LAUSR

ABSTRACT A single particle soot photometer (SP2) and a single particle aerosol mass spectrometer (SPAMS) were deployed to investigate size distribution and mixing state of ambient black carbon (BC) particles in Shanghai in the winter of 2017.  Noticeably, the mixing state of BC particles changed drastically under different meteorological conditions. Higher BC concentrations were often observed during “haze episodes”. BC particles were found to have two size modes: the “condensation mode” and “droplet mode”. The condensation mode mainly consisted of fresh traffic emission particles. The droplet mode included three types: highly aged traffic emission particles, biomass burning particles and heavy duty diesel engine emission particles. The highly aged traffic emissions had a smaller core size (60 to 80 nm) and very thick coating (100 to 160 nm in thickness). Biomass burning particles had a slightly larger BC core size (80 to 130 nm) with a much thicker coating (160 to 300 nm) compared to traffic emission. We observed a large number of BC particles with large core size (150 to 200 nm) and relatively thin coating thickness (40 to 80 nm) in clean days. Based on air mass trajectory analyses, the air mass during haze episodes were mostly from local areas and long range transport from the North China Plain, while the air mass during clean episodes were mostly transported from the East China Sea. Interestingly, BC particles in this clean air mass contained more V-containing particles and exhibit strong signals for Ca+ in mass spectra. This type of BC particles may come from the heavy machinery emission near ports. Our real time single particle data suggested that source identification of BC aerosols can be readily obtained based on the measured BC particles size distribution and their mixing state.