Observation of aerosol size distribution and new particle formation at a mountain site in subtropical Hong Kong

Abstract

Abstract. In order to investigate the atmospheric particle formation and growth processes, and to quantify the particle number (PN) concentration and size distributions in Hong Kong, a three-month intensive field measurement was conducted from September to November in 2010 near the mountain summit of Tai Mo Shan, a suburban site approximately the geographical centre of the New Territories in Hong Kong. The mean total number concentration in the size range of 5.5–350 nm was 7.86 ± 0.66 × 103 cm−3 (mean ± 95% confidence interval), with a maximum value in November. New particle formation (NPF) events were observed on 12 out of 35 days in October/November 2010 with the formation rate from 0.29 to 4.53 cm−3 s−1, and the average growth rates from 1.53 to 9.44 nm h−1. The events usually began at 10:00 ~ 11:00 local time characterized by the occurrence of a nucleation mode with a peak diameter of 6 ~ 10 nm. The observed linear or non-linear correlations between nucleation mode PN concentration (5.5–10 nm) and ozone, volatile organic compounds (VOCs) and/or (UV × SO2) suggested critical roles of sulfuric acid and biogenic VOCs (e.g. isoprene, α-pinene and β-pinene) in the NPF events.