Observation of aerosol size distribution and new particle formation at a coastal city in the Yangtze River Delta, China

Abstract

Aerosol number size distribution in the range of 10 nm–10 μm, trace gases (O3, CO, SO2 and NO2), particular matter (PM: PM2.5 and PM10) and meteorological elements were measured from the 1st to the 31st of May, 2015, in the coastal city of Jiaxing in the Yangtze River Delta (YRD). The average number concentration and surface area concentration were 19,639 cm− 3 and 427 μm2 cm− 3 during the observation period. The different mode particle concentrations ranked in the order of Aitken mode (12,361 cm− 3) > nucleation (4926.7 cm− 3) > accumulation (2349.3 cm− 3) > coarse mode (1.7 cm− 3). The average concentrations of CO, SO2, NO2, O3, PM2.5 and PM10 were 0.545 mg m− 3, 14.7, 35.1, 89.8, 43.5 and 64.6 μg m− 3, respectively. Eight precipitation processes and 15 new particle formation (NPF) events (3 NPF events occurred on a rainy day) were observed. Results show that the precipitation process had greater scavenging effects on particles smaller than 120 nm and larger than 2 μm. The spectral distributions of number concentrations were unimodal at different weather conditions, with peaks at 20 nm, 40–60 nm, 50–80 nm on NPF days, rainy days and normal days. During the NPF events, the formation rate (FR), growth rate (GR), condensational sink (CS), vapor source rate (Q) and condensing vapor concentration (C) were in the range of 4.0–17.0 cm− 3 s− 1, 2.2–15.7 nm h− 1, 1.5–5.8 × 10− 2 s− 1, 0.5–7.7 × 106 cm− 3 s− 1 and 3.0–21.5 × 107 cm− 3, with mean values of 9.6 cm− 3 s− 1, 6.8 nm h− 1, 3.4 × 10− 2 s− 1, 3.3 × 106 cm− 3 s− 1 and 9.4 × 107 cm− 3, respectively. NPF events normally occurred under clean atmospheric conditions with low PM concentrations but high levels of trace gases. It was also found that SO2 plays an important role in NPF and growth in Jiaxing.