The air above the Amazon rainforest is cleaner than almost anywhere else on earth, thus allowing the team to measure particles emitted or formed within the rainforest ecosystem that are relatively free from the influence of anthropogenic or human activity. The environmental engineers or 'archeologists of the air' hope the study will further their understanding of cloud formation, which affects levels of precipitation and the ability to grow crops and plants, as well as climate change.
'We basically had two "travel" days worth of pure air movement over 1 600 kilometers before the air came to our measurement site,' said lead author Scot Martin, Gordon McKay Professor of Environmental Chemistry at the Harvard School of Engineering and Applied Sciences (SEAS) in the US.
Professor Martin explained that by 'sampling from a 40-metre high tower and using a range of techniques, the researchers detected and imaged atmospheric particles' and found that 'particles in the submicron size regime most relevant to climate could be traced to the atmospheric oxidation of plant emissions, or so-called secondary organic aerosol droplets'.
He described this as 'a kind of liquid organic particle' and said it was the first time that anyone has ever imaged one of these particles in isolation 'because in the northern Hemisphere and other anthropogenic regions, when you collect a particle it is a mess and filled with soot, nitrates, and other pollutants'.
In the pristine Amazon Basin the researchers were able to detect aerosol particle number concentrations of a mere several hundred per cubic metre (cm3) - in heavily industrialised cities, particles concentrations are in the tens of thousands per cm3, making it impossible for climate scientists to measure any net change when additional particles, either natural or artificial, are added.
However, it is essential that scientists manage to measure such changes, as Professor Martin highlighted. 'Those particles are affecting cloud formation and cloud formation is affecting precipitation which is affecting the plants,' he said 'This is what we call the great tropical reactor. Everything is connected and in our research we finally had a real glimpse of natural aerosol-cloud interactions'.
Lead co-author Ulrich Pöschl, a scientist at the Max Plank Institute for Chemistry in Germany, said: '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'. He added that 'a thorough understanding of the unperturbed climate system is a prerequisite for reliable modeling and predictions of anthropogenic perturbations and their effects on global change'.
As the Amazon Basin is going through a period of development, co-author Paulo Artaxo, a professor of physics at the University of São Paulo in Brazil, highlighted that scientists will now have an opportunity to watch the influence of human activity on the atmosphere in real time. 'In Brazil, we now have even more solid science to support sustainable development in the Amazonian region,' he noted.
'Looking ahead, we hope to clarify the mechanisms of how vegetation interacts with the atmosphere and elucidate the main natural feedbacks. Doing so will give us a way to monitor atmospheric change accurately in light of ongoing deforestation.'
Source: Cordis news release
Citation: Pöschl, U., et al. (2010) Rainforest aerosols as biogenic nuclei of clouds and precipitation in the Amazon. Science, published online 17 September. DOI: 10.1126/science.1191056.
For more information, please visit:
Harvard School of Engineering and Applied Sciences (SEAS): http://seas.harvard.edu/
Max Plank Institute for Chemistry: http://www.mpch-mainz.mpg.de/mpg/english/index.html