July 16, 2014
Ten Years After Launch, NASA’s Aura Mission Keeps On Providing Invaluable Data About Our Atmosphere
April Flowers for redOrbit.com - Your Universe Online
Ten years ago on July 15, NASA launched the Aura satellite aboard a Delta II 7920-10L rocket into a sun-synchronous, near polar orbit approximately 400 miles above the Earth. Aura, which is Latin for "Breeze," has provided a wealth of data over the past decade, including the cause, concentrations and impact of major air pollutants. Aura's four instruments give scientists a comprehensive view of the Earth's atmosphere by measuring various gas concentrations.
In 1968, astronaut William Anders became the first man to orbit the moon. During his flight, he took what has become an iconic photograph of the surreal view of Earth rising above the moon's surface. “We came all this way to explore the moon, and the most important thing is that we discovered the Earth,” Anders famously said. Atmospheric problems were already ramping up on Earth, however, when Anders took his photograph.
Chemical chaos already ruled in the atmosphere. Automobile exhaust and factory pollutants masked the sky. Air pollution in large cities was causing burning eyes and lungs in humans. Acid rain damaged plants and contaminated fresh water. Scientists did not yet understand the extent of the damage, nor did that have a detailed explanation for it. Knowing it was there, however, was enough to push the US government to introduce the Clean Air Act of 1970 in an effort to reduce some pollutants.
In the nearly half a century since, satellite-based observations have helped increase our knowledge of the chemical processes happening in the atmosphere that affect human lives in both the long- and short-term.
Most of us think of the atmosphere as starting far beyond the surface of the planet, but the truth is, it starts at the ground level where we all live and breathe. Air pollution can be seen with the naked eye as a smoky haze that hangs in the sky and blocks the sun's rays. Masses of toxic fog rolled through Los Angeles during the 1940s, shutting the city down for days at a time. Scientists of that time period did not have a deep understanding of the causes and long-term effects of living in those clouds.
As researchers have since learned, the smog in LA is very different from the sulfur-laden smog of coal towns. LA's pollution also contains ozone, which is a pollutant created as a result of chemical reactions in the sunlit atmosphere. Presently, ground-level ozone is not measured by any satellite, but Aura is able to measure nitrogen dioxide, a key ingredient in the formation of ozone.
Human activities such as agriculture and power plant emissions flood the atmosphere with pollutants such as nitrogen dioxide. NO2, a brownish gas that can envelop cities, leads to respiratory problems, especially when it becomes part of ground-level ozone, which can burn the lungs when inhaled.
One of Aura's instruments is the Ozone Monitoring Instrument (OMI), which began monitoring levels of NO2 globally shortly after the satellite was launched. From 2005 to 2001, OMI data has shown a steady four percent a year decrease in NO2 levels in the US. During this time, stricter policies on power plant emissions and vehicle emissions were enacted—resulting in decreased ground-level ozone concentrations. During the same time period in Europe, OMI revealed a 2.5 percent decrease in NO2 levels per year as a result of the same types of legislation.
Though US air quality has continued to improve, there is still a nationwide problem. Unhealthy levels of ozone need bright sunlight to form, making ozone pollution mainly a summer issue.
Studies as recent as 2012 have shown that approximately 47 percent of the US population lives in counties with pollution levels over the National Ambient Air Quality Standards, according to the Environmental Protection Agency (EPA). Ozone levels tend to peak on hot, sunny, windless days.
Air pollution is not an issue solely for the US, the rest of the world suffers from it as well. The World Health Organization (WHO) reported eight deaths in 2012 related to air pollution. OMI reveals increases in NO2 outside of the US and Europe as well. China's NO2 levels, between 2006 and 2010, increased a little over half a percent each year.
“We knew we could measure nitrogen dioxide levels, but I don’t think anyone thought we would be able to actually get quantitative emissions estimates,” said Anne Douglass, Aura project scientist at NASA's Goddard Space Flight Center. “That’s important because in North America and Europe, you have good estimates of how much of a pollutant is going into the atmosphere, but in most of the world, you don’t.”
Sulfur dioxide is another pollutant that presents challenges. The human-produced invisible gas is mainly created through coal-burning and ore smelting. Sulfur dioxide combines with other chemicals to form acid rain or sulfate aerosols that affect health and climate. OMI has identified large concentrations of sulfur dioxide.
Since the EPA passed the Clean Air Interstate Rule in 2005 (which requires 27 eastern states and Washington, DC to reduce air pollutants), OMI has recorded a 40 percent decline in sulfur dioxide concentrations over the largest power plants. Many other countries, however, have not reduced their sulfur dioxide concentrations.
Aerosols, also known as particulate matter, are made up of emissions from various sources, including smoke from burning wood. In the atmosphere, particulate matter can penetrate deep into a person's lungs, cause allergic reactions and infections and increase the risk of heart and lung disease.
Aerosols are also formed from chemicals such as sulfur dioxide and ammonia, which comes from animal waste, fertilizers and soil.. These aerosols can be carried long distances on the prevailing winds. Another of Aura's instruments, the Total Emission Spectrometer (TES), measures ammonia.
“The Tropospheric Emissions Spectrometer measures a lot of constituents that you can’t see like ammonia and agricultural emissions,” Douglass said. “We’re beginning to get ammonia estimates that we did not have before.”
The Aura mission has provided a decade of invaluable data, and sets the stage for future air quality monitoring instruments. OMI's measurements will be continued by the European Space Agency's (ESA) TROPOsphereic Monitoring Instrument, or TROPOMI. TROMPOMI will have better ground resolution, more precisions, and will be able to monitor methane and carbon. NASA also plans a follow-up to Aura. The Tropospheric Emissions Monitoring of Pollution (TEMPO) will observe ozone, nitrogen dioxide, sulfur dioxide, formaldehyde and aerosols with higher ground resolution and frequency over the United States, Canada and Mexico.
“Pollution is a global issue because it can travel long distances in the wind,” said Douglass. “By using satellites, we can develop a valuable global inventory of pollutants and understand how air quality may be changing.”