Particle number size distribution of dustfall aerosol in the suburban area of Hefei

The observation of particle number concentration and size distribution was performed from March 20 to 28, 2010 in Hefei suburban area. The observation period includes the entire sequence of dustfall period, intermittent rainy period, and sunny period which is benefit for the formation of new particles. The analysis of particle number concentration shows that the concentration of Nucleation mode (5 similar to 20 nm), Aitken mode (20 similar to 100 nm) and Accumulation mode (100 similar to 1000 nm) particles during dustfall period was 898 cm(-3), 3424 cm(-3), and 1587 cm(-3), respectively, not obviously higher than those of intermittent rainy (255 cm(-3), 1509 cm(-3), 1213 cm(-3)) and sunny period (706 cm(-3), 4891 cm(-3), 2468 cm(-3)), but the concentration of Coarse mode particles during dustfall period (48 cm(-3)) was much higher than that in other periods. The observational results also show that the curves of aerosol particle number size distribution of Hefei are in two-peak pattern. The first peak appears between 10 similar to 20 nm, while the second peak appears near 100 nm. The peaks appear at slightly different positions under different weather conditions. During dustfall period, the number concentration of particle with diameter below 10 nm and above 400 nm is higher than those of other period, not just for Coarse mode particles with diameter above 1 mu m.