Measurement and Evaluation of the Optical Properties of Diesel Particulate Emissions
Improvements in engine technology have led to drastic reductions in the mass emissions of particulate from diesel engines. Research is now focused on the characterisation of the particulate matter and its potential impacts as a climate forcing agent. Much is known about the role of greenhouse gases (GHG) in atmospheric chemistry, however atmospheric black carbon also makes an important contribution to the warming of the global atmosphere. This work investigates the optical properties of particulates which are shown to be affected by the proportion of black carbon linked to mixing state. Black carbon (BC) emitted from engines, and other combustion systems, is known to absorb solar radiation in the atmosphere and have a strong warming effect on climate, particularly on local scales. However, strong uncertainties arise because the per-mass light absorption is strongly influenced by other materials, such as semi-volatile organics, co-emitted with the BC (known as the �coating�). By studying emissions from a light-duty diesel engine rig using state-of-the-art, online single-particle instruments and comparing with equivalent ambient measurements, we have shown that this enhancement in light absorption only occurs once the amount of coating relative to the BC reaches a certain threshold, which isn�t normally the case for diesel emissions, except under cold start conditions.