Evolution of the mixing state of fine aerosols during haze events in Shanghai

The composition and size of individual atmospheric particles were measured by aerosol time-of-flight mass spectrometry (ATOFMS) in Shanghai for the period December 14–23, 2008. Carbonaceous particles were the dominant aerosol type in terms of number fraction during the entire period. Noticeably, the mixing state of carbonaceous particles showed dramatic changes from fresh elemental carbon or biomass burning particles to aged ones with the addition of secondary components, mostly ammonium nitrate and secondary organic compounds, during heavy haze events. Our real-time single particle data suggest that change in the mixing state played an important role in increasing light extinction of aerosols during haze events in Shanghai.