Air Pollution Modeling

Dr. Nicky Y. F. LAM
Tel: 3442-9625
Email address

The focuses are on regional and local air pollution modeling, long-range transport of air pollutants, and global climate and air quality downscaling.  Our outgoing research projects can be categorized into four main areas:
1. Air quality modeling and studies
2. Studies on climate change and the Urban Heat Island (UHI) effect
3. Emission Inventory Development
4. Dispersion of atmospheric pollutants in urban environments

A Study of the Impact of Southeast Asia Biomass Burning - The 7 SEAS Project

Biomass burning is a significant source of carbon monoxide and particulate matter, which not only contributes to local air pollution, but also regional air pollution. This study investigates the impacts of biomass burning emissions from Southeast Asia (SEA) on air pollution in the East and South China Sea (ECSC) region, including Hong Kong and Taiwan.  Using the Weather Research & Forecasting (WRF), Community Multi-scale Air Quality (CMAQ) and Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) models, research work is being carried out in three phases:
1. Evaluating the contribution of SEA biomass burning to the background pollutant concentration in the ECSC area,
2. Developing a method to identify the potential events resulting from SEA biomass burning, and
3. Assessing the potential impacts of SEA biomass burning on the ECSC.

A Study of Stratospheric-Tropospheric Exchange (STE) of Ozone

This study focuses on investigating the relationship between tropospheric ozone and stratospheric-tropospheric exchange (STE) in North America and East Asia from 1995 to 2014.  Data analysis has been carried out using 96 selected monitoring sites from a total of four datasets from the World Ozone and Ultraviolet Radiation Data Centre (WOUDC), the Clean Air Status and Trends Network (CASTNET), the Hong Kong Environmental Protection Department (HKEPD) and Acid Deposition Monitoring Network in East Asia (EANET). 

It was found that among the selected sites in North America and East Asia, the tropospheric ozone concentration had a positive correlation with both the altitude and latitude due to higher STE.  Furthermore, it was also discovered that, for higher altitudes and latitudes (e.g. remote areas of the United States and Japan), the ozone concentration peaked around April (Figures 1 and 2), reflecting a higher ozone STE in these areas during springtime.

Figure 1. Average Monthly Ozone Concentration of Selected Sites in the US.

Figure 2. Average Monthly Ozone Concentration of Selected Sites in Japan.

Evaporative VOCs from Passenger Vehicles in China and Hong Kong

Due to the sharp increase of automobile population, evaporative VOCs from passenger vehicles has become a problematic issue in China that requires more attention. Depending on the emission control systems and technology standards (e.g. Euro1, Euro2, etc.), passenger vehicle fuel tanks produce different levels of VOC emissions that can lead to air pollution and health impacts. For outdoor parking, the diurnal temperature has a positive correlation with the temperature of fuel tanks and is one of the main factors affecting the rate of evaporative VOCs emissions. In order to have a better understanding for air pollution management, this study investigates the effect of the major factors (e.g. emission standards and air temperature) that are related to evaporative VOCs emissions from passenger vehicles in China and Hong Kong.

Impacts of tropical cyclone changes on Hong Kong air quality

This project investigates the changes in tropical cyclones (TC) in the western North Pacific (WNP) caused by change in weather patterns and their effects on the air quality in Hong Kong.  Based on TC track records from the Hong Kong Observatory from 1991 to 2010, a decrease of TC track density has been observed in the South China Sea (region 1) and east of the Philippines (region 3), while an increase of TC track density has been found in the vicinity of Taiwan (region 2).  Analysis using Hong Kong EPD air quality data shows a positive correlation of the number of episodic days in Hong Kong due to high ozone level with this TC track change.  From regional atmospheric circulation, this has been found to be the result of the large amount of air pollutants transported to Hong Kong from the industrial areas of the Pearl River Delta during TC occurrence near Taiwan.  Further investigation will be carried out to take into consideration other factors that may affect the local air quality during TC occurrences, including the TC intensity and the local meteorological conditions.

Simulation study on the impact of tree-configuration, planting pattern and wind condition on street-canyon's thermal comfort and air quality

To understand the impact of tree-configuration, planting pattern and wind condition on street-canyon's thermal comfort and air quality (dispersion-deposition), numerical experiments involving street canyons of varying aspect ratio (ARB) with embedded trees of varying aspect ratio (ART), leaf area index (LAI), leaf area density (LAD) distribution and trunk height under different wind conditions were conducted using ENVI-met model.  Results have shown that characterization of trees based on leaf area index (LAI) may not be perfectly appropriate because different magnitude of thermal comfort improvement and 'tree-impact' on air quality was observed with different LAD distribution, even though they are of the same LAI.  Furthermore, results reveal that trunk height variation does not generally affect thermal comfort but lower trunk height helps increase the magnitude of air quality benefit.  It is therefore recommended that trees with lower trunk heights should be favored instead of their higher counterparts.

Urban Weather Research and Forecasting (WRF) model on visibility and the Urban Heat Island effect

The purpose of this study is to improve the visibility prediction in Hong Kong by taking the Urban Heat Island (UHI) effect into account. In this project, the Multi-layer urban canopy model (M-UCM) is used to simulate the complex terrain of Hong Kong. By providing more accurate meteorological outputs (e.g. wind and surface temperature) to the Community Multi-scale Air Quality (CMAQ) model, the results contribute to better predictions on the visibility of Hong Kong.

Pollutant prediction in Kwun Tong, Hong Kong after implementing the M-UCM and the new emission data (2010)

Mitigation of the Urban Heat Island effect in Hong Kong using open river systems

The Urban Heat Island (UHI) effect comes with urbanization as a result of replacement of natural surfaces by built-up environment.  In a densely populated city such as Hong Kong, UHI contributes significantly to the rise in temperature within the urban areas.  In this study, temperature data from rural and urban stations of the Hong Kong Observatory are compared in order to analyze the UHI effect in Hong Kong, and the Shing Mun River in Shatin is used to investigate how an open river system affects the UHI effect in the area.  A modeling software, ENVI-met, is also used to study the mitigating effect of an open river system to the UHI effect in various building scenarios and settings along the water body.

Redevelopment of Top-Down Emission Inventory Using ArcGIS

In this project, an updated emissions inventory using a top-down emission allocation approach (Du, 2009) will be developed for supporting air pollution forecast services in Hong Kong and China.  The inventory will consist of different emission sectors, namely, Electrical Generation Units (EGUs), Large Point Source (LPS), industrial source, ship emission, road transportation and residential source.  For supporting fine-resolution (3 x 3 km grid) modelling, a novel industrial source allocation method using newly tested image processing techniques on satellite images will be developed (Lam, 2016), while other sectorial emissions will be processed through the data and methodology described in Du (2009) and Li (2015) using the Geographical Information System (i.e., ArcGIS).   The final results of the emissions allocation will form a useful basis for fine-resolution air quality forecasts in Asia. 

References:

1.      Y. DU, Y. F. LAM, J. S. FU (2009), 2006 Updated Asian Emission Input for CMAQ & CAMx Fine Resolution Simulation, Air and Waste Management Annual Conference, Detroit, MI, USA, June 17-20.

2.      M. LI, Q. Zhang, J. Kurokawa and et al., (2015) MIX: a mosaic Asian anthropogenic emission inventory for the MICS-Asia and the HTAP projects, Atm. Chem. & Phys. Discussions, 27 November. Doi:10.5194/acpd-15-34813-2015.

3.      Y. F. LAM, S. L. CHEUNG, C. YANG and T. S. CHOY (2016), Top-down emission inventory development for fine resolution simulation, Atmospheric Modeling Research in East Asia (MICS-Asia), Chengdu, Sichuan, China, Feb 29-Mar 2.

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Vertical profile of atmospheric pollutants in different urban settings in Hong Kong

In a densely populated city like Hong Kong, high pollutant emissions often result in high air pollution levels due to the low dispersion potential in the closely packed built environment.  For example, in a street canyon, the air flow may be highly inhibited by the tall buildings on both sides of the street and dispersion of air pollutants may become very slow.  In different areas of Hong Kong, the dispersion characteristics of atmospheric pollutants can also be affected by the different topographies of the complex terrain (e.g. lowland, upland, coastal regions) and the resulting vertical profiles of air pollutant concentrations will also vary.  In order to assess the human exposure to air pollution and the health risks involved, it is necessary to have a better understanding on the vertical profile the atmospheric pollutants and its relationship with the various urban settings.

 

In previous studies, atmospheric pollutant dispersion and vertical profiles in urban environments were often simulated using Computational Fluid Dynamics (CFD) models.  However, due to lack of field data, it is often difficult to validate the simulation results.  Remote sensing techniques such as Differential Optical Absorption Spectroscopy (DOAS) can be used for measuring atmospheric pollutant concentrations but they are generally difficult to apply to large numbers of measurement locations on different elevations.  In this project, an experimental method for establishing the vertical profile is adopted using Tedlar bags for collecting air samples on different elevations and the Cavity-Enhanced Differential Optical Absorption Spectroscopy (CE-DOAS) instrument measuring the pollutant concentration.



Team members (Clemens and Helen) collecting air samples and recording meteorological data on the upper floors of Mei Yue House, Shek Kip Mei Estate on 26 April, 2016.

The first phase of this project focuses on developing vertical profiles of nitrogen dioxide (NO2) in various urban settings.  NO2 is a major air pollutant from road traffic that can produce adverse health effects and is also a precursor of ozone.  The experimental results will provide a better understanding of NO2 vertical dispersion in various urban settings by investigating the various factors including road traffic, building and street configurations, land topography and the meteorological conditions. The vertical profile data will also help to determine a suitable value for the diffusivity coefficient (Kz) for CFD modelling and validating the simulation results.