Black-carbon absorption enhancement in the atmosphere determined by particle mixing state
Authors: Dantong Liu, James Whitehead, Rami Alfarra, Ernesto Reyes-Villegas, Dominick Spracklen, Carly Reddington, Shaofei Kong, Paul WIlliams, Jonathan Taylor, Michael Flynn, William Morgan, Gordon McFiggans, Hugh Coe, James Allan
Journal: Nature Geoscience
Publication Date: 27 February, 2017
Department of: Earth and Environmental Sciences
Unlocking the key to the ‘blackness’ of atmospheric soot
Researchers at the University of Manchester have determined a key factor controlling the climate-impacting properties of black carbon (BC). BC in anthropogenic soot is known to have a very strong influence on climate and weather, particularly on regional scales, but there is a major source of uncertainty due to the so-called ”lensing” effect, whereby material co-emitted with the BC or added during atmospheric processing coats the BC and increases its darkness by 50% or more. While lensing has been demonstrated during laboratory tests using model soots, evidence for it being a factor in the atmosphere has so far been inconsistent.
This work analysed ”real world” soots in the form of emissions from an automotive diesel engine in the laboratory and atmospheric soot in Manchester, specifically emissions from traffic, wood burning and bonfires on Guy Fawkes night. By using a combination of specialist online instruments measuring the mass and optical properties of individual particles, it was shown that the mass ratio of coating to BC must reach a threshold of around 1.5 for lensing to occur, likely to be because thinner coatings fail to fully envelop the BC. This new understanding will improve the accuracy of climate model predictions.
- In this work, the ‘lensing’ effect of black carbon optical absorption enhancement has been linked to source and mass fraction
- A new hybrid model of atmospheric black carbon optical properties is proposed whereby a threshold of coating is required before absorption enhancement occurs