Atmosphere | Aerosols | Natural & Man Made

Dust and aerosol plumes often blow from Africa into the Atlantic in the spring. They cover thousands of square miles and transport tons of particles. They reach to the forests of Brazil and the Caribbean islands. They have been linked to pollution alerts, soil quality in Brazil, and impact on coral reefs. Images from NASA.

The dust and aerosols plumes also arrive from Asia. Prevailing westerlies in the middle latitudes brings tons of particles from China and other countries. Here is an image of a common situation over China. The land mass is obscured from view due to dust and aerosols, in addition to the clouds. Cloud formation is enhanced by particles in the atmosphere. They provide nucleation centers for water droplet formation, hence clouds.

Measurements have been made of the tiny airborne particles that arrive by air in North America each year according to NASA and university researchers. At least 64 million tons of dust, pollutants, and other particles mix into the air over North America each year. Over 69 million tons of aerosols are produced within North America alone by natural processes, transportation, and industrial sources. This new estimate of airborne aerosols nearly equals our own domestic production according to this study published in Science.

April 11, 2010

The study estimated that dust from Asia makes up 88% (56 million tons) of the particles reaching North America. These images show modeled dust moving from Asia to North America in April 2010. Credit to Goddard Earth Observing System Model, Version 5 (GEOS-5). Note the density of the model in central China near the Taklimakan Desert. Aerosols are carried by large dust storms usually in the spring. In addition, North America receives many aerosols from Africa and the Middle East.

April 14, 2010

Aerosol data came from instruments on the Terra satellite and the Cloud-Aerosol LIDAR and Infrared Pathfinder Satellite Observations (CALIPSO) satellite. CALIPSO provides high-resolution vertical profiles of aerosols and clouds. Below is an example of a vertical profile from CALIPSO as it passed over a fire region in Arizona in 2011. The satellite uses LIDAR, light detection and ranging. It is similar to radar but employs light instead of microwave energy. The LIDAR measures the thickness and composition of clouds and aerosol layers and their altitudes.

Significance of the Findings

Scientists are beginning to quantify how many airborne particles reach North America. Determining their impact on warming or cooling the planet is one of the most difficult challenges in climate science.

“This is a crucial step toward better understanding how these tiny but abundant materials move around the planet and impact climate change and air quality,” says Hongbin Yu, lead author and an atmospheric scientist at the University of Maryland and NASA’s Goddard Space Flight Center.

Yu and colleagues observed different particle types and their heights in the atmosphere. That information along with upper atmosphere wind speed data allowed them to estimate the amount of pollution and dust arriving in North America. Dust and pollution particles rise into the atmosphere and can travel for days before settling to Earth. In doing so, they cross many political boundaries.

According to the research, about half of the particles above North American come from someplace else. They come in from high in the atmosphere. And, most of it is dust, not pollution, from sources in other countries. This has important implications for international treaties and agreements about pollution and its passage from nation to nation. Turning off all industry in the nations of the world would still leave us with a large amount of aerosol particulates because it is a larger naturally occurring process than was realized before.

This 3 minute video summarizes the findings and contains some commentary by the scientists involved. It tells of some of the impacts that aerosols have on weather and climate.

What are Aerosols?

About 90 percent by mass, most aerosols have natural origins such as volcanoes, forest fires, and certain plants. Some plants can produce gases that react with substances in the air to cause aerosols such as the “smoke” in the Great Smoky Mountains. Ocean micro-algae produce a sulfurous gas called dimethylsulfide that turns into sulfate aerosols in the atmosphere. Sea salt and dust are two of the most abundant aerosols. Sandstorms blow mineral dust from deserts into the atmosphere. Ocean waves send sea salt aloft. Both of these sources make particles which are typically larger than man-made aerosol particles.

Some common sources of aerosols and dust particles.

Salt, Dust, Soot

Micrographs – USGS, UMBC, ASU
(L to R) Western Sahara Project, Jonathan Jessup, Vox, and Ludie Cochrane

About 10 percent by mass of aerosols are man-made. They are common in the air downwind of urban and industrial areas. Burning fossil fuel makes large amounts of sulfur dioxide that reacts and makes sulfate aerosols. As people clear land and burn off the biomass and organic waste, it makes smoke with a lot of organic carbon and black carbon soot.

What Are Some Implications?

• We don’t fully understand how aerosols affect climate. This study estimates that aerosols from overseas may result in one third of the total solar radiation reduction in North America. Aerosols and clouds seeded by them reflect about a quarter of the Sun’s energy back to space. It also says dust and pollution can change atmospheric circulation patterns. These changes impact weather and climate. How these changes occur and their impacts requires further study. More discussion of these impacts can be found in this link.

• Dust and pollution aerosols can ‘seed’ clouds. This affects rainfall and snowfall patterns. The tiny particles act as a nucleus, or seed, for water droplet formation, or snow flakes. More particles are thought to increase precipitation by this seeding.

• Dust and soot particles land on snow and cause it to become darker and melt sooner. This has implications for the quantity, quality, and timing of our water supplies.

• Changes in weather and climate affect how pollutants get mixed and removed by the atmosphere. A robust modeling system is needed to assess the climate and air quality implications of these new findings.

• Most of the aerosols that cross the Pacific Ocean are high in the atmosphere, and not in the air that we breathe. Only about 5% of that dust enters the continent within the lowest 1.2 miles (2 kilometers) of the atmosphere. So air quality implications may not be significant. The researchers believe controlling pollution near the surface is a more effective way of controlling the health effects of aerosols in our immediate surroundings.

According to Dr. Hongbin Yu …

There has been concern about an emerging Asian economy and the increased pollution that will influence North American air quality and climate. But we found that dust makes large contributions here. So we cannot just focus on pollution. We need to consider dust.

The take-home message is that this is a small world and we share one atmosphere. Every country is influencing other countries’ back yards.



20 thoughts on “Atmosphere | Aerosols | Natural & Man Made

  1. Immediately, I wonder if solutions similar to what was done in the video clip might also be effective in combating these factors of climate change. I could just link you to the YouTube video but I discovered it on another fellow blogger’s site and want to give her credit for the share. By the way, If you check out her blog, I think you may find some of it right up your alley…even more so than mine.

    Now, as comparison…look at the cause and effect of what excessive plowing did to the US during the Dust Bowl…and how much of the US must have traveled to other continents at that time.
    I think it is worth the time and energy to locate what environmental factors would created the greatest change (improvement), thus modifying temperatures and winds in order to tip the scales back closer to normal.

    We build, build, build without looking at the global impact. If we can’t change the way people behave, perhaps we can alter the way nature behave…in our favor.


    • The problem with using methods to control the local climate is that it is difficult to predict how these solutions may work and where they will have an impact. Houghton’s “Global warming, the complete briefing” is a good book to read on the topic climate change. I believe that we have tinkered enough with the climate that we cannot afford to add more unknowns into the equation. Best way to cure the patient is not to put a band-aid on the patient but to take away the cause.


    • I will check out that blog this morning.

      I watched the series last year about the dust bowl. What an awful mess that was. The land was fine. Nature had the best adapted plants in the soil. Then, people stepped in to sell it as something it wasn’t. It collapsed and blew away.

      I don’t think I want to try to engineer nature to behave differently. It finds ways to change in response to whatever we do. I’m afraid we might end up with an even worse situation.

      Thanks for your good comments.


  2. I followed your nucleation link and found the article there very interesting. I get the impression from the article as a whole that the interrelations among the weather phenomena mentioned there are so complicated that no one really knows what’s going on.

    The last part of the article, about phytoplankton, particularly caught my attention with its two opposing hypotheses. That section said that “no conclusive evidence to support” the so-called CLAW hypothesis, with its prediction of a stratified ocean and a decline in phytoplankton, exists. In contrast, the article said this about the contrary hypothesis: “The idea that an increase in global temperature would also increase phytoplankton activity and therefore CCN numbers was seen as a possible natural phenomenon that would counteract climate change. An increase of phytoplankton has been observed by scientists in certain areas but the causes are unclear.”


    • Yes, the systems of the oceans interfaced with the atmosphere are varied and complex. If the two fluids were stationary, that would be complex enough. But, they each flow freely. Finding a cause and effect relationship is really hard.

      My opinion about the increase in cloud cover from nucleation is it would lead to a warmer, not cooler planet. I see it as a Venus runaway greenhouse effect. But, I’m guessing.


  3. The thing that struck me most is how many tools and instruments we have available for research into these topics. Just the number of satellites up is astounding. Those who claim we don’t have evidence enough to draw any conclusions must be stuck somewhere 60 years ago, when in fact we did not.


    • I agree. Sorting through the large amounts of data is challenging. The systems in the atmosphere and the oceans are varied and complex. Exact cause and effect relationships are hard to pinpoint. But, the evidence is strong showing the impact we have upon the Earth.


  4. This interesting post leaves me rather disappointed that scientists haven’t made better progress in understanding the Earth’s climate as a system (singular). Clearly, that system is made up of complex components like cloud albedo, ice mass, ocean currents, biomass gasses, and so forth. But, I’m thinking that the weather has been stable enough for some form of life to exist on the Earth for more than 3 billion years. Conclusion: excluding non-man-made effects, the climate system is stable (in the engineering sense) within the bounds required for life. That implies it is somehow self-correcting over time, otherwise it would have crashed like the atmosphere of Venus. Three billion years is a long time: 3,000,000,000.

    I’m glad they are studying the albedo effects because it strikes me that this could be an important way to reverse global warming if human sources have, as I suspect, pushed the climate system out of its long-time comfort zone.


    • Agree, it is frustrating. It speaks to the complexity of two dynamic and fluid systems. We are getting closer to better understanding. But, what a long way to go.

      What a monumental thing it would be to find a way to reverse global warming. Who would get to be ‘in charge’ of that effort? Can it be weaponized? Is there profit to be had?

      My skeptical genes are showing.


      • “Who would be in charge?” Good question. I suppose it would have to be a UN-style effort. I used to be skeptical of the value of the UN, but I’ve come to see it as the only viable means to cooperation among nations. There have been successes of course, including a world-wide vaccination program, disaster relief, and the ISS. The newly inaugurated giant ALMA radio-telescope, a $1.5 billion dollar project in Chile, also demonstrates multinational collaboration. Who’d a thunk?


      • Yes, the organization isn’t perfect. But, it does do some very good things. The intentions are positive and meant to be helpful.

        I know about the ALMA project. I have a post about it in fact. It is quite impressive and beginning to produce some observations.


  5. Meanwhile, speaking of dust, the word of the day in the Texas Panhandle is “haboob” , and it’s heading south. It’s gusting to 55 in Amarillo right now, and visibility is close to zero because of the dust.

    Another interesting dust tale. When I was in Liberia, I often got to fly to the farthest-flung clinics. The hospital had a Cessna STOL, and the “airstrips” were hacked out of the bush with machetes.

    The pilot had been there for years — decades — and had learned to read the dust. When the harmattan winds blew from the Sahara or other portions of north Africa, he could tell you were they were blowing from by the color of the dust on the plane when we landed. I’ve seen pink, yellow, gray, white – all quite different from our normal laterite red. He kept exquisitely detailed daily records, and was able to predict seasonal wind shifts as well as note anomalous events that others missed.

    And, dust from the Sahel often influences tropical systems coming off the African coast — the so-called Cape Verde storms. It’s fascinating to watch the interaction of dust with a developing storm.


    • Those are great observations. Local knowledge of the dust and the winds is invaluable. There are so many intricacies like those all over the world. I guess that is why understanding and modeling it for the sake of prediction is so challenging.

      Thanks so much for those comments.


  6. No borders in the atmosphere, and these damaging aerosols, even tracked from specific origins, demonstrate the need to think and act globally. Besides the particulates from Chinese industrial pollution affecting climate in my Pacific NW home, I’m especially concerned about the dust from North Africa – increasing with long term drought due to climate change and overgrazing – falling on the already stressed reefs of the Caribbean. The iron and pathogens in African dust falling from the sky are impossible for local jurisdictions to deal with. These global satellite programs can be very helpful as a source of information at least. Thanks for describing the breadth of their potential.


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