AbstractIn January 2013 exceptionally high levels of particulate matter (PM) concentrations were reported for the area around Beijing (40 N, 116 E) with maximum concentrations exceeding 500 μg/m3. Observations of the aerosol optical depth (AOD) within the Aeronet sun-photometer network showed an AOD of more than 2 on several days. In order to analyze this high pollution episode PM concentrations in China were simulated with the Community Multiscale Air Quality (CMAQ) model for the period from 10 December 2012 to 31 January 2013. Emissions were taken from the EDGAR data base. The most recent emission rates from 2008 were further increased considering the growth of China’s gross domestic product. The results were compared to ground based PM2.5 measurements taken at the US embassy in Beijing and to Aeronet sun-photometer observations. The model was generally able to reproduce the high PM levels measured in situ close to ground, however the largest peak on 12 January was not captured, because of an exceptionally strong temperature inversion close to ground that was not reproduced in the meteorological fields. The meteorological model significantly underestimated the relative humidity in the lowest layer, leading to some underestimations of the aerosol optical depth. An analysis of the most important source sectors showed that residential heating was the main emission source sector on those days with the highest aerosol concentrations.