Articles | Volume 17, issue 4
Research article
22 Feb 2017
Research article |  | 22 Feb 2017

Observations of aerosol optical properties at a coastal site in Hong Kong, South China

Jiaping Wang, Aki Virkkula, Yuan Gao, Shuncheng Lee, Yicheng Shen, Xuguang Chi, Wei Nie, Qiang Liu, Zheng Xu, Xin Huang, Tao Wang, Long Cui, and Aijun Ding

Abstract. Temporal variations in aerosol optical properties were investigated at a coastal station in Hong Kong based on the field observation from February 2012 to February 2015. At 550 nm, the average light-scattering (151 ± 100 Mm−1) and absorption coefficients (8.3 ± 6.1 Mm−1) were lower than most of other rural sites in eastern China, while the single-scattering albedo (SSA  =  0.93 ± 0.05) was relatively higher compared with other rural sites in the Pearl River Delta (PRD) region. Correlation analysis confirmed that the darkest aerosols were smaller in particle size and showed strong scattering wavelength dependencies, indicating possible sources from fresh emissions close to the measurement site. Particles with Dp of 200–800 nm were less in number, yet contributed the most to the light-scattering coefficients among submicron particles. In summer, both ΔBC / ΔCO and SO2 / BC peaked, indicating the impact of nearby combustion sources on this site. Multi-year backward Lagrangian particle dispersion modeling (LPDM) and potential source contribution (PSC) analysis revealed that these particles were mainly from the air masses that moved southward over Shenzhen and urban Hong Kong and the polluted marine air containing ship exhausts. These fresh emission sources led to low SSA during summer months. For winter and autumn months, contrarily, ΔBC / ΔCO and SO2 / BC were relatively low, showing that the site was more under influence of well-mixed air masses from long-range transport including from South China, East China coastal regions, and aged aerosol transported over the Pacific Ocean and Taiwan, causing stronger abilities of light extinction and larger variability of aerosol optical properties. Our results showed that ship emissions in the vicinity of Hong Kong could have visible impact on the light-scattering and absorption abilities as well as SSA at Hok Tsui.

Short summary
Multi-year observations at a coastal station in Hong Kong reveals that aerosol optical properties showed clear temporal variations according to the dominant sources of aerosols. LPDM modeling and correlation analysis gave similar signals about the freshness of aerosols during different seasons. Fresh emissions of particles from nearby cities and ship exhausts affected light optical properties and particle size in summer and aged air mass in winter caused larger variability of light extinction.
Final-revised paper