Tag Archives: air quality

AGU2011: How Satellites Can Fill the Gaps in Air Quality Maps

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You’ve most likely seen color-coded, real-time AIRNOW maps of air quality on the web or on television that show whether the air is safe, unhealthy, or hazardous. What you may not realize is that the network of ground-based instruments the EPA uses to make those maps has large gaps in some parts of the country, particularly in sparsely populated areas of the Great Plains and Intermountain West. (Red in the map above indicates areas without ground monitoring stations;  black dots show the locations of stations).

To address this problem, an effort sparked by recent advances in satellite measurements of air pollution seeks to integrate NASA and NOAA satellite measurements into the AIRNOW system. The accuracy of satellite measurements of air quality can vary depending on the weather, the topography, the brightness of the underlying surface and other factors, so the researchers leading the effort are developing a method that selectively incorporates only the reliable satellite data. The researchers are still refining the technique and the system isn’t yet operational, but preliminary case studies suggest the technique will be up and running by 2013.

The figure above shows the technique researchers are developing tofuse ground observation and satellite observations of the small particles (PM2.5) that causes health problems. Groundobservations have high uncertainties (shown in the darkest blue) indifferent areas than the satellite observations. The right combinationof the two – see the fused maps at the bottom of the figure – will be more accurate  than either the ground network or satellite measurements alone.

Text by Adam Voiland. AdamPasch of Sonoma Technology presented a poster about this topic at theAmerican Geophysical Union fall meeting in San Francisco on Dec. 5, 2011. Video producedby Sonoma Technology. Imagery courtesy of Adam Pasch.

AGU2011: What Would Pristine Air Mean for the Climate?

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Imagine that all the aerosols (the miniscule particles of pollution, dust, sea salt, and many other things) floating around in the air over the United States suddenly disappeared. What would their absence mean for the climate? Loretta Mickley, a climatologist and aerosol expert from Harvard University, has tackled just that question by running a series of simulations with a high-resolution computer model developed at NASA’s Goddard Institute for Space Studies.

Her conclusion: the elimination of the particles would increase ground temperatures across the eastern United States, cause more springtime rain to fall, and drive an uptick in heat waves. All of this would be driven by something scientists call the “direct effect” of aerosols – the particles’ ability to warm or cool the atmosphere by either absorbing or scattering incoming energy from the sun. (In this case, the model didn’t account for the “indirect effects” of aerosols – how the particles affect clouds, a detail that can have an impact on how they affect the climate as well).

Atmospheric Environment published a study that details the experiments in July of 2011. Here’s how Mickley summarized the findings:

We find that removing U.S. aerosol significantly enhances the warming from greenhouse gases in a spatial pattern that strongly correlates with that of the aerosol. Warming is nearly negligible outside the United States, but annual mean surface temperatures increase by 0.4-0.6 K in the eastern United States. Temperatures during summer heat waves in the Northeast rise by as much as 1-2 K due to aerosol removal, driven in part by positive feedbacks involving soil moisture and low cloud cover. Reducing U.S. aerosol sources to achieve air quality objectives could thus have significant unintended regional warming consequences.

There’s good reason to consider how falling levels of aerosols will affect the climate. In the United States, several kinds of aerosol particles have actually seen their numbers fall steadily as regulations have gone into place to clean up the air for the sake of public health. Emissions of sulfur dioxide, for example, a gas produced by coal power plants that generates reflective sulfate particles has fallen by 83 percent since 1980.

Mickley presented her poster on Monday, Dec. 5, 2011. Text by Adam Voiland. Aerosols panel (from left to right:ash, pollen, sea salt, soot) published originally by NASA’s Earth Observatory. Lowerfigure courtesy of Loretta Mickley. 

What on Earth is That? #1

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(Please post your guesses and your name in the comments, and we’ll give the answer next week…)

Here at What on Earth, we’re constantly stumbling across interesting photos, videos, and audio clips from NASA’s exploration of our planet (be it from space, the field, or the lab.) Whether it’s a satellite montage captured from thousands of miles up, the roar of our B-200 research aircraft, or a microscopic view of a cloud droplet, there’s literally always something strange and wonderful passing across our desks.

To have a little fun (and spare all that fascinating stuff from the circular file), we’re going to post snippets of it every now and then, usually on Fridays. What we post will change, but the question to you all will always be the same: “What on Earth is that?

Our only hints:

  • Our picks will always be related to Earth science in one way or another, and…
  •  It will have some relation to what we do at NASA.

We’ll give you a week to post your guesses, and we’ll post the answer the following Friday.


Updated 7/16/2010

So, what on Earth was that? We received a barrage of thoughtful—and creative—responses that ranged from pollen, to DNA, to carbon nanodiamonds embedded in Antarctica ice. Ant-related answers were surprisingly common. (Nope, it isn’t an ant eating salt, spitting up acid, or laying eggs.) It is, drum roll please, a microscopic view of soot from wildfire smoke in Africa. Congratulations to posters MicroMacro (comment 121), Arbeiterkind (comment 124), Mike (comment 125), Michael & Marion Dreyer (comment 130), and Rosemary Millham (comment 141), who were correct or on the right track. A more complete description of the aerosols from this particular fire, including the image above, was published in the Journal of Geophysical Research (account required).

Here are a few more details to impress your pals: Bits of soot (a type of aerosol particle) tend to clump together into the chain-like structures visible above. Wildfires, diesel trucks, factories—anything that partially burns the carbon locked away in fossil fuels and organic materials can produce soot and release it into the air. Soot makes doctors nervous as it can cause health problems when it lodges in our lungs and works its way into our bloodstream. And climatologists are wary of the particles as well because they absorb the sun’s energy and hasten global warming and climate change by heating the atmosphere directly or coating the surface of glaciers. In recent years, black carbon is an active area of research in climate science, and it’s a target of study for a number of NASA’s Earth science projects, including the forthcoming Glory satellite

Image(left) from Peter Buseck, Arizona State University. Image(right) from Jim Ross, NASADryden Flight Research Center.

–Adam Voiland, NASA’s Earth Science News Team

Humisery 2011: No Ordinary View of Air Pollution

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A video camera on board NASA’s P-3B aircraft captured this vertigo-inducing view of Baltimore’s suburbs as part of an air pollution-monitoring mission called Discover-AQ. The P3-B, loaded with multiple pollution sensors, has been cruising along major transportation corridors in the Washington-Baltimore metro area and flying spirals over six ground stations throughout July. Meanwhile, a smaller aircraft, a UC-12, has been flying along the same approximate flight path but at higher altitude of about 26,000 feet. View the animation below to see the flight paths of both planes.

The goal of the flights is to help piece together a more accurate view of the vertical distribution of air pollution by looking simultaneously at the same pollution events with ground, aircraft, and satellite instruments. Flights for this summer will wrap up by July 29th.

The researchers involved in the project haven’t had time to rigorously analyze the data their instruments have collected and publish findings in peer-reviewed science journals yet, but many have posted raw results from the various instruments on Discover-AQ’s science website.

I paged through many of the daily reports and found quite a number of intriguing nuggets of information. For now, though, I’ll share just one set of images – a comparison of particulate pollution levels on July 1 with levels on July 22nd. The data comes from the High Spectral Resolution Lidar (HSRL), a sensor on the UC-12 that uses a radar-like laser technology called lidar to map the distribution of small particles of pollution. HSRL generates data “slices” that show the vertical distribution of the particles, known generally as aerosols, from ground level up to eight kilometers. 

July 1 Flight
(minimal particulate air pollution)

July 22nd Flight (heavy particulate air pollution)

In the HSRL data readouts, high levels of aerosols are shown in red and yellow, while lower levels of particles are shown in blue. On the first day of science flights – July 1st – temperatures were moderate and aerosol levels were low. By the tenth flight, the mid-Atlantic was in the midst of a brutal heat wave (which the Star-Ledger weather team want to call Humisery11), and both ozone and particulate counts from ground stations had shot up.

The HSRL slices capture the difference between clear and pollution-laden skies beautifully. The first flight shows just moderate levels of ground-level pollution – the yellow band in the image below that reaches up to about 3 kilometers. In contrast, the flight on the 22nd, a day that temperatures in Baltimore hit 105 °F, shows a deep red swath of particle pollution near the surface.

HSRL data can be a little confusing to make sense of when you first see it, so realize that scientists plot the data out in a horizontal strip with the passage of time on the upper x axis (the numbers with the UT units) and the latitude and longitude on the lower x axis. Altitude is shown on the y-axis. The two images below should help you see how the strips of data relate to the trapezoidal flight paths

July 1st Flight

July 22nd Flight

Text by Adam Voiland. Flight video from P3-B camera. Flight path visualization from the SVS. Data charts from the July 1st and July 22nd HSRL flight reports.

Has Sulfate Pollution from Asia Masked a Decade of Warming?

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Warming overwhelms the cooling effect of sulfates by about 2045 even if China and India continue to grow rapidly and delay pollution controls. Radiative forcing is a measure of influence that a climate factor has in altering the balance of Earth’s incoming and outgoing energy. Positive forcing tends to warm the surface, whereas negative forcing tends to cool it. A more detailed definition of radiative forcing is available here.

Science News
, the Washington Post, and Climate Central have all written about a new study, published this week by the Proceedings of the National Academy of Sciences, that suggests a decade-long lull in global warming, which has caused some commentators to question the scientific underpinnings of climate change, stems from large increases in sulfur dioxide emissions in Asia.
Between 2003 and 2007, global sulfur emissions have gone up by 26 percent. In the same period, Chinese sulfur dioxide emissions have doubled.

While burning coal is best known for emitting carbondioxide, a greenhouse gas, the sulfur dioxide the same process generates leads to the formation ofreflective sulfate particles that have the opposite effect on the climate. Releasing sulfates might seem, then, like a reasonable way to counteract global warming, but there’s a catch. Sulfates also cause acid rain and health problems. The World Health Organization estimates that air pollution, including sulfates, causes as many as 2 million premature deaths each year.

The combination of the contradictory coal burning impacts leaves policy makers in a bind: clean up the sulfates and accelerate the pace of global warming or allow sulfates to build up and people will die directly of air pollution. Reducing sulfate is relatively cheap and the health benefits don’t take long to realize, so most industrialized countries end up adopting pollution controls that reduce sulfate emissions. The United States, as well as industrialized European countries and Japan, cut sulfate emissions significantly in the 1970s and 1980s, and there’s little reason to believe that China will follow a different path.

In fact, the Chinese government is already in the midst of an effort to reduce sulfate pollution. A team of researchers, including NASA Goddard’s Mian Chin, used satellite imagery and other data about emissions to estimate sulfate emission trends in China in a 2010 paper published in Atmospheric Chemistry and Physics They found that sulfur dioxide emissions increased dramatically between 2000 and 2005, particularly in Northern China. But they also found that sulfur dioxide emissions in China, which I wrote about in an earlier post, began to decline in 2006 after the government began installing large numbers of flue-gas desulfurization (FGD) devices in coal power plants.

Since 2006, flue-gas desulfurization (FGD) devices in coal power plants have caused sulfur dioxide emissions from power plants in China to begin declining.

What does it all mean for the climate? In 2010, Drew Shindell and Greg Faluvegi of NASA’s Goddard Institute for Space Studies simulated a number of emission scenarios for China and India to find out. They looked, for example, at how the climate would respond if the Chinese and Indian economies continue to expand rapidly or only grow at a moderate pace. Likewise, they modeled what would happen if China and India instituted sulfate pollution controls immediately or waited a number of decades before doing so.

In their paper, Shindell and Faluvegi present their results, shown in the line graph at the beginning of this post, as a suite of projections. The strength of warming predicted depends on whether the economies continue to grow quickly and whether sulfate pollution slows, but there is one common – and concerning – similarity between all of the projections: regardless of how fast China or India grow or put off sulfate pollution controls, it’s not enough to mask warming from carbon dioxide in the long term, particularly in the mid-latitudes of the Northern Hemisphere where the climate impacts of sulfates from Asia are the most noticeable.

Here’s how the GISS authors explained the situation:

We find that while the near-term effect of air quality pollutants is to mask warming by CO2, leading to a net overall near-term cooling effect, this does not imply that warming will not eventually take place. Worldwide application of pollution control technology in use in Western developed countries and Japan along with continued CO2 emissions would lead to strong positive forcing in the long term irrespective of whether the pollution controls are applied immediately or several decades from now. Continued emissions at current (year 2000) pollutant and CO2 levels may have little near-term effect on climate, but the climate ‘debt’ from CO2 forcing will continue to mount. Once pollution controls are put into place as society demands cleaner air it will rapidly come due, leading to a “double warming” effect as simultaneous reductions in sulfate and increases in CO2 combine to accelerate global warming. The only way to avoid this would be not to impose pollution controls and to perpetually increase sulfur-dioxide emissions, which would lead to a staggering cost in human health and is clearly unsustainable.

Text by Adam Voiland. Imagery first published in Atmospheric Chemistry and Physics.  

Marylanders: Stop and Smell the Air this July as NASA Planes Buzz Overhead

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Have you ever stopped to wonder why urban air can taste like singed rubber one day and crisp mountain air the next? Or what happens to all those delectable clouds of who-knows-what flowing from factory smokestacks and vehicle tailpipes? Or what makes a blanket of dense smog shroud a city skyline on certain days?

Raymond Hoff, an air pollution expert based at the University of Maryland, Baltimore County, sure has. Hoff has studied air pollution for more than three decades researching topics ranging from Arctic haze, to ozone-damaged beans on the banks of Lake Ontario, to the river of fumes that emanate from Interstate 95. He’s authored dozens of journal articles and book chapters, uses lasers to measure air pollutants, edits a blog about smog, and has led or participated in nearly two-dozen field experiments around the world. 

We caught up with Hoff to find out more about his involvement in a new project – a NASA-sponsored aircraft campaign called DISCOVER-AQ that will help fill in gaps between satellite measurements of pollution and data from ground-based stations. As part of the campaign, NASA will fly a large aircraft – a 117-foot P-3B – on low-altitude flights near major roadways.

What is your role in DISCOVER-AQ?
I manage a ground site at the University of Maryland, Baltimore County (UMBC) that will be part of the campaign. At UMBC, we use lidar, a type of laser, to create vertical profiles of pollutants in the atmosphere. We plan to make lidar measurements at the same time that NASA satellites and aircraft fly overhead and measure pollution from above. The idea is that the ground stations will help validate the satellite and aircraft measurements and give us a more accurate three-dimensional view of air pollution.

What are the main pollutants that you’ll be focusing on during the campaign?
In the summer in Baltimore, there are two pollutants of importance – ozone and particulate matter. Both can cause health problems. On bad air days, we see increases in the number of asthma incidents, cardiopulmonary problems, and heart attacks.

  Baltimore skyline on a clear day.                                                      
Baltimore skyline on a hazy day.   

Where does ozone come from?
Sunlight reacts with certain pollutants – such as nitrogen dioxide, formaldehyde, and other volatile pollutants – in a long chain of reactions to produce ozone. Combustion engines, power plants, gasoline vapors and chemical solvents are key sources of the precursor gases.

What about particulate matter?
There’s a range of particulate in the air. In Baltimore, about 30 to 60 percent of the mass of particles in the air that we worry about are sulfates – small particles generated by emissions of sulfur dioxide. Coal-burning power plants, smelters, industrial boilers and oil refineries release most sulfur dioxide. The other 30 to 60
percent, depending on the day, is usually organic particles. Organics come from vehicle exhaust, evaporating paints, and various commercial and industrial sources. Vegetation also produces a significant amount of organics. The remainder is usually a mixture of dust, sea salt and nitrates. 

Is that a fairly typical mixture of pollutants?
Yes, for a large cities along the Mid-Atlantic and in the Northeast. There are certainly regional differences. There are fewer sulfates in California, for example, because they cleaned sulfur out of their fuels. You see more dust in the West, more organics in the Southeast. You see high levels of certain industrial pollutants over cities like Houston where you have a robust petrochemical industry.

Is most of Baltimore’s pollution local or does it blow in from elsewhere?
We think about half of it comes in from the west over the Appalachians. Some of it comes up from Washington, and some, of course, is local.

Tell me something interesting about air quality in Baltimore.
The role of the Chesapeake Bay and the “bay breezes” are worth mentioning. If you have an urban area right next to a body of water, like we do with the Chesapeake, you have the sun beating down creating very hot surfaces and upward transport that produces winds that circulate air between the water and the land. If you’ve been down to the beaches in the summer, you’ve probably noticed that there’s often a breeze coming off the water during the day. At night, it’s the opposite. Polluted air flows off the land and pools over the water.

Isn’t it good that polluted air pools up over the water rather than the city at night?
Not really because it comes back over land the next afternoon. There are actually Maryland Department of the Environment monitoring sites up at the top of the Bay that get higher concentrations than anywhere else in the state because of the bay breezes and the way the wind flow pinches at the top of the Bay. For example, the monitoring station at Edgewood, which is about 20 miles northeast of downtown Baltimore, tends to get hit particularly hard by bay breezes. DISCOVER-AQ is going to fly aircraft in that area, and the campaign should help us understand the full three-dimensional spatial picture over the Bay.

I’ve heard that the highest pollution levels can actually occur in the suburbs instead of directly over a city core. True?
That’s true for certain pollutants, like ozone. Ozone requires nitrogen dioxide, organic compounds, and sunlight to form. However, the process doesn’t happen immediately. It takes a few hours for the air to stew enough for ozone to form. When the wind is blowing through an urban area you can have your highest concentration of ozone downwind of a city by 20 to 30 miles.

Meaning rural landscapes don’t necessarily have pristine air?
No. In fact, farms in rural areas downwind of cities can have problems with ozone because ozone damages plant health as well as human health. Beans, for example, are highly sensitive. If ozone levels get too high, they start to get brown blotches on their leaves.

I know there are networks of ground-based sensors to measure ozone near the surface. Is it possible to measure ozone from space?
A spaceborne measurement of ozone at the ground would be a great thing, but it is still a real challenge. Much of the ozone we have on the planet is high in the atmosphere in a layer of air called the stratosphere. It’s about 15 miles up, and it’s hard to see through the stratosphere with satellite instruments because it is so thick. You could say getting a good ozone measurement is a holy grail right now for NASA and the air quality research community. We’re hoping that DISCOVER-AQ will get us closer.

Aircraft will also be flying over highways during the campaign. Why?
We know that transportation is a major source of pollution in the Baltimore area. I-95 is a big transportation corridor, and one of the things we want to look at with DISCOVER-AQ is the nitrogen dioxide released by combustion engines. There are very few nitrogen dioxide ground instruments in the area, so we’re flying over the highways to see if we can pick out a signal. We’ve been able to start measuring nitrogen dioxide from space in the last few years, but we can improve those measurements by validating them with ground data.

Credit information. Text by Adam Voiland. Flight tracks visualization by the Scientific Visualization Studio. NASA P-3B shot available here. Baltimore hazy/clear comparison from CamNet. Sea breeze illustrations from NOAA. Ozone-damaged leaf shot available here.

Smog Blog Outtakes

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On Earth Day, we published an interview about the “smog blog” created by Ray Hoff of the University of Maryland – Baltimore County. Today, we follow up by sharing this video, which has some striking shots of laser pulses from the instrument that Hoff’s atmospheric LIDAR group uses to take air quality measurements near Baltimore.


Plus, here are some outtakes from Hoff that did not fit into the original interview:

On the importance of satellites…
“We spend quite a bit of time trying to use satellite measurements as a surrogate for what we see on the ground because the Environmental Protection Agency can’t be everywhere. EPA has a thousand monitors in the United States, but those monitors are largely in urban areas, and they can be spaced quite far apart. There are, for example, no EPA samplers in Wyoming. NASA satellites can look everywhere.”

On why satellite measurements of aerosols are less accurate in the western U.S…
“In the West, the correlation between what happens on the ground is worse for two reasons. The land surface out in the western United States does not have as much vegetation, so it’s brighter and more difficult for NASA satellites to see the aerosols from space. The other thing is that there are a lot of fires in the West, which make it challenging to distinguish between aerosol types.”

On the challenges facing air quality researchers…
“One of the things they’d really like to have is better measurements of ozone at the ground level. Much of the ozone we have on the planet is in the stratosphere, about 20 kilometers or 15 miles up, and it’s hard to see through the ozone layer, since it’s so thick. We have to combine models with measurements from the ground and NASA airborne platforms, but the difficulty of seeing through this layer to surface ozone is kind of the holy grail of tropospheric air quality research right now.”

On geoengineering the climate with sulfate aerosols…
“A Nobel Prize winner has suggested putting more pollutants in the atmosphere in order to keep the planet cool. I actually think that’s a rather poor experiment for us to be trying with so little knowledge of how the atmosphere works. Humans have a pretty bad record of trying to “fix the planet.”

–Adam Voiland, NASA’s Earth Science News Team

Massive Air Pollution Event Highlights Sulfur Dioxide Trends in China

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This spectacular cloud of smog and haze formed over eastern China last week when a high-pressure weather system moved in to the area, allowing industrial and burning byproducts to settle with little disturbance from winds. As NASA’s Earth Observatory reported, NASA satellite instruments detected extremely high levels of sulfur dioxide, which most likely came from various industrial processes such as coal-burning power plants and smelters (facilities that melt or fuse ores in order to extract usable metals).

Satellites also detected high levels of aerosols — most likely sooty black carbon or organic carbon particles from wildfires and fossil fuel burning – that absorb sunlight and “trap” heat. In fact, the air was so thick with the light-absorbing particles at times that seeing the midday sun clearly would have been difficult. Bearing this out, news media reported numerous traffic accidents associated with the lack of visibility.

How does this event fit into broader pollution trends in the region? A study published earlier this year in Atmospheric Chemistry and Physics offers some insight. The authors, which included a researcher from Goddard Space Flight Center, analyzed sulfur dioxide emission trends in China since 2000 and made a number of notable observations. These included:

  • From 2000 to 2006, total sulfur dioxide emissions in China increased by 53 percent from 21.7 teragrams to 33.2 teragrams, an annual growth rate of 7.3 percent per year.

  • Geographically, emissions from northern China increased by 85 percent whereas emissions from the south increased by only 28 percent.

  • However, emissions started to decline in 2006, primarily due to the wide application of flue-gas desulfurization (FGD) devices in power plants.

Want more details? You can read the full paper here [PDF].

–Adam Voiland, NASA’s Earth Science News Team, Image courtesy of NASA’s Earth Observatory

Behind the Scenes With Scientists Who Created A Global Air Pollution Map

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Yesterday, NASA posted an article about a new global map of health-sapping PM2.5 air pollution. The Dalhousie University researchers who made the map used data from NASA’s MISR and MODIS satellite instruments, as well as information from a computer model called GEOS-Chem. You can read the news story here (or the accounts from Wired, Public Radio, and UPI), but we also wanted to share some of the audio from our interview with the scientists for those who want more details. The scientists being interviewed are Aaron van Donkelaar and Randall Martin; the person asking the question is Goddard-based science writer Adam Voiland.

What was the most interesting thing you found from this analysis?  

Why go to the trouble of making this map?

What’s the heavy band of particulate matter in Africa? Is dust bad for our health?

Martin: There’s no lower bound on health effects

Have other researchers done this kind of analysis?

Are these data ready for prime time?

How did you combine data from both satellite instruments?

–Adam Voiland, NASA’s Earth Science News Team

A Tale of Two Kenyas: Contradictions in Air Quality Stirred Researcher’s Pursuit of Atmospheric Science

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Charles Kironji Gatebe’s early years read like a cliché. He grew up barefoot and poor in the small Kenyan village of Kenda at the foot of Mount Kenya, the son of coffee sharecroppers who raised their family on pennies a day. He walked nearly 10 miles each way to school for nearly a decade. He lacked adequate texts and other school supplies.

What he didn’t lack on those long daily walks was clean air. It was the contrast between the clear skies of his boyhood home and the smog and fumes of the nation’s capital, Nairobi, that stirred within Gatebe a strong passion for science. In 1979, Gatebe (right) was selected to represent his elementary school at a national convention to celebrate the United Nations Educational, Scientific and Cultural Organization’s (UNESCO) International Year of the Child. He later won a physics prize in high school in 1984 from the Kenya Secondary Schools Science Congress. He enjoyed independent research so much that his physics teacher would allow him to conduct his own experiments in the lab alone at night or on weekends.

Gatebe’s passion, matched with natural aptitude, eventually led Gatebe to degrees from Kenya’s University of Nairobi and the University of the Witwatersrand in South Africa. Now a climatologist with a joint appointment at NASA’s Goddard Space Flight Center and the University of Maryland-Baltimore County, Gatebe has fashioned an award-winning career – including the rare honor of the World Meteorological Organization’s Young Scientist Award in 2000, and awards from the Kenyan government, German Academic Exchange Services, SysTem for Analysis, Research and Training (START), and the International Program in the Physical Sciences — for his innovative research on air pollution and its sources and effects on his country.

“Air quality in Kenya’s villages was and continues to be significantly different from the smog encountered in Nairobi. They vary so much that it seems you’re virtually in two distinct countries,” said Gatebe when asked to share what sparked his study of Kenya’s air pollution. During his graduate studies at the University of Nairobi, he devised a few climate projects that unexpectedly got the attention of the Kenyan government and United Nations Environment Program. One of those was a modeling experiment to measure vehicle pollution and predict pollution levels from the average speed and number of cars in use.

Gatebe also investigated the origins of the city’s air pollution; that is, how much Nairobi’s citizens and industry generated compared to what was transported in from other countries. “Charles’ Kenyan air quality research was quite breathtaking and significant,” said Michael King, a senior atmospheric scientist at the University of Colorado and former senior project scientist at NASA Goddard who recruited Gatebe to NASA in 1999. “It involved him regularly hiking to the top of Mount Kenya – which sits roughly on the equator — and collecting air samples of atmospheric aerosol particles that he analyzed for their composition to distinguish dust and other particles from local sources from pollutants arriving from as far away as southern Africa, India and the Sahara.”

The acclaim from the study came as a surprise, Gatebe says, but motivated him to stay the course. He knew he’d found his niche.

As a former child scientist, Gatebe is eager to inspire more kids to get involved in science. He’s dedicated himself to NASA’s Global Learning and Observations to Benefit the Environment (GLOBE) education program, and blogs about the science of current events for GLOBE’s Web site.

Gatebe’s latest work is based on what he calls an accidental discovery, not uncommon in science. In summer of 2008, he was part of a NASA field mission called Arctic Research of the Composition of the Troposphere from Aircraft and Satellites (ARCTAS). Arctic wind currents can carry a haze that affects local climate. Gatebe and colleagues flew aboard planes through smoke blown over the Pacific Ocean from land-based fires to evaluate the composition of the pollution that eventually forms Arctic haze. 

A ship passed beneath Gatebe’s plane, through his measurement field, triggering a mass of sea foam in its wake. When he later evaluated visible and near-infrared data from NASA’s Cloud Absorption Radiometer instrument that took the measurements from aboard the plane, he noticed a spike in brightness in the vicinity of the ship’s path. The bubbles in the wake increased light reflectance off the ocean.

The irony of the discovery was quite amazing to Gatebe. Ships were long thought to pollute the air and contribute to warmer climate through exhaust emissions. But they also appear to have a counterbalancing effect of cooling local ocean surfaces by as much as four percent. What he doesn’t know yet is just how much the cooling effect offsets the warming effect on the nearby environment. He hopes that others will further the work so the question doesn’t go unanswered.  

–Gretchen Cook-Anderson, NASA’s Earth Science News Team

Charles K. Gatebe (top, courtesy of C. Gatebe);  Zebras with hazy Nairobi in the distance (bottom, courtesy of Michael King).