It’s undeniable that our industrialized society has released large amounts of pollutants into the world, creating a dark cloud on the horizon. Combustion, in particular, produces large amounts of aerosols, including black carbon, which has a huge impact on climate change.
While this only accounts for a few percent of aerosol particles, black carbon is very problematic. This is because black carbon in clouds can absorb heat and inhibits its ability to reflect onto surfaces such as snow. Therefore, it is important to understand how black carbon interacts with sunlight. Researchers have quantified the refractive index of black carbon to the most accurate level to influence climate models.
There are many factors driving climate change. Some are very familiar, such as carbon dioxide emissions from burning fossil fuels, sulfur dioxide from cement manufacturing, or methane emissions from livestock farming.
Soot, or black carbon, is very good at absorbing heat from sunlight and storing it, adding to atmospheric heat. Also, given that dark colors are less effective at reflecting light and heat, as black carbon covers shallower surfaces, including snow, it reduces the chances of those surfaces reflecting heat into space.
In today’s atmosphere, black carbon is estimated to make the largest contribution to global shortwave aerosol absorption. Among all greenhouse gases and aerosols in the Arctic, black carbon is estimated to be the second largest contributor to positive effective radiative forcing.
Newly emitted black carbon particles (e.g. from industrial exhaust) can quickly undergo internal mixing with other major aerosol constituents.
The refractive index is the ratio of the speed of light in space to the speed of light in a medium. The new optical measurements of black carbon suggest that current climate models underestimate its contribution to atmospheric warming, and the team hopes other climate researchers and policymakers will benefit from their findings.
The method developed by the team to determine the complex refractive index can be applied to materials other than carbon black. It allows optical identification of unidentified particles in the atmosphere, oceans, or ice cores, and assessment of the optical properties of powders, not just those relevant to the ongoing problem of climate change.
The results of this new research have been described in the journal Aerosol Science and Technology recently. The paper was published under the title “Constraining the complex refractive index of black carbon particles using the complex forward-scattering amplitude” which is an open-access journal.