Aerosol size distributions during haze episodes in winter in Jinan, China

Abstract Number concentrations and distributions of 10–10,000 nm particles in a large city (Jinan) in the North China Plain were measured in winter 2009. The mean number concentrations of nucleation mode (10–20 nm), Aitken mode (20–100 nm), and accumulation mode (100–1000 nm) particles, as well as total particles were 925, 6898, 2476, and 10,299 cm −3 , respectively. Two severe haze episodes, with elevated concentrations caused by pollutants accumulating, were observed. Accumulation mode particle concentrations were significantly higher during the episodes than on clear days, and nucleation mode particle concentrations were pronouncedly higher on clear days than during the episodes. The peaks of dominant number, surface area, and mass size distributions were around 30–50, 200–300, and 200–400 nm, respectively, both during the haze episodes and on clear days, but elevated mass and surface area concentrations around 500–600 nm were also observed during the haze episodes, suggesting these particles had significant contributions to haze formation. These particles were probably formed through larger droplets in cloud and fog evaporating. Two new particle formation events, probably triggered by strong photochemical processes on clear days and significant traffic emissions during haze episode 2, were found. Significant insights were made into haze formation in a polluted Chinese urban area.