Indoor PM2.5 and its chemical composition during a heavy haze–fog episode at Jinan, China

PM2.5 samples were collected in both a typical laboratory (indoors) and adjacent courtyard (outdoors) in Jinan, China from 12 January to 4 February 2013. The samples were analysed for 10 inorganic water-soluble ions, 14 elements and carbonaceous species to investigate their chemical characteristics and relationships with indoor and outdoor PM2.5 during a severe haze–fog (HF) episode and a normal (NHF) period. The average indoor and outdoor PM2.5 concentrations during the HF episode were 236 μg/m3 and 409 μg/m3, respectively, whereas the corresponding figures for the NHF period were 62 μg/m3 and 87 μg/m3. The predominant component was (NH4)2SO4, which accounted for 55.07% and 44.43% of the total measured species of indoor and outdoor PM2.5, respectively, in the HF episode, and 40.31% and 32.93%, respectively, in the NHF period. The indoor NH4NO3 level was significantly lower than the outdoor level due to volatility. The indoor and outdoor concentration ratios, infiltration rates, and indoor-generated concentration of PM2.5 and chemical compounds (SO42−, NO3− and EC) indicate that the aforementioned species had primarily outdoor sources, whereas NH4+ and OC and all the measured elements appear to have indoor sources, Cu in particular.