Oxygen, or O2 on the table of chemical elements, is a vital component for life on Earth. It is the second most abundant gas in Earth's atmosphere, making up about 21 percent of its volume. On the other hand, its cousin ozone (O3) makes up less than 0.00001 percent. In fact, if all the ozone in Earth's atmosphere were brought down to the surface, air pressure and temperature conditions would compress ozone into a layer just three millimeters thick, equivalent to two pennies stacked one on top of the other. ! Despite its tiny amount, ozone is also a vital ingredient for life on Earth.
Ozone in fact is vital for life on Earth, but it also has a "bad" side as well - that is, there is both good and bad ozone out there. Good ozone, which accounts for about 91 percent of the ozone in Earth's atmosphere, is present in the stratosphere, the middle layer in Earth's atmosphere. This portion of ozone is commonly referred to as the "ozone layer." The ozone layer absorbs more than 90 percent of the sun's high-frequency ultraviolet light, which is potentially damaging to life on Earth. Without the ozone layer, this radiation would not be filtered as it reaches the surface of Earth, resulting in detrimental health effects for life on Earth. Among the health effects humans could experience as a result of overexposure to ultraviolet radiation are skin cancers, premature aging of the skin and other skin problems, cataracts and other forms of eye damage, and suppression of our bodies' immune systems and our skin's natural defenses.
The troposphere, the part of the atmosphere closest to Earth, contains both good and bad ozone. In the lower troposphere, ozone may serve as an air pollutant since it is a major component of photochemical smog. In the middle troposphere, ozone acts as an atmospheric cleanser, and in the upper troposphere, ozone is a greenhouse gas, which could be bad if concentrations get too high.
The Tropospheric Emission Spectrometer, a science instrument onboard NASA's Aura satellite, is improving our understanding of the good and bad ozone in the troposphere. The spectrometer, which was launched in 2004, provides the first global view of tropospheric ozone and vertical concentrations of ozone, as well as temperature and other important tropospheric features, including carbon monoxide (CO), methane (CH4), water vapor and ammonia (NH3). The instrument has studied the origin and distribution of tropospheric ozone. It has also shed light on how the increasing ozone abundance in the troposphere is affecting air quality on a global scale, as well as ozone's role in chemical reactions that "clean" the atmosphere, and climate change.
These data are used by scientists to determine the degree to which natural sources, like lightning and plant growth, and human-produced sources, like automobiles, industrial pollution, and biomass burning, contribute to ozone production and chemistry. For example, during summertime in the upper troposphere, where ozone acts as a greenhouse gas, lightning generates much greater amounts of ozone than do human activities, thereby having a big impact on regional pollution. Over the last few years, the spectrometer has obtained global data on ozone and chemicals that participate in ozone formation. The fact that the instrument is able to quantify vertical profiles of ozone improves our understanding of how various reactions taking place at specified heights contribute to ozone chemistry. Similar to ozone, chemicals that participate in its production also exist in tiny amounts. Still, this enables scientists to better understand long-term variations in the quantity, distribution and mixing of many tropospheric gases that have a large impact on climate and air quality.
My role with the instrument is to validate the quality of the most recent ozone measurements, which are taken in a special observation mode, called "stare." This mode is used to monitor biomass burning events and volcanic activity. I compare measurements taken by an ozonesdone (a lightweight, balloon-borne instrument that measures ozone, air pressure, temperature and humidity as it ascends through the atmosphere) with measurements from the tropospheric spectrometer. We do this so we can demonstrate the accuracy and precision of the instrument's readings. I am also participating in projects that use the instrument data to better understand the chemistry and transport of pollutants coming from wildfires, such as those that occurred in Australia in December 2006. For the future, I am interested in using the tropospheric spectrometer satellite data for ozone and methane to better quantify the degree to which they contribute to global warming and climate change.
Remember the warning to beware of yellow snow? Well, what’s true in your backyard is true on a much larger scale too. (For those from warmer climates, yellow-tinted snow is a sign that a dog or other animal has recently “paid a visit.”)
Snow at Earth’s north and south poles can also be tainted. Certain molecules — ones that can eventually damage our protective ozone layer in the stratosphere, affect the air down in the troposphere where we live, and possibly contribute to climate change — are being deposited into the snow.
Just how is this happening? Start with the fact that air at lower latitudes circulates toward the poles. This air carries ozone-damaging molecules picked up in industrial, highly populated areas. Once over the poles, some of these molecules are deposited onto the snowpack, where they migrate to thin liquid films in snow. Once sunlight hits the snow, the light energy breaks down these molecules, which are then released back into the atmosphere, giving the area over the poles a double hit of ozone-damaging molecules.
Scientists are finding that snow has unique properties that make these chemical reactions happen much faster than we used to believe. We don’t fully understand why this is happening, but we know that the mixture of sun (an energy source) and snow bring about the release of these ozone-damaging molecules into the atmosphere much faster than in areas without snow.
Many of the polluting molecules that remain in the snow eventually get incorporated in the polar food chain. When the snow melts into the sea, the molecules may be ingested by sea creatures. Not all of them are unhealthy, but some of them are.
Why care about reactions going on in distant, frozen expanses at Earth’s poles? Those regions are a beacon of climate change, where we see chemical processes that may play a large role in the planet’s future.