Warming

Along with ozone, gases such as water vapor, methane, carbon dioxide, nitrous oxide, and fluorine-containing compounds are called "greenhouse" gases because they trap heat and warm the planet's surface. Some of these gases are generated naturally, and some through human activities. The natural greenhouse effect has been good to us, warming the atmosphere near the ground to a comfortable 15°C (59°F) on average. Without it, the average temperature would be closer to -18°C (0°F) and far less hospitable to life.

But the artificial component of the greenhouse gases currently in our atmosphere appears to be carrying this warming effect too far, threatening significant disruption to our climate with consequences to our health, agriculture and, as ice shelves melt and the oceans expand, our coastlines. It could also disturb weather patterns significantly, causing drought or flooding in important farming regions. TES is measuring the gases pertinent to global warming.

The information TES provides on all these issues will help us make choices based on sound science, to the benefit of our country and the world.