The tagging method uses the same simulations, and there is also the same ozone change between the two simulations.
However, the additional tagging keeps track of the “chemical fate” of emissions from the different sectors. It allows a true attribution of parts of the ozone columns to different sectors.
Only with the tagging method,it is possible to show the individual partial columns in the right part of Fig. 3a.
When comparing the “zero road” case with the base case,the overall ozone change is small - the same 0.6 DU as reported by the perturbation method.
However, while the 3.5 DU partial ozone column tagged to road traffic vanishes in the “zero road” simulation,all the other partial columns, e.g. those tagged to industry or lightning, have increased by 2.5 DU (see also bottom part of Fig. 3).