As smoke from the large wildfires in Idaho and Wyoming spread out across America yesterday, two NASA aircraft flew up to investigate parts of that smoky plume.
The two planes, a DC-8, which is a converted passenger plane, and an ER-2, a purpose-built, high-altitude aircraft that can operate between 45,000 feet and 70,000 feet, are part of a multiweek NASA campaign to better understand how pollution affects climate.
The aircraft are currently based in Houston, and on Monday, researcher Robert Yokelson, an atmospheric chemist at the University of Montana, flew on the DC-8 as it sampled the smoke. Yokelson is trying to learn more about how smoke from wildfires affects the climate.
"What we have been doing is to try to fly along that smoke back towards Idaho and Wyoming and try to see how the smoke changes on a multiday scale," he said.
That's just part of the science being undertaken in a NASA mission called Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys -- abbreviated as SEAC4RS.
The mission includes the two NASA aircraft, a privately owned Learjet and hundreds of personnel.
A poorly understood interaction
As Yokelson explained, scientists are still working to understand how clouds and smoke interact. Whether the black carbon from wildfire smoke has a warming or cooling effect can depend on whether it is below the cloud, at the same level of the cloud or above the cloud.
With multiple aircraft, the researchers are able to fly underneath a cloud with smoke in it and above it at the same time. They can measure how the smoke changes as it goes through the cloud.
"Think of a cloud as a box with an in and out, and what's the difference between the in and the out -- that's something we don't know a lot about," said Yokelson.
The flights also allow NASA to compare what they measure while flying in the smoke with what Earth-observing satellites measure from far above them.
"It's a powerful validation opportunity," said Yokelson. "If we can show when the satellite sees X, what's really happening is X plus some little percent, then we can apply that to the global daily coverage that we have of the whole planet from fires."
In the Southeast, Harvard University researcher Daniel Jacob, an atmospheric chemist, is hoping to use the flights to better understand how aerosols affect that region's climate.
As many in the climate community know, the U.S. Southeast has not experienced the warming that much of the rest of the country has seen. Researchers have tried to understand the causes behind this "warming hole."
One explanation is that particulate pollution has reflected radiation and shielded the region from the effects of greenhouse gases. But pollution from emissions is not the only source of aerosols in the South.
Probing emissions of Southern forests
Trees, which are plentiful there, are a natural source of many organic aerosols. Researchers are not sure to what extent pollution affects these organic aerosols. They are trying to understand what might happen to the natural aerosols as the overall air gets cleaner.
"To what extent is pollution contributing to the presence of these [organic] aerosols? That seems to me to be a very important question," said Jacob.
Tomorrow, the NASA planes will fly over Mississippi, Alabama and western Georgia. While those areas are mostly forested with pine, which does not have as important an emissions contribution, Jacob suspects that the regional forests' understory of sweet gum trees might be a powerful contributor to organic aerosols.
"Sweet gum emits hydrocarbon like gangbusters," said Jacob.
As they return to Houston, the planes will collect data over the Ozarks, which have a very different type of forest, mostly oak, but which also emit a lot of organic aerosols, said Jacob.