Aerosols have three different liquid phases

Aerosols – tiny droplets of liquid suspended in the air – have interesting chemical and physical properties.

They can be made naturally from sea spray and some biological processes, but they can be created from pollutants in coal power plants. They have a cooling effect on the atmosphere, so an increase in aerosols has complicated local climatic effects as well as lowering the quality of the air.

In 2012, a team of researchers from the University of British Columbia (UBC), Canada, and Harvard University in the US, found that aerosols could have two different liquid phases within the same particle.

Now, researchers from the same team at UBC have been able to show that, actually, three different liquid phases could form in one drop.

Liquid phases in aerosols separating as relative humidity decreases. Credit: Yuanzhou Huang

The team made particles that contained compounds with three different chemical properties: one with low polarity, one with medium polarity, and one made of ionic salty water. They used organic and inorganic material commonly found in pollution and natural aerosols to make these compounds.

They also added a dye to the particles that changed colour depending on polarity, called a solvatochromic dye. Using fluorescence microscopy, they were able to observe three different colours in their particles, showing that instead of mixing together, the aerosols had three distinct phases. These phases could be modified depending on surrounding conditions, like relative humidity.

The researchers could then examine the properties of the particles, seeing how they interacted with gases and how they cause cloud to form.

“We’ve shown that certain types of aerosol particles in the atmosphere, including ones that are likely abundant in cities, can often have three distinct liquid phases.” says Allan Bertram, a professor in the department of chemistry at UCB. “These properties play a role in air quality and climate. What we hope is that these results improve models used in air quality and climate change policies.”

The research is described in a paper published in PNAS.

Liquid phases in aerosols separating as relative humidity decreases. Credit: Yuanzhou Huang

More on aerosols:

• Aerosol atmosphere
• Aerosols have been around for a while
• Aerosol and greenhouse gas interactions determine frequency of extreme weather events
• Global warming levels masked by aerosols: study