Illustrative comparison of pollution-induced visibility reductions with (a) showing typical particulate matter concentrations (PM2.5) on a clean day and (b) on a polluted day in April 2011. For the Laki model simulation, daily mean particulate matter concentrations across Northern Europe during the first 3 months are of about the same magnitude as in (b). Note that the comparison is for illustrative purposes only because visibility reductions for the same change in particulate matter concentrations will depend on relative humidity and chemical composition of the aerosol particles. Credit: Ken Carslaw