Nano-scale clusters shed light on the fate of aerosols
When it comes to aerosols and their impact on the environment, the first thing that comes to mind is often the ban on ozone-depleting chemicals (CFCs) in the 70s. Whilst these chemicals are long gone, other aerosols are still used and released in the atmosphere worldwide, and the truth is there is still much we don’t know about their impact on the environment. As Dr Katrianne Lehtipalo, from the University of Helsinki’s Institute for Atmospheric and Earth System Research, explains, “there is a large variability in both the sources (natural and anthropogenic) and properties (concentration, size, composition etc.) of aerosol particles, which makes it difficult to accurately model their impacts on clouds and climate. We need to know more about how aerosols are formed and how they transform in the atmosphere.” This was the mission at the heart of the nanoCAVa (Formation of nano-scale clusters from atmospheric vapors) project. Over three years and with help from research groups at the University of Helsinki and the Paul Scherrer Institute, Dr Lehtipalo aimed to advance current understanding of the fine line between the gas and condensed phases of aerosols, by studying the formation of nanoscale clusters from atmospheric vapours. “Our approach consisted in combining detailed laboratory studies, investigating the basic properties and formation mechanisms of aerosol particles in long-term field studies. This is a powerful combination, which allows us to use our expertise gained from years of atmospheric studies to plan lab experiments relevant to the atmosphere and current research questions. On the other hand, this allows us to test whether the mechanisms found in the lab and related models can explain real atmospheric observations,” Dr Lehtipalo says. Thanks to recent breakthroughs in instrumentation able to detect atmospheric vapours, clusters and recently formed aerosol particles, the project team could measure clusters in the atmosphere and study their formation process in the CLOUD chamber at CERN. Not even the aerosols with the lowest atmospheric concentrations could escape these detection methods. The team now have a better understanding of the concentrations and composition of sub-3 nm clusters in the atmosphere; and they could even find new formation and growth mechanisms of aerosol particles – notably sulfuric acid, ammonia, amines and organic vapours. “Our results are among the first indicating how clusters and nano-particles are formed almost everywhere in the atmosphere, from clean countryside to urban megacities. Their sources and concentrations are of course varying a lot, and we hope to get more insight on that in the future, as well as to understand better what controls the growth of the clusters to climate-relevant sizes,” Dr Lehtipalo explains. Although the project has now come to an end, the team intend to continue their work. New field measurements are currently ongoing in different parts of the world, and additional lab experiments are waiting to be analysed. Dr Lehtipalo also points at the need for more robust and reliable instrumentation for long-term atmospheric measurements as, she admits, there are still many parts of the atmosphere we have yet to understand.
Keywords
nanoCAVa, aerosols, nano-scale clusters, particles, environment
