Air Monitoring: How Does Black Carbon Affect the Climate?

Black carbon, more commonly known as soot, is capable of absorbing heat from the sun’s rays in the atmosphere. In this way, it contributes to global warming in much the same manner as other greenhouse gases (GhGs), although its full impact is not yet fully understood.

In an attempt to shine a light on this under-investigated area of research, a team of scientists from the Michigan Technological University have published a study which reconciles empirical observations with the results of model simulations.

Their research has revealed that not only are black carbon particles comprised of different shapes, but that they interact with both organic and inorganic matter in a variety of ways. These interactions have a knock-on effect on the heat absorption properties of the black carbon particles.

Squaring the circle

For many years, the scientific community had imagined black carbon as being composed of spherical particles, which interacted with and became coated by other matter as its travelled through the atmosphere. It was assumed that these other particles had a lensing effect on the carbon, focusing the sun’s rays on the soot and enhancing its absorption capabilities.

However, sophisticated new methods of monitoring black carbon have allowed us to understand more about this contaminant than ever before. Seizing upon this capability, associate atmospheric scientist at Brookhaven National Laboratory Lauren Fierce decided to combine it with a new particle-resolved model to gain greater insight into the behaviour of black carbon.

“Whereas most aerosol models simplify the representation of particle composition, the particle-resolved model tracks the composition of individual particles as they evolve in the atmosphere,” explains Fierce. “This model is uniquely suited to evaluate errors resulting from common approximations applied in global-scale aerosol models.”

Less potent than previously believed

Whereas previous models had assumed that all black carbon particles would constitute the same spherical shape and attract uniform amounts of organic and inorganic matter, Fierce’s experiment acknowledged the inconsistency of black carbon in the real world. This allowed her to reconcile the empirical data with the statistical models, resulting in the realisation that black carbon does not have as strong a warming effect on the atmosphere as previously thought.

Fierce’s research has not reached a definitive conclusion over the impact of black carbon, but it does provide a valuable framework by which future studies can develop our understanding of how the substance behaves in the atmosphere.

Moreover, black carbon persists in the atmosphere for a mere matter of weeks; by contrast, carbon dioxide can endure atmospherically for hundreds of years. Therefore, while black carbon can pose a problem for global warming and limiting its emissions is a step in the right direction, the achievement of other GhG emissions reductions targets (such as CO2 and methane) are more pressing concerns.