Measurements of particle number size distributions and optical properties in urban Shanghai during 2010 World Expo: relation to air mass history

To investigate the air quality during 2010 World Expo, continuous measurements of particle number size distributions and optical parameters were performed at urban Shanghai from April to June 2010. Total particle number and volume concentrations in the size range 16–600 nm were 12 700±6200 cm⁻³ and 16±8 µm³/cm³, respectively. Meanwhile, the optical parameters, particle light-scattering coefficient b_sp,532nm and absorption coefficient b_ap,532nm were 210±140 Mm⁻¹ and 26±20 Mm⁻¹, respectively. Strong correlation (R=0.69) was observed between b_sp,532nm and the number concentration of accumulation mode particles, especially in the specific size range 300–500 nm (R=0.87). Cluster analysis on air mass history was performed to explore the relationship between air mass origins and the optical as well as microphysical parameters. Back trajectories were classified into four major clusters. Air masses came from the west direction, in which continental aerosols were predominant, associating with the polluted cases during the summertime in Shanghai. In addition, the northern air mass showed the lower values of aerosol single scattering albedo ω_0,532nm, indicating the presence of smaller light-absorbing particles originated from the North China Plain.