Even though we've learned a lot about how tiny particles in the air, called nanoparticles, grow in our atmosphere during the 21st century, it seems like the big models predicting climate change are not fully catching on to how these particles affect cloud formation and, as a result, mess with Earth's radiative balance. A team of researchers from the University of Helsinki, TU Wien, Stockholm University, and the Finnish Meteorological Institute got together and put this idea on the table in a review published in the Reviews of Modern Physics journal. They basically gathered up all the research done on these atmospheric nanoparticles, or aerosol particles, from the last 20 years.
The focus here was on those particles that are less than 25 nanometers in size – the really tiny ones. The researchers dug into how these particles grow and how that growth connects to predicting the formation of cloud droplets. They also explored how we could make better use of aerosol data in predicting climate.
So, here's the deal with these tiny particles – they do a double whammy on the climate. First, they mess with how much sunlight reaches the Earth's surface. Second, they play a big role in making clouds happen.
Clouds are like little droplet parties in the sky, and these droplets form when water condenses on the surface of aerosol particles in the air. Without these particles, clouds wouldn't be much of a thing unless the air was super saturated. The amount and type of aerosol particles decide how the cloud looks and how much sunlight it reflects back into space. If there are lots of aerosol particles, the cloud droplets are small, but there are more of them, making the clouds brighter and better at bouncing sunlight away.
Now, here's where things get tricky. Stuff like sulfur dioxide, ammonia, and certain chemicals humans throw into the air also create new particles. These particles grow big enough to mess with cloud formation and, in the end, the climate.
The growth of these tiny particles is picky and gets influenced by weather conditions, the gases and particles in the air. Usually, you see new particles forming on clear, sunny days. This is when vapor molecules team up and form clusters, providing a base for other vapors to condense on, creating particles big enough to join the cloud-making party.
In the review, the researchers wanted to be the bridge between the experiments done in labs and the big computer models. They aimed to cut down on the uncertainty linked with particle growth and give us a better shot at predicting climate changes.
One of the problems they pointed out is the uncertainty around how fast these particles grow, especially the really small ones under 5 nanometers. There's also a bit of a fog around the detailed description of how particles grow in the big climate models.
Runlong Cai, a postdoctoral researcher from the University of Helsinki, talks about how the latest experiments are cool and all, giving us a better understanding of how particles form and grow. But, throwing all that info into climate models is like putting too much stuff in your computer – it gets overwhelmed. Better models could help us figure out how human activities mess with the air and climate, painting a clearer picture of what's going on.
Juha Kangasluoma, a University Researcher from INAR, adds that the next big step is to figure out the role of different vapors in particle growth and to get better at modeling these vapors and growth in the climate models. It's like solving a puzzle to make our climate predictions more on point.