A theoretical comparison between intentional elemental and isotopic atmospheric tracers

Abstract

Abstract A theoretical comparison has been made between intentional elemental and intentional isotopic tracers for the study of the fate of emissions into the atmosphere. The use of an elemental tracer requires a very large signal to background ratio because the latter cannot be determined while the tracer experiment is in progress. It is shown that the variation in the ambient background is the major source of uncertainty for the elemental tracer. The use of a stable isotopic tracer is definitive because the isotopic composition of the background is constant and can be measured in real time during the isotopic analysis of the sample. Simple error analysis suggests that the isotopic tracer is intrinsically definitive and more accurate compared to the elemental tracer. This is because elemental tracers are subject to inherent biases of unknown magnitude that do not exist for isotopic tracers. If it is assumed that the background can vary by a factor of two during a tracer experiment, then for a given confidence in the detection of the tracer signal more than 10 4 times more elemental tracer is required than isotopic tracer. It is concluded that stable isotopic tracers are inherently superior to elemental tracers; however; this conclusion now needs to be demonstrated in an actual field experiment.