An advanced method of contributing emissions to short-lived chemical species (OH and HO₂): the TAGGING 1.1 submodel based on the Modular Earth Submodel System (MESSy 2.53)

To mitigate the human impact on climate change, it is essential to determine the contribution of emissions to the concentration of trace gases. In particular, the source attribution of short-lived species such as OH and HO₂ is important as they play a crucial role for atmospheric chemistry. This study presents an advanced version of a tagging method for OH and HO₂ (HO_<i>x</i>) which attributes HO_<i>x</i> concentrations to emissions. While the former version (V1.0) only considered 12 reactions in the troposphere, the new version (V1.1), presented here, takes 19 reactions in the troposphere into account. For the first time, the main chemical reactions for the HO_<i>x</i> chemistry in the stratosphere are also regarded (in total 27 reactions). To fully take into account the main HO₂ source by the reaction of H and O₂, the tagging of the H radical is introduced. In order to ensure the steady-state assumption, we introduce rest terms which balance the deviation of HO_<i>x</i> production and loss. This closes the budget between the sum of all contributions and the total concentration. The contributions to OH and HO₂ obtained by the advanced tagging method V1.1 deviate from V1.0 in certain source categories. For OH, major changes are found in the categories biomass burning, biogenic emissions and methane decomposition. For HO₂, the contributions differ strongly in the categories biogenic emissions and methane decomposition. As HO_<i>x</i> reacts with ozone (O₃), carbon monoxide (CO), reactive nitrogen compounds (NO_<i>y</i>), non-methane hydrocarbons (NMHCs) and peroxyacyl nitrates (PAN), the contributions to these species are also modified by the advanced HO_<i>x</i> tagging method V1.1. The contributions to NO_<i>y</i>, NMHC and PAN show only little change, whereas O₃ from biogenic emissions and methane decomposition increases in the tropical troposphere. Variations for CO from biogenic emissions and biomass burning are only found in the Southern Hemisphere