Case Study: How Do Carbon Monoxide and Aerosol Concentrations Affect Earth's Atmosphere?

Earth's Dynamic Atmosphere

NASA NEO, Global Aerosol Optical Thickness concentrations acquired using the MODIS sensor, May 2010.
Global Monthly Carbon Monoxide concentrations acquired using the MOPITT sensor, September 2005. Image from NASA NEO.

Anyone who watches the weather knows that Earth's atmosphere is a complex, dynamic system—it is constantly changing. The important questions about our thin, life-sustaining blanket of gases in the 21st century are :

  • How is it changing?
  • What factors and events are driving these changes?
  • What do these changes mean for life on Earth?

What drives atmospheric changes, and why should we care? That's a fair question. After all, humans have evolved, and indeed thrived, in this unpredictable and highly dynamic environment. The answer is this: We should care because human activity appears to be altering Earth's atmosphere at a very high rate. Indeed, recent findings indicate that important components of the atmosphere are changing more rapidly now than at any other time in human history. Because the composition of the atmosphere is so important in regulating conditions on Earth, and we are so totally dependent on those conditions, we need to develop an accurate understanding of how the atmosphere is changing, and why.

Carbon Monoxide, CO

Carbon monoxide is an invisible, odorless, highly toxic gas that is produced through incomplete combustion. Its name is often abbreviated to its chemical formula, CO. Global background concentrations of carbon monoxide range from about 0.05 to 12 parts per million (ppm). The major natural sources of this gas are brush fires, forest fires, and volcanoes. Burning of fossil fuels such as oil, gasoline, natural gas, and coal are the major anthropogenic sources. According to the U.S. Environmental Protection Agency, 60% of the total global emissions of CO are from human activities. Internal combustion engines in automobiles are the largest single producers of this poisonous gas.

Although carbon monoxide has always been a component of Earth's atmosphere, its concentrations have increased since the industrial revolution when humans began using technologies that dramatically heightened the amount of burning that occurs. CO is an important part of the atmosphere because it reacts with other atmospheric compounds to form pollutants that have a negative impact on human health and can potentially influence the global climate system. In sunny urban areas where large amounts of CO are produced, it reacts with other pollutants to form ozone and "smog," both of which are responsible for serious human health problems. At larger scales, CO can impact the global climate system by slowing the rate at which carbon dioxide is removed from the atmosphere. In addition to this reduced removal rate, CO ultimately forms additional carbon dioxide over time, when it reacts with oxygen (O2) in the atmosphere.

Aerosols, Often Called "Particulates"

The skies over Northern India, filled with a thick layer of aerosol particles along the southern edge of the Himalayan Mountains. Courtesy of NASA's Visible Earth Collection.

Aerosols are very different from CO, but also play a role in human health and environmental quality. Aerosols, unlike gases, are solid particles that are very, very small—so small that they become airborne. Once they are in the air, they can travel thousands of miles before settling out in the oceans or on land. Unlike CO, aerosols are not invisible, even though they may be difficult or impossible to see at low concentrations. However at high concentrations, they are easily visible. In certain places and at certain times, such as in the desert during a strong wind storm, aerosols from the dry, dusty soils may become so concentrated as to block out the sun. At lower concentrations, they absorb and scatter less sunlight, but may still be visible.

There are many reasons scientists are interested in aerosols. These include:

  • Monitoring environmental "disturbances" such as forest fires and volcanic eruptions
  • Monitoring air quality for public health
  • Studying the Earth's radiation budget
  • Studying climate change

Discovering and Describing Atmospheric Interactions

In this chapter, you will explore the temporal and spatial patterns of aerosol and carbon monoxide concentrations in the atmosphere to discover and describe the interactions between them. Using satellite imagery, you'll examine these two parameters to discover their origin or source and understand how they influence our changing planet.