Hi @sineadn, sounds like you’re well across what you’re doing, but I ask a primitive question - where did you get material properties from? Solar and visaul absorbtance in particular. It loooks a bit high at the first glance.
We did a study comparing reflectance parameters and it’s very critical for MRT results, more than surface temperature outcomes. May check out the discussion here MRT with UTCI (HB)_Materials impact - grasshopper / honeybee - Ladybug Tools | Forum
Is the grid set up at the same height with the site measurements?
As an idea, could cloud cover create the spike in the air temp observations?