Published in Atmospheric Chemistry and Physics, an international study shows that the number of atmospheric aerosol particles measured at observation sites across Europe has, on average, declined since the beginning of the 2000s. The declining trend was also observed by the climate models studied, but on average the relative decrease was lower in the models than in the ground measurements. There are clear differences between different models in how they describe seasonal variation. The study utilized long-term time series data from 21 observation sites and results from five different climate models.