Re ECF Project: 2008-20

Project Title: Quantitative measurement of acidic ultrafine particles in the atmosphere

Applicant: The Hong Kong Polytechnic University (Dr. GUO Hai)

Total Approved Grant: $1,279,360

Duration: 4/1/2010 to 3/1/2013

Project Status/Remarks: Completed

The overall purpose of this proposal is to develop a novel method to quantify the number concentration of acidic ultrafine particles in the air. The specific scientific objectives are:

  • to develop a nanofilm detector for the collection of ambient acidic ultrafine particles;
  • to design an ultrafine diffusion monitor with high collection efficiency in which the nanofilm detector can be placed for sampling;
  • to modify and utilize an electrical precipitation sampler with the placement of the detectors which has a high collection efficiency;
  • to carry out field measurements at roadside and residential sites in Hong Kong to assess the reliability and efficiency of the ultrafine particle samplers, and
  • to determine the abundance, spatial and temporal variations of acidic ultrafine particles in Hong Kong.

Summary of the Findings/Outcomes:
The mean ultrafine particles (UFPs) and acidic UFPs number concentrations at the four sites were all higher in cold seasons than that in warm seasons, indicating the meteorological conditions played an important role on the temporal variations of acidic UFPs concentration. Lower acidic UFPs number concentrations were observed at the TMS sit and the HT site (rural or background site) and higher acidic UFPs number concentrations were found at HH site and the TC site (urban sites). And acidic UFPs counted for more fractions of PN concentrations (32.5% - 42.9%) in polluted urban areas than that (21.1% - 30.1%) in relatively clean areas. By investigating the spatial variations of acidic UFPs at these urban, rural and background sampling sites in Hong Kong, the project team found remarkable differences in the acidic UFP’s number levels between the rural/background sites and the urban sites. At the urban sites, the levels of acidic UFPs were almost 5-7 times as high as that at the rural /background sites in both cold and warm seasons. This may reflect the traffic impact on the increased levels of acidic UFPs at the urban sites.