Alexis Kai Hon Lau

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Secondary organic carbon (SOC) is often a significant portion of organic carbon (OC) in ambient particulate matter (PM). The levels and seasonal patterns of SOC in Hong Kong were examined using more than 2000 PM 10 measurements made over a 4.5-year period (1998–2002) in a network of ten air quality monitoring stations. The positive matrix factorization(More)
The aerosol extinction-to-backscatter ratio is an important parameter for inverting LIDAR signals in the LI-DAR equation. It is a complicated function of the aerosol microphysical characteristics. In this paper, a method to retrieve the column-averaged aerosol extinction-to-backscatter ratio by constraining the aerosol optical depths (AOD) from a(More)
Secondary organic carbon (SOC) is often a significant portion of organic carbon (OC) in ambient particulate matter (PM). The levels and seasonal patterns of SOC in Hong Kong were examined using more than 2000 PM 10 measurements made over a 4.5-year period (1998–2002) in a network of ten air quality monitoring stations. The positive 5 matrix factorization(More)
Ambient measurements of seventeen 2,3,7,8-polychlorinated dibenzo-p-dioxin/dibenzofuran congeners (2,3,7,8-PCDD/Fs) have been taken in a number of monitoring programs or ad-hoc studies in Hong Kong. The longest monitoring program started at two locations in the territory in July 1997. The other monitoring efforts are ad-hoc studies, varying from a few(More)
As one of the most notorious atmospheric pollutants, NOx not only promotes the formation of ozone but also has adverse health effects on humans. It is therefore of great importance to study the sources of NOx and its effects on human health. The Comprehensive Air Quality Model (CAMx) modeling system and ozone source apportionment technology (OSAT) were used(More)
School age children are particularly susceptible to exposure to ambient fine particle (PM2.5). To provide insight into factors affecting variability in ambient PM2.5 exposure, distributions of daily PM2.5 exposures for school age children are estimated for four seasons in three climatic zones of the United States using a stochastic microenvironmental(More)
The aerosol extinction-to-backscatter ratio is an important parameter for inverting LI-DAR signals in the LIDAR equation. It is also a complicated function of aerosol micro-physical characteristics depending on geographical and meteorological conditions. In this paper, a method to retrieve the column-averaged aerosol extinction-to-backscatter 5 ratio by(More)
In recent years in a few Chinese megacities, fog events lasting one to a few days have been frequently associated with high levels of aerosol loading characterized by high sulfate (as high as 30 μg m(-3)), therefore termed as haze-fog events. The concomitant pollution characteristics include high gas-phase mixing ratios of SO2 (up to 71 ppbv) and NO2 (up to(More)
This paper describes a simple but practical methodology to identify the contribution of primary and secondary air pollutants from the local/regional emission sources to Hong Kong, a highly urbanized city with complex terrain and coastlines. The meteorological model MM5 coupled with a three-dimensional, mutli-particle trajectory model 5 is used to identify(More)
Volatile organic compounds (VOCs) were measured at four stations with different environments in Hong Kong (HK) during two sampling campaigns. Positive matrix factorization was applied to characterize major VOC sources in HK. Nine sources were identified, and the spatial and seasonal variations of their contributions were derived. The most significant local(More)