Journal cover Journal topic
Atmospheric Chemistry and Physics An interactive open-access journal of the European Geosciences Union
Journal topic

Journal metrics

Journal metrics

  • IF value: 5.668 IF 5.668
  • IF 5-year value: 6.201 IF 5-year
    6.201
  • CiteScore value: 6.13 CiteScore
    6.13
  • SNIP value: 1.633 SNIP 1.633
  • IPP value: 5.91 IPP 5.91
  • SJR value: 2.938 SJR 2.938
  • Scimago H <br class='hide-on-tablet hide-on-mobile'>index value: 174 Scimago H
    index 174
  • h5-index value: 87 h5-index 87
Volume 16, issue 22
Atmos. Chem. Phys., 16, 14131–14145, 2016
https://doi.org/10.5194/acp-16-14131-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.
Atmos. Chem. Phys., 16, 14131–14145, 2016
https://doi.org/10.5194/acp-16-14131-2016
© Author(s) 2016. This work is distributed under
the Creative Commons Attribution 3.0 License.

Research article 15 Nov 2016

Research article | 15 Nov 2016

Particulate matter (PM) episodes at a suburban site in Hong Kong: evolution of PM characteristics and role of photochemistry in secondary aerosol formation

Yi Ming Qin1, Yong Jie Li2, Hao Wang3, Berto Paul Yok Long Lee3, Dan Dan Huang1, and Chak Keung Chan1,3,4 Yi Ming Qin et al.
  • 1Department of Chemical and Biomolecular Engineering, Hong Kong University of Science and Technology, Hong Kong, China
  • 2Department of Civil and Environmental Engineering, Faculty of Science and Technology, University of Macau, Taipa, Macau, China
  • 3Division of Environment, Hong Kong University of Science and Technology, Hong Kong, China
  • 4School of Energy and Environment, City University of Hong Kong, Hong Kong, China

Abstract. Episodes with high concentrations of particulate matter (PM) across the seasons were investigated during four 1-month campaigns at a suburban site in Hong Kong. High-resolution time-of-flight aerosol mass spectrometer (HR-ToF-AMS) measurements revealed that both regional transport and secondary formation contributed to high PM levels during the episodes at this site. Based on distinct meteorological conditions, episodes were categorized into three types: liquid water content (LWC), solar irradiance (IR), and long-range transport (LRT). Despite the difference in meteorological conditions, all episodes were characterized by a high fraction of sulfate (45–56 %) and organics (23–34 %). However, aerosols in LWC episodes were less aged, consisting of the lowest fraction of secondary organic aerosol (SOA) and the highest fraction of small particles. Large particles mixed internally while freshly formed small particles mixed externally in LWC episodes. Aerosols in LRT episodes, by contrast, were the most aged and consisted of the highest proportion of low-volatility oxygenated organic aerosol (LVOOA) and the lowest proportion of small particles. Both small and large particles mixed externally in LRT episodes. The highest proportion of semi-volatile oxygenated organic aerosol (SVOOA) and a medium proportion of small particles were observed in IR episodes. Both small and large particles were likely externally mixed during IR episodes. Furthermore, aerosols experienced the most dramatic size increase and diurnal variation, with a time lag between SVOOA and LVOOA and a gradual increase in carbon oxidation state (OSc ≈ 2 × O : C − H : C). Five out of 10 episodes were of the IR type, further reflecting the importance of this type of episode. The evolution of aerosol components in one particular episode of the IR type, which exhibited a clear land–sea breeze pattern, was examined in detail. Sulfate and SOA due to photochemical aging were very efficiently produced during the course of 6 h. The “less-oxidized” SOA (SVOOA) was initially formed at a higher rate than the “more-oxidized” SOA (LVOOA). The SVOOA transformed to LVOOA at the later stage of photochemical aging. This transformation was further supported by mass spectral analysis, which showed an increase in the most oxidized ion (CO2+) and decreases in moderately oxidized ones (C2H3O+, C3H3O+ and C3H5O+). By measuring the physical and chemical properties of PM in a highly time-resolved manner, the current study was able to demonstrate the dynamic and complex nature of PM transformation during high-PM episodes.

Publications Copernicus
Download
Short summary
The source, formation, transformation mechanisms and mixing state of particulate matter (PM) in high episodic events under different meteorological conditions in Hong Kong remain unclear. With high-resolution time-of-flight aerosol mass spectrometric measurement, we successfully demonstrated the dynamic and complex nature of PM transformation during high-PM episodes. This study revealed that not only regional transport but also local secondary formation is the culprit for high PM levels.
The source, formation, transformation mechanisms and mixing state of particulate matter (PM) in...
Citation