We recently received this question from Jeff, a reader in Colorado:

We’ve been having lots of hazy days in Colorado. I’m sure it’s common over most of the U.S., Alaska, Canada, and Greenland. Most likely, it’s also over Europe.

I saw your images of fires burning in Russia. Could it be that a lot of our haze in the western U.S. and beyond, is due to these fires? I realize there are also many fires burning in the lower 48 states at this moment.

Would you be able to post information concerning the vast amount of smoke and pollutants that are now being created by mankind, and how that is directly affecting the process of climate change.

Jeff’s first question is one that air quality officials ask routinely. Is the pollution over my city from local sources that can be regulated, or does it come from somewhere else? Summer pollution can have many sources, both local and distant.

I sent the question to Gabriele Pfister, researcher at the National Center for Atmospheric Research in Boulder, Colorado. Gabriele has investigated how smoke travels and what impact it has on air quality far from the fires. She replied:

Around the world, ash and thick smoke from wildfires can fill the skies. While the smoke seems to disappear with distance from the fires, polluting gases and small particles that are invisible to the human eye can be carried away by global air currents. Over the past decade, satellite data helped reveal that pollution transport often occurs over hundreds and even thousands of miles, and long-distance transport has received increased attention due to the potential impact on the air quality of continents downwind.

Wildfires release a range of chemical species to the atmosphere, similar to pollutants emitted from human sources. These include the greenhouse gases carbon dioxide and methane, but also other air pollutants such as carbon monoxide, nitrogen oxides, volatile organic compounds, and aerosols. The gaseous pollutants also influence tropospheric ozone formation, a pollutant as well as a potent greenhouse gas.

Research on the transport of pollutants in the troposphere indicates that air pollution is not a local but a global problem. A good example for this is a study by Pfister et al. on the extreme wildfires that happened from June through August 2004 in Alaska and Canada. These fires produced approximately 30 teragrams of carbon monoxide, roughly equal to all the human-generated carbon monoxide for the entire continental U.S. during that same period. Using satellite data and models, researchers estimated that ground-level ozone increased by up to 25 percent in the northern continental United States, and by up to 10 percent in Europe.

So, could Russian fires be causing hazy days in the United States? Let’s take a look at some satellite measurements. This image shows carbon monoxide, one of the constituents of smoke, in July 2011. Carbon monoxide is not visible, but it can combine with other pollutants to contribute to urban haze. It is also a harmful pollutant on its own.

The image was made with data from the MOPITT sensor on the Terra satellite. High concentrations of carbon monoxide are red and lower concentrations are yellow. (Regularly updated images are on the NEO web site.)

The Russian fires burned throughout July, and clearly they produced a lot of carbon monoxide. Carbon monoxide may also be coming from industrial processes in eastern China. Carbon monoxide concentrations are high across the North Pacific and into North America. Some of the gas over North America may be from the Russian fires, but intense fires in Canada probably contributed much more to air quality in the United States.

One of my favorite resources for tracking pollution in the United States is the Smog Blog. They have several posts discussing the Canadian smoke over the United States in July.

Jeff’s second question—how is pollution directly affecting Earth’s climate—is among the most important questions in climate science at the moment. The greenhouse gases released from fires will accelerate global warming. However, most pollutants act like a shade that cool the Earth by reflecting energy back into space. The exceptions are black carbon or soot particles, which absorb energy and make the atmosphere warm up while the surface cools. See Aerosols: Tiny Particles, Big Impact.

On the other hand, pollution has a few indirect impacts on climate. When particles settle on snow or ice, dark-colored pollution causes that surface to absorb energy rather than reflect it. This results in additional warming.

Pollution also affects clouds in a variety of ways, and clouds have a huge impact on global climate. In some cases, pollution causes clouds to be brighter and reflect more energy, causing cooling. In others, pollution can suppress the formation of clouds. Since clouds reflect energy and cool the Earth, the absence of clouds would cause warming. Right now, scientists don’t know exactly how the interaction between clouds and pollution will influence the climate.

We can be pretty sure, however, that global warming will impact pollution. Here’s what Dr. Pfister said:

About half of the world’s air pollution comes from wildfires, and a bad fire year can result in pollution from the fires circling the globe. Global warming is expected to cause earlier snowmelts, hotter temperatures, more frequent droughts, and more frequent and more potent fires. (Actually, this is already occurring.) And these fires release even more pollutants and greenhouse gases into the atmosphere that in turn might result in even hotter and drier weather and more fires.

Great question, thanks for writing Jeff!

This entry was posted on Thursday, August 25th, 2011 at 4:58 pm and is filed under Uncategorized. You can follow any responses to this entry through the RSS 2.0 feed. Both comments and pings are currently closed.