Ka-Ming Wai

Lands Department of The Government of the Hong Kong Special Administrative Region, Hong Kong, Hong Kong

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Publications (6)13.63 Total impact

  • Source
    Ka-Ming Wai, Peter A Tanner
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    ABSTRACT: Springtime regional CO variability in the boundary layer and lower free troposphere in recent years has been studied by a combination of chemical transport models, satellite retrievals and surface-based measurements. Based upon the surface-level measurements and satellite observations, the CO mixing ratios and column densities downwind of the continental outflow were found to have significant reductions in the springtime of 2009 and 2010. Under the influence of continental outflow, there were 58% and 38% decreases in the monthly mean mixing ratios at a rural coastal site in March and April 2009–10, respectively, compared to the 2007–08 figure. Other than the global economic recession, the CO reductions downwind are attributed to the recent implementation of effective anthropogenic CO emissions control in China. The CO simulations by the MM5-CMAQ modeling system with fixed annual emissions support this argument. Features of frontal passage, including the higher CO mixing ratios in the post-frontal stage, were well-captured by the modeling system. The high-resolution nested-grid GEOS-Chem model was used to better characterize the downwind influences of CO due to the biomass burning in Southeast Asia in March and April 2008. The computed CO mixing ratios agreed well with satellite observations at 700 hPa during selected episodes when intense biomass burning activities in Southeast Asia were observed by the satellite images. The biomass-burning-derived CO provided a large contribution (33–86%) to the total CO mixing ratio in the lower free troposphere downwind over the South China Sea and western Pacific Ocean, based on the modeling results. Vertical export of CO in active convection events near the source region was evident.
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    ABSTRACT: Totally 117 cloud/fog water samples were collected at the summit of Mt. Tai (1534m a.s.l.)-the highest mountain in the Northern China Plain. The results were investigated by a combination of techniques including back trajectory model, regional air quality and dust storm models, satellite observations and Principal Component Analysis. Elemental concentrations were determined by Inductively Coupled Plasma Mass Spectrometry, with stringent quality control measures. Higher elemental concentrations were found at Mt. Tai compared with those reported by other overseas studies. The larger proportions and higher concentrations of toxic elements such as Pb and As in cloud/fog water compared with those in rainwater at Mt. Tai suggests higher potential hazards of cloud/fog water as a source of contamination in polluted areas to the ecosystem. Peak concentrations of trace elements were frequently observed during the onset of cloud/fog events when liquid water contents of cloud/fog water were usually low and large amount of pollutants were accumulated in the ambient air. Inverse relationship between elemental concentrations and liquid water contents were only found in the samples with high electrical conductivities and liquid water contents lower than 0.3gm(-3). Affected mainly by the emissions of steel industries and mining activities, air masses transported from south/southwest of Mt. Tai were frequently associated with higher elemental concentrations. The element Mn is attributed to play an important role in the acidity of cloud/fog water. The composition of cloud/fog water influenced by an Asian dust storm event was reported, which was seldom found in the literature.
    Chemosphere 04/2012; 88(5):531-41. · 3.14 Impact Factor
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    ABSTRACT: During a 2009 investigation of the transport and deposition of trace elements in southern China, 37 event-based precipitation samples were collected at an observatory on Mount Heng, China (1,269 m asl). Concentrations of trace elements were analyzed using inductively coupled plasma-mass spectrometry and the wet deposition fluxes were established. A combination of techniques including enrichment factor analysis, principal component analysis, and back trajectory models were used to identify pollutant sources. Trace element concentrations at Mount Heng were among the highest with respect to measured values reported elsewhere. All elements were of non-marine origin. The elements Pb, As, Cu, Se, and Cd were anthropogenic, while Fe, Cr, V, Ba, Mn, and Ni were of mixed crustal/anthropogenic origin. The crustal and anthropogenic contributions of trace elements were 12.8 % (0.9 ~ 17.4 %) and 87.2 % (82.6 ~ 99.1 %), with the maximum crustal fraction being 17.4 % for Fe. Coal combustion, soil and road dust, metallurgical processes, and industrial activities contributed to the element composition. Summit precipitation events were primarily distant in origin. Medium- to long-range transport of trace elements from the Yangtze River Delta and northern China played an important role in wet deposition at Mount Heng, while air masses from south or southeast of the station were generally low in trace element concentrations.
    Environmental Science and Pollution Research 03/2012; 19(8):3389-99. · 2.62 Impact Factor
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    ABSTRACT: Dry deposition samples collected during 1999-2001 at a South China site using surrogate surfaces were analyzed by capillary electrophoresis. Collector surface properties played important roles to the dry deposition. The deposition velocities for various species ranged from 0.02 to 1.69 cm s(-1), in general agreement with literature values. More than 90% of Ca(2+) was deposited by sedimentation and its comparable values of dry or wet removal residence times imply that dry deposition is an important atmospheric removal process for the ubiquitous crustal species in South China, compared with precipitation scavenging. Relatively good agreement was found when the species deposition velocities were modeled based on up-to-date knowledge of particle dry deposition. The total depositions for anthropogenic and crustal species in northern China are likely to be much higher than those in the south, including our site where the fluxes of the acidic species SO(4)(2-) and NO(3)(-) were 4.4 and 2.2 g m(-2) year(-1), respectively. The sum of dry deposition for cations Na(+), Ca(2+), Mg(2+), and K(+) contributes 44% of the total flux, which is equivalent to the value estimated in Europe.
    Environmental Monitoring and Assessment 05/2009; 164(1-4):143-52. · 1.59 Impact Factor
  • Ka-Ming Wai, Peter A. Tanner
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    ABSTRACT: Four-year (1998–2001) data sets of chemical species in particulate matter of 10 μm in diameter or less (PM10) from a monitoring site in a south China coastal city, Hong Kong, comprising major crustal, marine, and anthropogenic species have been analyzed with respect to synoptic-scale and mesoscale meteorological patterns. Their relationships are discussed using surface pressure maps, back trajectory analysis, chemical transport modeling results, and other relevant meteorological data. The mean concentrations of K+, non-sea-salt sulfate (nss-SO42−), and NO3− in aerosols differed from that at a background site by no more than 15%, exemplifying the contributions of major sources from outside Hong Kong. Continental air masses associated with the East Asian winter monsoon always contain high contents of mineral dust and anthropogenic species such as nss-SO42− when they pass over the desert/loess areas and urban cities/heavy industrial areas of mainland China before reaching Hong Kong. Clear decreasing temporal trends of the concentrations of the anthropogenic species nss-SO42− and NO3− are evident during the sampling period. Emissions from biofuel combustion are mixed with urban/industrial plumes before reaching Hong Kong. Wet scavenging significantly depletes the concentrations of chemical species. Marine air masses associated with the summer monsoon or high-pressure systems near Japan always contain large amounts of sea-salt species, but there are noticeably different concentrations of crustal and anthropogenic species between these two weather patterns. The species K+, as a tracer for biomass burning, approaches background levels for summer monsoon air masses originating from Southeast Asia. The proximity and the arrival of the tropical cyclone reflect two extremes (very high/low) species levels. Stagnant air is not the only factor to govern the elevated species levels in aerosols, but the nature of air masses affecting Hong Kong before sampling should also be taken into consideration.
    Journal of Geophysical Research 01/2005; 110. · 3.17 Impact Factor
  • Ka-Ming Wai, Peter A Tanner
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    ABSTRACT: Five-year PM10 data sets from three monitoring stations at a coastal city of China have been employed, together with surface pressure maps, wind data and backward trajectory analyses to investigate the relationship between sea salt concentration (C) and wind speed (U). A log-linear variation of sodium ion concentration with wind speed has been obtained (i.e. ln C=aU+b), only under the influence of the Asian summer monsoon, where U is the synoptic wind speed rather than the local wind speed. The values a and b fall into the range of values from previous studies, although the background loading b is relatively small, since the previous studies were carried out on ships or very near to the coastal line rather than in an urban area. The sea salt concentrations are mainly influenced by the production mechanism rather than the transport process.
    Atmospheric Environment 01/2004; 38(8):1167-1171. · 3.11 Impact Factor

Publication Stats

24 Citations
13.63 Total Impact Points

Institutions

  • 2012
    • Lands Department of The Government of the Hong Kong Special Administrative Region
      Hong Kong, Hong Kong
  • 2004–2012
    • The University of Hong Kong
      • Department of Biochemistry
      Hong Kong, Hong Kong
  • 2005–2009
    • City University of Hong Kong
      • Department of Biology and Chemistry
      Chiu-lung, Kowloon City, Hong Kong