Environmental engineers working in a remote part of the Amazon Basin near Manaus, Brazil, have isolated particles from the atmosphere in “near pristine pre-industrial conditions,” according to a paper published in the September 17th issue of Science.
The particles were captured from air flowing over a 40-meter-high tower during the rainy season, when the burning from deforestation has temporarily stopped, and are free of the soot, nitrates and other junk found in particles captured from the air above industrialized cities.
They should give us clues to what life was like on Earth before we humans became so widespread. They’re described by the engineers as “liquid organic particles” – particles that were released by plants in their normal course of growing and interacted with other molecules in the air.
From the National Science Foundation, which funded the research:
In the atmosphere, gas-phase molecules emitted by plants are attacked by very specific molecules such as ozone or hydroxyl radicals that then change the chemical structure of the organic emissions by adding oxygen atoms.
As a result, the gas-phase molecules become far less volatile and condense to form new particles or, alternatively, to grow pre-existing particles. These particles serve as the nuclei on which atmospheric water condenses as climate-important clouds form.
This cloud-forming activity caused by particles is well known to scientists, who also know that clouds influence the climate and can harm human health if they’re polluted. (Remember acid rain?)
What’s not known is how many particles are pristine as opposed to polluted and whether/how polluted particles behave differently in clouds.
One difference is in their numbers -- there are many fewer pristine particles over the Amazon than there are polluted particles over cities, the engineers discovered: The concentration of pristine particles above the Amazon Basin was several hundred per cubic centimeter, compared to tens of thousands of polluted particles per cubic centimeter over cities.
(Here’s another paper from the same issue of Science that describes how carbon monoxide caused by combustion can affect the number of particles, their mass and how they scatter light).
For the first time, though, scientists now have a way to compare what the atmosphere was like before industrialization to what it's like now and keep monitoring it for changes.
How will the deforestation that’s been going on in Brazil affect cloud formation? Or climate change? Time will tell.
(The picture, by Delphine Farmer, is of the sunset over the Rio Solimoes in the Amazon).