This study shows the influence of two large wildfires (one of which was the largest wildfire ever recorded in the region of Castilla y Leon) in the north-west of the Iberian Peninsula upon the atmospheric air quality of the city of Leon, Spain, at approximately 70 km from the fires, on days with a strong subsidence inversion associated with high pressures. The vertical dispersion of the smoke plume was inhibited and this caused an increase in the particulate matter (PM) in the atmosphere. During this event, average values of up to 1700 +/- 600 particles cm(-3) were registered, most of which corresponding to the smallest fraction of the fine mode. On the other hand, the count median diameter of the fine mode (CMDf) increased gradually from 0.09 to 0.14 mu m. The PM10 and PM2.5 reached hourly values of 89 and 36 mu g m(-3), respectively. This study also estimates the changes in the optical properties of the particles as well as the associated radiative forcing. The presence of an important load of absorbing aerosols was detected, with instantaneous radiative atmospheric forcing up to + 134.6 Wm(-2). The estimations of the respirable fractions showed in healthy adults high levels of mass concentration of the aerosol that reaches the bronchioles and alveoli (up to 43 mu g m(-3)). (c) 2017 Elsevier B.V. All rights reserved.