For the most recent years (2000-2021) we use a dataset that combines ground-level and satellite observations of PM2.5 concentrations (from Van Donkelaar et at (2021)), satellite dataset can be found here (V5 0.1 degree resolution). Satellite observations of PM2.5 aren’t available for the years before 1998, so instead we take the historical trend in air pollution from computer models (Turnock 2020); publicly available model data was taken from the Coupled Model Intercomparison Project (CMIP6), these are the climate models used for the IPCC assessment report. We used data from the UKESM submission to CMIP (data is here).
To ensure a smooth time series, we don’t use the model concentrations directly, instead we use them to calculate the historical trend for each city and apply this trend to a three-year average of the observations from 2000-2002. This is a similar approach to that taken by Turnock et al. (2023) and Reddington et al. (2023).
Because so few historical observations of PM2.5 exist, so it is challenging to evaluate how good this approximation is, but in our approach the historical trend is taken from the computer model and the values are informed by the satellite.
-The historical concentrations for the UKESM model are calculated using the emissions inventory developed through the Community Emissions Data System (CEDS) developed by Hoesly et al, 2018 +
The historical concentrations for the UKESM model are calculated using the emissions inventory developed through the Community Emissions Data System (CEDS) by Hoesly et al, 2018
These images will be updated in the future as improved model simulations and observations become available.
Both the computer model and the satellite use gridboxes that cover many kilometres, so concentrations from cities will likely be underestimated as the very concentrations in a city center may be mixed with lower concenrations within the same gridbox.