‘Bottom-up’ inventories of carbon monoxide emissions, which estimate emissions depending on the activities thought to be producing them, are resulting in underestimates by as much as 380Tg per year in Asia (380 x10^12 grams), say a group of scientists in a paper published in the latest issue of Geophysical Research Letters.
An alternative is the approach adopted by the scientists in this latest research. ‘Top-down’ estimates allow emission levels to be calculated by using observations of resulting atmospheric concentrations.
Currently, the researchers do not understand why the discrepancy is occurring, Prasad Kasibhatla of the Nicholas School of the Environment and Earth Sciences at Duke University in the US and lead author of the report, told edie. There are two likely possibilities, he explained – either that the amount of fuel, particularly biofuel, is being underestimated, or that the mass of emissions per mass of fuel is being underestimated. Kasibhatla believes that in Asia biofuel use, such as wood and dung, is particularly hard to constrain.
The situation in Asia is likely to be being repeated around the world, say the researchers. They add that carbon monoxide emissions are also often closely related to emissions of other important trace gases and aerosols (see related story).
Nevertheless, Kasibhatla notes that there are uncertainties with both top-down and bottom-up estimates of emissions. However, as top-down emission estimates are so much higher something is being missed, he says.