Newswise – MUNICH – Looking inside common air particles provides important clues about their effects on climate and health, according to a new study by chemists at the University of British Columbia.
Secondary organic aerosol (SOA) particles are ubiquitous in the atmosphere and play an important role in air quality and climate. They can contribute to air pollution and damage the lungs, as well as help deflect solar radiation or promote cloud formation.
Different types of SOAs can mix together in a single particle, and their environmental impacts are governed by the physical and chemical properties of the new particles, in particular the number of phases – or states – in which they can exist.
In a new research letter published in the European Union Open Access Journal of Geosciences Chemistry and physics of the atmosphere, an international team of researchers found that two-phase particles can form when different types of SOAs mix together. The finding could help improve current models that predict the effects of OSA on climate and health.
“Until now, models have often assumed that when SOA types mix together in the same particle, they only have one phase. But we found that this is not always the case, which means that current models may not capture some of these effects correctly,” says lead author Fabian Mahrt, postdoctoral fellow at the Paul Scherrer Institute and the UBC Chemistry Department. The work was funded by the European Union’s Horizon 2020 research and innovation programme.
The team found that six of 15 mixtures of two types of SOA commonly found in the atmosphere produced two-phase particles. Importantly, they also found that the number of phases depends on the difference in the average oxygen-carbon ratio between given SOA types. It’s a fairly simple but potentially powerful way to represent such effects in models. When this difference is 0.47 or more, the researchers found that the particles would have two phases.
“We can now work with very complex organic molecules, calculate a single parameter that gives us information about the properties of a particular SOA mixture, and then potentially map fairly large-scale impacts,” says Allan Bertram, a scientist specializing in aerosols and main author. UBC’s Department of Chemistry.
This type of SOA mixing can occur especially when plumes of SOA particles, which have been in the atmosphere for some time, blow from rural environments over cities where newly produced SOA particles are emitted, says Mahrt. .
“If we assume that this mixture of plumes forms particles with a single phase, we might overestimate the total mass of organic particles in these areas, and therefore the health effects for these people.” The team of scientists hope the discovery can help improve models and ultimately ensure policies and regulations are based on sound scientific understanding.
Building on previous work, the researchers used fluorescence microscopy to look inside mixed SOA particles in their current experiments, injecting them with a dye that causes the phases of the particles to emit different colored light depending on of their polarity. The researchers then used these colors to directly infer the phase number of the mixtures, providing direct visual evidence of multiple phases.
“The study is evidence that we need to look at this phenomenon more carefully to get the full picture. We still have one piece of the puzzle, but we haven’t necessarily completed the puzzle yet,” says Mahrt. The research team hopes that other scientists will now experimentally expand the number of SOA mixtures and include the results in atmospheric models in the future.
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