In order to understand how the Industrial Revolution affected the air we breathe, environmental engineers need to find pristine air particles. To do that, they have to go 40m above the remotest corners of the Amazon rainforest.
Finding air that is still in an essentially pre-industrial state is a surprisingly difficult task, but without such particles to act as a baseline it's difficult to know precisely how the last two centuries have changed our atmosphere. Although there are still a number of tiny pockets around the world unaffected by industrial activity, the trick is finding somewhere that is isolated from pollution and contamination for thousands of miles.
Researchers found just the place high above the remote Amazon Basin of Manaus, Brazil, as team leader Scot Martin explains:
"We basically had two 'travel' days worth of pure air movement over 1,600 kilometers before the air came to our measurement site. By performing the study in the rainy season of central Amazonia (January-March), we avoided contamination. Well-known periods of burning and deforestation occur in the dry season and also largely on the southern edge of Amazonia."
Their data represents the first time ever we've captured pristine aerosol particles, and this new information will help us better understand the difference between natural and industrial environments, the subtleties of cloud formation, and how the deforestation - and resulting atmospheric changes - could affect the world as a whole.
Intriguingly, the particles may be set to overturn some basic assumptions about how atmospheres are put together. Much to the researchers' surprise, droplets created from the oxidation of plants comprised a massive 85 per cent of all the particles in the system, which is completely different from industrialised atmospheric conditions, not to mention what we find in natural marine environments. This could mean the natural interactions between aerosols and these droplets, known as secondary organic particles, is totally different from what scientists previously thought, because we had based all our assumptions on essentially industrial environments.
They also found that there were only a few hundred total particles per cubic centimtre, compared to over 10,000 such particles per cubic centimetre in heavily industrialised cities. All the "noise" created by soot and other pollutants makes it all but impossible to track changes to atmospheric conditions when new particles are added, but that won't be the case when there are so few particles in the clean air to begin with.
Co-author Urich Pöschl says these findings will be crucial to understanding how humans have altered the atmosphere in the last 200 years:
"The new insights and data help us and our colleagues to understand and quantify the interdependence of the cycling of aerosols and water in the unperturbed climate system. A thorough understanding of the unperturbed climate system is a prerequisite for reliable modelling and predictions of anthropogenic perturbations and their effects on global change."