Aerosol number size distribution and new particle formation at a rural/coastal site in Pearl River Delta (PRD) of China

Continuous measurements of aerosol number size distribution in the range of 3 nm–10 μm were performed in Pearl River Delta (PRD), China. These measurements were made during the period of 3 October to 5 November in 2004 at rural/coastal site, Xinken (22°37′N, 113°35′E, 6 m above sea level), in the south suburb of Guangzhou City (22°37′N, 113°35′E, 6 m above sea level), using a Twin Differential Mobility Particle Sizer (TDMPS) combined with an Aerodynamic Particle Sizer (APS). The aerosol particles at Xinken were divided into four groups according to the observation results: nucleation mode particles (3–30 nm), Aitken mode particles (30–130 nm), accumulation mode particles (130–1000 nm) and coarse mode particles (1–10 μm). Concentrations of nucleation mode, Aitken mode and accumulation mode particles were observed in the same order of magnitude (about 10,000 cm−3), among which the concentration of Aitken mode particle was the highest. The Aitken mode particles usually had two peaks: the morning peak may be caused by the land–sea circulation, which is proven to be important for transporting aged aerosols back to the sampling site, while the noon peak was ascribed to the condensational growth of new particles. New particle formation events were found on 7 days of 27 days, the new particle growth rates ranged from 2.2 to 19.8 nm h−1 and the formation rates ranged from 0.5 to 5.2 cm−3 s−1, both of them were in the range of typical observed formation rates (0.01–10 cm−3 s−1) and typical particle growth rates (1–20 nm h−1). The sustained growth of the new particles for several hours under steady northeast wind indicated that the new particle formation events may occur in a large homogeneous air mass.