Measurement of aerosol number size distributions in the Yangtze River delta in China: Formation and growth of particles under polluted conditions

Particle size distribution is important for understanding the sources and effects of atmospheric aerosols. In this paper we present particle number size distributions (10 nm-10 μm) measured at a suburban site in the fast developing Yangtze River Delta (YRD) region (near Shanghai) in summer 2005. The average number concentrations of ultrafine (10-100 nm) particles were 2-3 times higher than those reported in the urban areas of North America and Europe. The number fraction of the ultrafine particles to total particle count was also 20-30% higher. The sharp increases in ultrafine particle number concentrations were frequently observed in late morning, and the particle bursts on 5 of the 12 nucleation event days can be attributed to the homogeneous nucleation leading to new particle formation. The new particle formation events were characterized with a larger number of nucleation-mode particles, larger particle surface area, and larger condensational sink than usually reported in the literature. These suggest an intense production of sulfuric acid from photo-oxidation of sulfur dioxide in the YRD. Overall, the growth rate of newly formed particles was moderate (6.4 ± 1.6 nm h-1), which was comparable to that reported in the literature.