Many European countries share radiological monitoring data with each other, and this is made available to the public through the Joint Research Council: https://remon.jrc.ec.europa.eu/
I'm not sure if it's possible to get historical data, but if so it could be interesting to have a look at data from January.
There are also communities of hobbyists that track radioactivity with custom or home-brew stations. While less sophisticated in what they measure they can be an another point of reference. One of the oldest around is http://radioactiveathome.org/map/ another is http://www.uradmonitor.com/
I'm not sure if it's possible to get historical data, but if so it could be interesting to have a look at data from January.