# UKCA Chemistry and Aerosol Tutorials: Background Motivation

These UKCA tutorials are designed with the following premise:

What are the most common things that a PhD student or Researcher will need to know how to do when they start using UKCA?

Often you will want to use UKCA to answer questions like these:

• What happens when I add in reaction A to form new species B?
• What is the effect of changing the emissions of C?
• How does the deposition of D affect process E?
• How do my changes affect the aerosol properties?
• What is the budget of F?
• Output the fluxes of reactions G, H, and I to diagnose it.

When you have completed the UKCA Tutorials you should have a basic understanding how to make the required changes needed to answer these questions.

Throughout the tutorial you are asked to perform a series of tasks. In fact, these are mostly part of one big task which is:

Create two new species, ALICE and BOB, then include emissions of ALICE and the reaction
${\displaystyle {\textrm {ALICE}}+{\textrm {OH}}\longrightarrow {\textrm {BOB}}+{\textrm {Sec}}\_{\textrm {Org}}}$
before including the dry deposition of ALICE and the wet deposition of BOB. You should also output the fluxes through the reaction and deposition processes. You will then look at several aerosol diagnostics and perform a sensitivity experiment.

Despite seeming to be straight-forward, this is actually quite a big task as it involves

• Rose changes
• Editing of STASHmaster_A (diagnostic definition) file & associated metadata changes
• Changes to STASH (diagnostic) output
• UKCA code changes
• New species
• New emissions
• New/editing reactions & deposition
• Working with various UM files
• Regridding input data
• Creating NetCDF files
• Processing UM output

When working with UKCA it is important to

1. Break the tasks down into manageable chunks (this is why the task is split across several tutorials)
2. Remember that UKCA currently sits within the UM framework

The Tutorials are broken down into three sections

1. General use of UKCA and Rose (Tutorials 1-3)
• These three tutorials cover the basics of the copying and running a UKCA suite, before outputting a field through STASH
2. UKCA Chemistry (Tutorials 4-9)
• These tutorials break down the chemistry task into 6 smaller chunks