New type of soot particle discovered in India

A previously unrecognised form of soot particle, known as 'super-aggregates,' has been identified from wildfire emissions in India, US and Mexico.
Scientists led by Rajan Chakrabarty from Nevada's Desert Research Institute detected the soot particle in smoke plumes from wildfires in Northern California, New Mexico, Mexico City, and India.
For several decades, scientists have been trying to quantitatively assess the impacts of wildfire soot particles on climate change and human health.
However, due to the unpredictability of wildfire occurrences and the extreme difficulty in sampling smoke plumes in real-time, accurate knowledge of wildfire-emitted soot physical and optical properties has eluded the scientific community.

Unlike conventional sub-micrometre size soot particles emitted from vehicles and cook stoves, super-aggregates are on average ten times longer and have a more compact shape.
These particles have low effective densities which, according to the authors, gives them similar atmospheric long-range transportation and human lung-deposition characteristics to conventional soot particles.

"Our observations suggest that we cannot simply assume a universal form of soot to be emitted from all combustion sources. Large-scale combustion sources, such as wildfires, emit a different form of soot than say, a small-scale, controlled combustion source, such as vehicles," said Chakrabarty.
The multi-institutional research team first detected the ubiquitous presence of soot super-aggregates in smoke plumes from the 2012 Nagarhole National Forest fire in western India.

To verify the presence of super-aggregate particles in other fires around the world, the team next analysed smoke samples collected from the 2010 Millerton Lake fire in Northern California, and the 2011 Las Conchas fire in New Mexico, as well as wildfires near Mexico City.
The authors found that a large portion of soot emitted during the flaming phase of these fires were super-aggregates.
To assess the potential impact of super-aggregates on global climate, scientists also calculated the radiative properties of soot super-aggregates using numerically-exact electromagnetic theory.
"We found that super-aggregates contribute up to 90-per cent more warming than spherical sub-micrometre soot particles, which current climate models use," said Chakrabarty.

The research was published in the journal Nature Scientific Reports.