Aerosol problem: Adding a piece to the climate change puzzle
HOUGHTON –Researchers at Michigan Technological University have discovered particles from wildfires may be staying in the atmosphere longer than previously thought, adding new considerations to climate prediction.
When it comes to climate change and modeling, “it’s complicated”‘ is not the desired answer but it is the situation scientists find themselves looking at. While topics like greenhouse gasses and their relation to warming rates are fairly well understood, there’s a lot more to the atmosphere.
For Tech researchers Claudio Mazzoleni, Lynn Mazzoleni and Simeon Schum, the focus is on organic aerosols, one of the factors that still is not well understood.
Aerosols are small particles that are suspended in the atmosphere which can be from a range of sources including a backyard barbecue, factories or for this research, wildfires.
To study these particles they headed to Pico Mountain in the Azores archipelago. The mountain has the unique quality of being able to access the boundary layer and the free-tropospheric layer. Since particles travel through these layers, Pico was perfect for collecting samples and they walked away with three good ones.
They found two of the samples were from a wildfire, likely in Canada and transported through the free-troposphere. The remaining aerosol, was from a normal emission and had been transported through the boundary layer.
The issue was the two samples from the free troposphere was less oxidized, or combined with oxygen, then they would have thought for the length of time it had been in the atmosphere. These were the particles that originated in wildfires in Canada and traveled to Pico.
“Generally as you leave stuff in the atmosphere it gets more and more oxidized. The longer it’s in the atmosphere the more it gets oxidized, that’s the general gist of how it should work,” said Chemistry graduate student Simeon Schum. “However, what we saw was the ones that had been in the atmosphere longer were less oxidized than the one that had been in the atmosphere for less amount of time.”
The samples were oxidized at the rate previously expected for a few hours or days but had been in the atmosphere for a week.
The question was why.
Researcher and associate professor of chemistry, Lynn Mazzoleni’s theory is that it depends on the state of the natural aerosol, either a solid, liquid or in between. The more solid a particle the harder it is for it to oxidize.
“It turns out that probably the amount of water that’s associated with the aerosol particles plays a really strong role because water turns out to be a pretty strong plasticizer,” she explained.
They suspect this is due to the temperature and humidity, with cooler temperatures keeping the aerosols in a marble-like state. Additionally, with wildfires, the fire column may get high enough to push the aerosols into the free troposphere where there are fewer oxidants.
“If the oxidants can’t get into the particles then the particles can’t age very much which is what we think happens,” Mazzoleni said, describing the process as similar to adding milk to mashed potatoes, a task that’s much more difficult if the potatoes are frozen.
The tricky part is aerosols come from different locations and have very different rates of oxidation based on their chemical composition so that rate of oxidation is hard to quantify.
So why is this important?
Aerosols and clouds are factors that help scatter solar radiation coming in and potentially lessen greenhouse effect.
However, the impact of aerosols on the atmosphere is not very well understood and natural aerosols come from a range of sources. What researchers do know is these particles impact light in different ways depending on their color, something the sun can bleach to become non-absorbing which is tied to oxidation. Black aerosols absorb radiation, contributing to a warming effect while brown aerosols from wildfires can either absorb light or reflect it depending on the darkness, said associate physics professor Claudio Mazzoleni.
If the oxidation rate is slower and the brown aerosols are sticking around longer than suspected they may be absorbing light rather than being more reflective, contributing to warming and adding a new consideration to climate modeling.
“If (we) have this amount of CO2 and warming and aerosol absorbs more than were thinking temperature could be higher in the future that we were expecting with this amount of CO2,” He explained.
Their information could help figure out a more accurate picture of what to expect.
“All scientists are trying to figure out as much as we can about our earth’s system in terms of especially trying to really get a good estimate for what extent of warming we could expect to have in 10-20 years,” Lynn Mazzoleni said.