4.                         AIR QUALITY IMPACT ASSESSMENT

4.1                      Introduction


4.1.1                 A Comprehensive Development was proposed in Yau Tong Bay area. In accordance with the Environmental Impact Assessment (EIA) ordinance procedure for a designated project, an application for a study brief was submitted to EPD in January 1999 for the proposed development. The study brief issued by EPD in February 1999 (Brief no.: ESB-0028/1999) stated that an air quality impact assessment should be conducted as part of the EIA study.

4.1.2                 This Air Quality Impact Assessment shall form part of the EIA report for the proposed development. The air quality impact assessment has quantitatively assessed the emission impacts from industrial stack sources, vehicular sources, portal and ventilation shaft emissions from the Eastern Harbour Crossing (EHC) Tunnel, and their cumulative impact upon the development. Potential odour impact from a temporary sewage retention tank within the site has also been assessed.  A figure showing an emission sources are shown in Appendix 4A.

4.1.3                 Appropriate mitigation measures were recommended and have been adopted in the Master Layout Plan design to meet relevant environmental standards and to minimise any unacceptable impacts, if any.

The Proposed Development and its Environs

4.1.4                 The subject site at Yau Tong, East Kowloon, has a total area of 28.5 hectares in Full Reclamation option (21.5 hectares in Minimised Reclamation option). It comprises of 42 Yau Tong Marine Lots (YTML), 2 government lots, and 18 ha (12 ha for Minimised Reclamation option) of proposed reclaimed land of Yau Tong Bay. The subject site is north- and east-bounded by Cha Kwo Ling Road, south-bounded by Ko Fai Road, and west-bounded by the proposed Western Coast Road in Full Reclamation or Victoria Harbour in Minimised Reclamation.  It is also located immediately to the north of the Yau Tong Industrial Area.

4.1.5                 The proposed development comprises of thirty-nine high rise residential towers.  The floor-to-floor height of the residential tower is 2.8m, with a street level of 5.5mPD. In addition, the proposed development also includes five primary schools, three secondary schools, one shopping arcade and one office tower.  The master layout plans of the development options can be found in Figures 5.3a – f.

4.1.6                 The portal of Eastern Harbour Crossing (EHC) Tunnel is located at approximately 70m to the north of the subject site. In addition, there a ventilation shaft tower located at approximately 10m aboveground adjacent to the north-western corner of the subject site which emit approximately 70% of the traffic emissions from the tunnel by mechanical extractions. Technical information pertaining to the ventilation system was provided by New Hong Kong Tunnel Company Limited.

4.1.7                 While conducting this EIA, a new road link from Tseung Kwan O to eastern Kowloon, namely Western Coast Road (WCR) was being studied by Territory Development Department (TDD).  Two alignment options were being considered by the department:

·       The Coastal Option – elevated roadway along the south eastern coastline of Kowloon stretching from eastern Kowloon to Tseung Kwan O.

·       The Tunnel Option – a tunnel connecting east Kowloon and Tseung Kwan O WCR with one exit at Cha Kwo Ling and the other in Tiu King Lang.

4.2                      Assessment Criteria

4.2.1                 The assessment criteria for air pollution control are based on Air Quality Objectives (AQOs) as required by Annex 4 of the Technical Memorandum on Environmental Impact Assessment Process (TM). Sulphur Dioxide (SO2), nitrogen dioxide (NO2) and respirable suspended particulate (RSP) have been chosen as the representative pollutants for assessment of air quality impact from industrial and vehicular emissions. The standards for SO2, NO2 and RSP levels adopted throughout the assessment are given in Table 4.1.

Table 4.1     Hong Kong Air Quality Objectives for Pollutants


Pollutants concentration in µg/m3


Averaging Time


1 hour (i)

8 hours (ii)

24 hours (ii)

1 year (iii)

















(i)       Not to be exceeded more than 3 times per year

(ii)      Not to be exceeded more than once per year

(iii)      Arithmetic means

4.3                      Background Air Quality

4.3.1                 Annual average concentrations of SO2 & NO2 recorded by EPD’s monitoring stations in Kwun Tong in 1999 and RSP in 2000 have been used as background concentrations of the subject site.  (At the time of preparation for this report, background concentrations for the year 2000 have been issued, but values presented for the Kwun Tong monitoring stations for SO2 and NO2 are below their respective minimum data requirement of 66% for number of data within the period, and was therefore considered inappropriate to use.) Table 4.2 summarised the background concentrations of SO2, NO2, and RSP adopted in the assessment for the purpose of evaluating the cumulative air quality impact.

Table 4.2     Background Air Pollutant Levels Adopted in the Assessment

Air Pollutant

Annual Average Concentration (mg/m3)








4.4                      Air Sensitive Receivers

4.4.1                 Air sensitive receivers (ASRs) were selected in accordance with a 30m by 30m grid covering the entire proposed development for assessing all pollutants of concern.

4.4.2                 The variation of SO2 concentration with respect to building height were predicted at 1,500 mm (breathing zone) above every third floors from 1/F (+18.0 mPD) to 43/F (+135.6 mPD) with a base elevation of 5.5 mPD, a podium of 6m and a lift lobby of 5m. Additional assessments were performed for SO2 at the worst affected floors identified from the preliminary assessment, viz. 19/F to 22/F.

4.4.3                 Since vehicular emission shall be the major source for NO2 and RSP impact, concentration at the selected ASRs were assessed at 1.5m above the ground floor (to target the low level air sensitive receivers near street level), first floor of residential units and seventh floor, which is the floor with closest elevation with the WCR for the Coastal Alignment Option. Cumulative NO2 impact at the development from industrial and vehicular emission has been evaluated.

4.4.4                 The predicted pollutants concentrations were then transferred to a separate computer software to create two-dimensional concentration contour maps (isopheths), which were then superimposed onto the master layout plan of the proposed development.

4.4.5                 These contour maps represent the pollutants plume impingement from surrounding industrial and vehicular emissions and the impact upon the future residents can then be evaluated.

4.5                      Meteorological Data

4.5.1                 Meteorological data of Junk Bay Weather Station of the year 1998 obtained from the Hong Kong Observatory have been used in the modelling with ISCST programme. Parameters used include:

·            Hourly wind direction;

·            Hourly wind speed with minimum assumed as 1m/s;

·            Hourly Pasquill stability class (A to F);

·            Hourly ambient air temperature (°K);

·            Morning and afternoon mixing heights (m); and

·            Total sky cover, and sky cover and ceiling height of the 1st - 4th layer.

4.5.2                 The following typical worst case meteorological conditions were assumed in the prediction of vehicular emission impact using CALINE4:

Wind Speed                                                  1 m/s

Stability Class                                              D

Wind Direction                                             Worst case for individual receiver

Wind Direction Standard Deviation             18° for Tunnel Option

                                                                     12° for Coastal Option (refer to Section 4.8.14)

Mixing Height                                               500 m


4.6                      Assessment Methodology

4.6.1                 Air quality impact upon the proposed development at Yau Tong Bay shall comprises of pollutants emitted from nearby industrial stacks and vehicular emissions from busy road networks in the vicinity.

4.6.2                 Therefore, this air quality impact assessment has quantitatively assessed the potential impact from industrial undertakings in the region, as well as from vehicles traveling in the area. In addition, the cumulative impact from both activities, incorporating the background air quality condition, will be predicted for NO2 concentration for comparison with the stipulated AQO.

4.7                      Industrial Air Quality Impact Assessment

Scope of Work

4.7.1                 Air quality impacts due to industrial emissions within 1km radius of the subject site has been calculated with computer modeling.

Source Description and Emissions Inventory

4.7.2                 Industrial operations involving the burning of solid and fossil fuel are major emission sources of anthropogenic SO2 and NO2.  The concentration and dispersion of SO2 and NO2 emission are related to the type and age of the boiler, the type and quantity of fuel consumption, chimney height and size, and the exit temperature of the emission.

4.7.3                 A total number of 36 diesel fuel consuming chimneys have been identified within 1km radius of the subject site from EPD’s register. Locations and characteristics of the chimneys are listed in the ISCST output file included in Appendix 4B.  According to the Air Pollution Control (Fuel Restriction) Regulations introduced on 25th January 1990 under Regulation 43 of the Air Pollution Control Ordinance, sulphur content of liquid fuel is not allowed to exceed 0.5% w/w and a viscosity under 6 centistokes at 40°C. Such restrictions have been applied and used as assumptions in the calculation of the emission strength of the chimneys.

4.7.4                 The emission factor of nitrogen dioxide is based on AP42 (USEPA 1995: table 1-1 Criteria Pollutant Emission Factor for Uncontrolled Fuel Oil Combustion).  Diesel fuel with low nitrogen content is being used in Hong Kong, therefore the emission factor of 0.0024kg/litre has been adopted for the prediction. 

Computer Modeling

4.7.5                 The dispersion of SO2 and NO2 were studied and modeled using the software "Industrial Source Complex Short Term Version 3 (ISCST3)" developed by Trinity Consultants Incorporated. This model is based on the principle of Gaussian dispersion and is widely acceptable by authorities world-wide including the United States Environmental Protection Agency (USEPA) and the Hong Kong Environmental Protection Department (EPD). Selected section of a typical ISCST.LST result file for industrial emission assessment has been enclosed in Appendix 4B for reference.

Interfacing Issue with Yau Tong Industrial Area

4.7.6                 A site inspection was carried out on the existing Yau Tong Industrial Area. It was found that most “industrial” buildings have already been redeveloped into non-pollutant emitting “industrial/office” buildings with a few local restaurants on street level. The development blocks along Ko Fai Road will be set back 30m from the road, thus creating a substantial buffer between the residential blocks and these low pollutants emitting buildings. In consideration of these factors, no significant environmental impact from the industrial/residential interface would be expected.

Assessment Results

4.7.7                 Air quality impact due to industrial emissions from surrounding area have been quantitatively assessed. The predicted highest 1-hour and 24-hour average SO2 levels with background concentration included for every third floor of residential levels are presented graphically in Appendix 4G. Additional assessment was performed at the worst affected floors, viz. 19/F to 22/F, on a floor to floor bases. The assessment results indicate that the predicted SO2 levels at all air sensitive receivers of the subject site are within the relevant AQOs requirements.

4.7.8                 NO2 emission from the industrial stacks is usually not a major pollutant for ambient air due to the relatively low emission rate and high elevation of emission.

4.7.9                 Since the subject site is surrounded by busy road networks, including the existing EHC Tunnel, the NO2 emission from the industrial undertakings in the nearby industrial area were also assessed for quantifying the cumulative NO2 impact at the proposed development from vehicular emission as well as from industrial stacks.  The assessment was conducted for the worst affected floors, i.e. the ground floor and the first floor of residential unit.

4.7.10              The predicted SO2 concentration contours are only presented on “Full Reclamation without I/R Interface” as this scenario contains the basic footprint of the Master Layout Plan, additional residential building blocks located at the I/R interface industrial sites, as well as an additional school site located at the larger reclaimed land. This represents the worst case scenario.

4.8                      Vehicular Emission Impact Assessment

Scope of Work

4.8.1                 The aim of this study is to assess the cumulative air quality impacts arising from traffic emissions affecting the proposed development. These include emissions from the surrounding road network, including vehicles queuing at the toll plaza, as well as the portal of the EHC which is situated at approximately 70m to the north of the proposed development. In addition, there is a ventilation shaft of the EHC located immediately adjacent to the north-western corner of the subject site exhausting approximately 70% of the traffic emissions from the tunnel by mechanical extraction.

4.8.2                 At the time of this EIA, TDD was in the process of investigating the feasibility of various WCR options. To allow flexibility for this assessment and to meet the criteria in the Technical Memorandum on EIA process, air quality impact for both WCR alignment options (tunnel and coastal) were assessed. Each of the alignment options is further divided into two scenarios of with and without I/R interface. The four options are:

WCR Tunnels Options:

·            Minimum Reclamation without I/R Interface

·            Minimum Reclamation with I/R Interface

WCR Coastal Options:

·            Full Reclamation without I/R Interface

·            Full Reclamation with I/R Interface

4.8.3                 The criteria pollutants associated with traffic emission considered in this assessment including nitrogen dioxide (NO2), respirable suspended particulate (RSP).

4.8.4                 Although carbon monoxide (CO) is also a major constituent of traffic emission, based on the emission rates of CO of different types of vehicles, the corresponding AQO of CO, and the general low background level of CO in the Territory, it is envisaged that CO would not be a critical component in the air quality impact. It will meet the AQO automatically, when the criteria for NO2 and RSP at the ASRs are satisfied.

4.8.5                 Some contribution on NO2 emission is expected from the industrial undertakings as mentioned in Section 4.7.9.  These contributions are included in obtaining the overall cumulative NO2 impacts on the proposed development.

4.8.6                 Emissions from open-road traffics have been predicted by use of the model CALINE4. Vehicular emissions from tunnel portal and ventilation exhaust buildings from the Eastern Harbour Crossing (EHC) Tunnel and the tunnel of Tseung Kwan O Western Coast Road, idling traffics at the EHC’s toll plaza section, have been predicted using the ISCST3 model. The modeled results using CALINE4 and ISCST3 at the same ASRs together with the background air pollutant levels have been summed for prediction of the cumulative air quality impact.

4.8.7                 As the maximum hourly pollutant concentrations predicted at the same ASRs by using two independent models may occur under different meteorological conditions and time, a direct summation of the results obtained from the two models could represent a highly conservative scenario in this study.

Traffic Emission from Open Road Traffics

Traffic Flow

4.8.8                 Traffic flow data during morning peak hours of road in the vicinity of the site, including Lei Yue Mun Road, Cha Kwo Ling Road, Cha Kwo Ling Road Diversion, Ko Fai Road, the EHC, the WCR along the western boundary of the site (for the Coast Alignment Option), the tunnel of Tseung Kwan O Western Coast Road (for the Tunnel Option without Ko Fai Road Connection) and the additional flyover from Cha Kwo Ling Road, for the year 2030 have been used in the assessment. This is based on the fact that the proposed development is scheduled to be completely occupied after the year 2016.  Under the current scheme, there is no Ko Fai Road connection.

4.8.9                 The traffic flow data was provided by the Project Traffic Consultant (MVA Hong Kong Limited) with the best available information on the proposed development in the vicinity.

4.8.10              The predicted day-time traffic flow and traffic mix of the surrounding road network prepared by the Project Traffic Consultant are tabulated in Table 4.3 and Table 4.4.

Table 4.3   Traffic Volume and Composition Forecast for the Year 2030 for the Coast Alignment Option


% of Passenger Car

% of Light Goods Vehicle

% of Heavy Goods Vehicle

% of Buses/ Coach

2030 AM Peak

Traffic flow (vehs/hr)

Eastern Harbour Crossing Tunnel






Yau Tong Road Diverted






Cha Kwo Ling Road - East of Yau Tong Road Diverted






Cha Kwo Ling Road - West of Yau Tong Road Diverted






Ko Fai Road






WCR - North of the site






WCR - West of the site






WCR - South of the site






WCR – EB slip road to Ko Fai Road






WCR – WB slip road from Ko Fai Road






WCR – SB slip road from Cha Kwo Ling Road






WCR – NB slip road to Cha Kwo Ling Road






Remark: SB – South Bound; NB – North Bound; EB – East Bound; WB – West Bound

Table 4.4    Traffic Volume and Composition Forecast for the Year 2030 for the Tunnel Option (Without Ko Fai Road Connection)

Road Section

% of Passenger Car

% of Light Goods Vehicle

% of Heavy Goods Vehicle

% of Buses/ Coach

2030 AM Peak

Traffic flow (vehs/hr)

Eastern Harbour Crossing Tunnel






Yau Tong Road Diverted






Cha Kwo Ling Road - East of Yau Tong Road Diverted






Cha Kwo Ling Road - West of Yau Tong Road Diverted






Ko Fai Road






Slip Road from roundabout to tunnel of Tseung Kwan O WCR 






Slip Road to roundabout from tunnel of Tseung Kwan O WCR 






Tunnel of Tseung Kwan O WCR






Slip Road from Road A to roundabout






Slip Road to Road A from roundabout



















Source Types and Emission Strength

4.8.11              Air pollutant levels and dispersions due to traffic emissions are related to factors such as engine operational mode, vehicle type and age, road characteristics, and the distance to allow dispersion of the emitted pollutants.

4.8.12              Vehicle fleet average emission factor of the pollutants have been obtained from the Vehicular Emission Control Section of EPD in August 1999 (EURO III Model), which is latest available emission factors to date. Emission factors for the year 2011 has been used which is in line with the full population intake schedule of 2016. The emission factors are given in Table 4.5.

4.8.13              This is considered a sufficiently conservative approach as the emission factors are expected to decrease in time due to technological advancement and the phasing out of diesel vehicles. Four major categories of vehicle types have been considered in the assessment:

·            Passenger Car (Petrol), (P/C - p)

·            Light Goods Vehicle, (LGV – dl)

·            Heavy Goods Vehicle, (HGV)

·            Bus / Coach (FBDD)


Table 4.5       Emission Factors of the Vehicular Pollutants Concentration for the year 2011

Vehicle Type

Emission Factor ( g/km)-EURO III MODEL




Passenger Car (Petrol), (P/C - p)



Light Goods Vehicle (LGV - dl)



Heavy Goods Vehicle (HGV)



Bus / Coach (FBDD)



A vehicle composition weighted emission factor was calculated with the above emission factor.

4.8.14              The Yau Tong Bay area is by and large a built up area. To the immediate north Cha Kwo Ling Road is a housing development which is under construction. Further north to the north west of the Yau Tong Bay site is another committed major housing development of over 7,000 units at the existing Cha Kwo Ling Kaolin Mine, which is scheduled to be completed by 2010. Furthermore, further up to the north west to north east of the Yau Tong Bay site stand a number of major development namely Laguna City, Sceneway Garden, Ping Tin Estate, Kwong Tin Estate. To the east of the Yau Tong Bay site stand Yau Tong Estate and to the south east, an industrial area. For such an environmental setting, the “standard deviation of wind direction” has been taken to be 18° in the Tunnel Option in which the road networks are predominantly to the north-east to north-west of the development. The conservative approach of 12° applies for the Coastal Option.

4.8.15              Discrete Parcel Method (DPM) of CALINE4 has been used to compute NO2 concentrations in this assessment. It has assumed that the NO2 reactions take place with parcels. The reaction rates are assumed to be governed by the initial concentrations of NO, NO, and O3.  An O3 level of 63mg/m3, i.e. ~0.03ppm (taken from Air Quality 2000, Kwun Tong monitoring station, maximum daily hourly value) has been used. A typical result file is included in Appendix 4E.

Prediction of Vehicular Emissions from EHC Portal, Toll Plaza Road Section, Ventilation Exhaust Building, and Flaring Plant

4.8.16              Air quality impact due to emission from the tunnel portal and ventilation exhaust building of Eastern Harbour Crossing (EHC) Tunnel and the tunnel of Tseung Kwan O Western Coast Road has been predicted using the ISCST3 model.

4.8.17              Based on information provided by the Hong Kong Tunnel Company Limited, 70% of the tunnel emission was taken to be exhausted from the ventilation exhaust building. Portal emission impact on the ASRs were assessed based on the procedures given in Section III of Permanent International Association of Road Congresses (PIARC), 1991. The tunnel air jet along the axis of the tunnel was assumed to measure 200m from the portal. It was further assumed that only the well diluted parts would gradually become sheared off. By considering the air mass as volume sources and assume Gaussian dispersion, concentration of air pollutants at the ASRs due to portal emission were predicted.

4.8.18              Air emission from the Flaring Plant located at the restored Sai Tso Wan Landfill. Emission limit of NOx and Particulates and relevant operating parameters of the Flaring Plant were obtained from the Waste Facilities Business Unit of EPD and are summaried below:

Table 46     Pollutant Emission Limits & Operational Parameters of Sai Tso Wan Landfill Flare



Emission Limit of Nitrogen Oxides (NOx) (mg/m3)


Emission Limit of Particulates (taken as RSP) (mg/m3)


Flare Height (m)

6m above ground

Flare Internal Diameter (m)


Volume Flow Rate of Flue Gases (m3/hr) (assuming 50% CH4)


Stack Velocity (m/s)


Exit Temperature (°C) (taken as the combustion chamber temperature)


Modelled Emission Rate (g/s) of NOx


Modelled Emission Rate (g/s) of NO2


Modelled Emission Rate (g/s) of RSP



4.8.19              Figure 4.1 shows the location of the Sai Tso Wan Landfill flaring plant.

4.8.20              Worst case emission rates of NO2 and RSP from the portal were calculated based on the peak hour traffic flows within the tunnel. Appendix 4C presents a worksheet showing the calculation of pollutant emission rates from the tunnel portals, Toll Plaza Idling Vehicles, and Ventilation Exhaust Building.

4.8.21              Emissions from idling vehicles near the EHC toll plaza have been modelled as a series of line sources. The traffic on all lanes approaching (i.e. westbound lanes) or leaving (i.e. eastbound lanes) the portal tunnel at a distance of 100m from the toll was assumed to be “stationary”.  All vehicles are assumed to be free-flowing once they pass through the toll.  Emission rates of air pollutants from the idling vehicles were calculated based on the idling emission factors presented in Table 4.6.

4.8.22              A worksheet giving details on the calculation of pollutant emission from idling vehicles is presented in Appendix 4C. Sample calculations of emission rates are also included in Appendix 4C.

Table 4.7     Idling Emission Factors of Vehicles (g/min-veh)


Passenger Car

Light Goods Vehicle

Heavy Goods Vehicle












N.B. Emission rates of RSP were scaled from the NOx idling emission factors based on assuming the same RSP : NOx Ratio as for free flowing vehicles.

Figures showing the road links used in the modeling exercise and the sample calculations for emissions from open roads are provided in Appendix 4Ca.

Figure 4.1   Location of the Sai Tso Wan Landfill Flaring Plant

Noise Barriers

4.8.23              Since the final design of the tunnel of Tseung Kwan O Western Coast Road and the future extension of the Ko Fai Road is not confirmed at the time of the assessment.  Provision of noise barrier is not confirmed.  The worst case scenario is without any noise barrier, so that vehicular emission will be at road level, close to elevation of nearby roads. However, noise barriers were recommended in the noise chapter and hence for consistency, the assessment has taken into account the effect of the noise barriers.

4.8.24              Noise barrier effect of the proposed noise mitigation measures on the dispersion of vehicular emitted pollutants were taken into account in the vehicular emission impact calculation. Pollutants release height will be raised to the top of the barrier, and release location will be located at the edge of the barrier to assess the worst possible situation.

4.8.25              In order to reduce the traffic noise impact generated by Ko Fai Road and Cha Kwo Ling Road upon the development, purpose-built noise barriers along the site boundary are proposed as shown in Appendix 4D.

Vehicular Emission Dispersion Model

4.8.26              The vehicular emission impact from open roads at the ASRs were evaluated by computer model CALINE4 using the Discrete Parcel Method, which is an acceptable approach by EPD on the prediction of near field impacts of traffic emissions. Typical result files containing all the control parameters, input data and the calculated pollutants concentrations are enclosed in Appendix 4E for reference. Highest 24-hour level was obtained from the following equation:

24-hour highest concentration =    0.4 x highest 1-hour day time concentration

4.8.27              Emission from portal and ventilation shaft from the EHC and the tunnel of Tseung Kwan O Western Coast Road were evaluated with the ISCST3 model.  A typical ISCST output file containing the input data, such as the emission rate and emission location, is included in Appendix 4F for reference.


4.8.28              We have made the following assumptions regarding the tunnel of Tseung Kwan O Western Coast Road to facilitate the assessment (which can be found in Appendix 4C):

(i)         Alignment and mPDs of the road networks including the tunnel of Tseung Kwan O Western Coast Road;

(ii)       The dimensions of the tunnel of Tseung Kwan O Western Coast Road;

(iii)     The location of exhaust of the tunnel of Tseung Kwan O Western Coast Road;

(iv)     The dimensions of the exhaust of the tunnel of Tseung Kwan O Western Coast Road; and

(v)       Tunnel ventilation schedule of the tunnel of Tseung Kwan O Western Coast Road.


4.8.29              The predicted cumulative maximum hourly and daily NO2 concentrations at selected floors, i.e. ground floor, first floor and seventh floor (for the both Coastal and Tunnel Option for WCR), were presented graphically in Appendix 4G. In calculating the hourly NO2 emission from EHC and the tunnel of Tseung Kwan O Western Coast Road’s portal and ventilation shaft, the day-time peak traffic flow has been assumed to be from 8 to 12 a.m. and 4 to 8 p.m. The results obtained were added onto the open-road traffic emission impacts, the industrial emission impact and the background air quality to evaluate the cumulative air quality impact due to traffic emissions on the proposed development. The assessment results indicate that the predicted NO2 levels at all air sensitive receivers of the subject site are within the relevant AQOs requirements.

4.8.30              Contours showing the maximum daily RSP concentration at selected floors due to vehicular emission are included in Appendix 4G, with background concentration added. The assessment results indicate that the predicted RSP levels at all air sensitive receivers of the subject site are within the relevant AQOs requirements.

4.8.31              Results for NO2 and RSP levels differ for the 2 scenarios of Minimum and Full reclamation because the traffic data varies.  For such a reason, concentration contours are given for each of the 2 reclamation scenarios, both on the without I/R interface scenario. These are the worst case scenario containing the basic footprints of the MLP.


4.8.32              The cumulative air quality impact due to nearby industrial stack source, surrounding road traffics, portal and ventilation shaft emissions from the EHC and the tunnel of Tseung Kwan O Western Coast Road, as well as background concentrations have been quantitatively assessed.  Results of the assessment indicate that the predicted 1-hour SO2, 24-hour SO2, annual SO2, 1-hour NO2, 24-hour NO2, and 24-hour RSP level at all identified ASRs representing both the residential developments and school areas will comply with the AQO standards. By adopting the conservative approach of using emission factors for the year 2011 into the peak traffic forecast of the year 2030, it is envisaged that the HKAQO can be achieved at all times within the proposed development.

4.9                      Construction Phase Impact

Fugitive Dust Emission Source

4.9.1                 Air pollutants concerned at the construction phase include Total Suspended Particulate (TSP) and Respirable Suspended Particulate (RSP), which are results of particulate suspension by winds during the construction activities of the proposed development. Other air pollutants such as carbon monoxide, carbon dioxide, nitrogen dioxide and sulphur dioxide generated by powered mechanical equipment and vehicle exhaust on site are considered to be insignificant since only minute quantities will be produced. The contractor is required to follow the requirements of the Air Pollution Control (Construction Dust) Regulation and provide effective mitigation measures to meet the Air Quality Objectives at the site boundaries at all time during the construction phase of the proposed development. An audit and monitoring program during construction shall be initiated to ensure construction dust impact will be controlled to within the relevant standards as stipulated in Annex 4 of the Technical Memorandum.

4.9.2                 Dust emission can arise from the following construction activities:

·            Drilling of ground;

·            Excavation resulting in exposed ground vulnerable to air erosion;

·            Handling of excavated material & building material;

·            Concrete batching;

·            Earth moving and grading;

·            Wind effect on material stockpiling;

·            Vehicle movements on unpaved haul roads and over construction site; and

·            Loading and unloading of construction materials and excavated debris.

Mitigation Measures for Fugitive Dust Emission

4.9.3                 Fugitive dust emission arising from construction activities can be effectively suppressed by incorporating proper mitigation measures into work procedures through contractual clauses, good site management, and close enforcement of the resident engineers. With such practices, the emission of construction dust will be kept at a minimum level and most of them will be suppressed on-site and deposited within short distance of the source. Where feasible, potential dust emission sources should be located at maximum possible distances from sensitive receivers.

General Site Management

4.9.4                 Appropriate working methods should be devised and arranged to minimise dust emissions and to ensure any installed control system and/or measures are operated and/or implemented in accordance with their design merits. No free falling of construction debris should be allowed, which should be let down by hoist or enclosed tunnel to the ground.

4.9.5                 Frequent mist spraying should be applied on dusty areas. The frequency of spraying will depend upon local conditions such as rainfall, temperature, wind speed and humidity. The amount of mist spraying should be just enough to dampen the material without over-watering which could result in surface water runoff.

Vehicles and Unpaved Site Roads

4.9.6                 Dust emission from unpaved roads comes predominantly from travelling of vehicles. Areas with the site where there is a regular vehicle movements should have an approved hard surface. Speed controls at a upper limit of 8 km/hr should be imposed and their movements should be confined to designed roadways within the site. All dusty vehicle loads should have side and tail boards and should be covered by tarpaulin extending at least 300 mm over the edges of the side and tail boards. Wheel-wash troughs and hoses should be provided at exit points of the site.

Material Stockpiling and Handling

4.9.7                 The amount of stockpiling should be minimised where possible. Construction material or debris should be covered and stored inside enclosed areas. Other control measures such as enclosed or semi-enclosed windboard should be used, where applicable, to minimise dust emission. Watering is an effective dust control measure commonly employed in storage piles and handling operations.

Concrete Batching Plant

4.9.8                 If concrete batching is required at the site, the plant should be cleaned and watered regularly as a good practice. Cement and other fine grained materials delivered in bulk should be stored in enclosed silos fitted with high level alarm indicator. Dry mix batching should be carried out in an enclosed area with exhaust fitted with an appropriate fabric filter system.


4.9.9                 Potential air quality impacts arising from construction activities of the proposed development can be minimised by site management programme and appropriate mitigation measures. By adopting appropriate mitigation measures, it is believed that the dust impact can be minimised to acceptable levels.

4.10                   Environmental Monitoring and Audit (EM&A) Requirements

4.10.1              Monitoring and audit of the Total Suspended Particulates (TSP) levels shall be carried out by during construction phase of the development to ensure that any deteriorating air quality could be readily detected and timely action taken to rectify the situation.

4.10.2              1-hour and 24-hour TSP levels should be measured at representative air sensitive receivers to monitor the impacts of construction dust on air quality.  Details of the EM&A requirement is contained in Section 10 - Environmental Monitoring and Audit, of this EIA report.

4.11                   Odour Impact from Sewage Retention Tank


4.11.1              Sewage discharge from the proposed Yau Tong Bay Development will be connected to the existing Kwun Tong Sewage Treatment Plant. According to the existing loading of the Kwun Tong Sewage Plant and the estimated discharge rate from the development, the cumulative discharge  will exceed the sewage treatment plant’s capacity by the time of population uptake at the proposed development. Upgrading work of the sewage treatment plant is proposed and scheduled to be completed by the year 2009. Meanwhile, a temporary sewage retention tank will be built within the site for temporarily holding sewage generated from the development, for less than 6 hours, and pumped to the Kwun Tong Sewage Treatment Plant during non-peak hours.

Odour Emission Source

4.11.2              An underground and totally enclosed temporary retention tank with effective volume of 2,784m3 will be built at the site to serve the first 10 residential blocks of the development to be occupied prior to year 2008. The temporary sewage retention tank shall be decommissioned by the year 2009 after completion of the upgrading works for the Kwun Tong Sewage Treatment Plant. The location of the temporary sewage retention tank is shown in Figure 4.4.  Design drawings of the temporary sewage retention tank is included in Appendix 4H for reference.

4.11.3              The tanks and the connecting sewage pipes will be submerged in the ground and the only opening from the sewage retention system to the atmosphere is two manholes for grit removal from two skimmers.

4.11.4              On the other hand, the Kwun Tong Sewage Treatment Plant is at some 1,200m away from the proposed development and hence no odour impact from its operations is anticipated.

4.11.5              The “sewage treatment plant” as indicated in Figure 1 of Appendix 2A (EIA SB) is in fact a seawater pumping station.  As this is an enclosed process, no odour source was identified.

Assessment Criteria

4.11.6              A limit value of 5 odour units (based on an averaging time of 5 seconds), as stipulated in Annex 4 “Criteria for Evaluating Air Quality Impact and Hazard to Life” of the TM has been adopted throughout this assessment.

Air Sensitive Receivers

4.11.7              Air sensitive receivers (ASRs) were selected in accordance with a 30m by 30m grid covering the entire proposed development. The variation of odour concentration were predicted at the breathing zone on ground floor, i.e. 1.5m above ground floor slab.


4.11.8              An odour impact assessment was conducted using ISCST modelling to evaluate the odour impact upon the Yau Tong Bay development. 

Emission Source Strength

4.11.9              Due to the sub-surface and fully enclosed design of the sewage retention tanks and pumps, odour emitted directly from the retention tank and getting into the ambient environment is unlikely.  The only possible source of odour emission from the entire sewage retention system is through the maintenance opening of the tank system inside a fully enclosed structure to be built above the pumps.  The design of the structure is shown in Appendix 4H.  A mechanical ventilation at a minimum of 5 air exchange per hour shall be provided for a workplace as a health and safety measures for the maintenance staff.

4.11.10          In determination of odour strength, reference is made to the “Sha Tin Sewage Treatment Works, Stage III Extension - Environmental Impact Assessment Study[1]. In that report, odour emission rates were calculated based on (i) relationship between odour concentration and physical factors; and (ii) the volumetric emission flow rate versus ventilation rate. This approach is considered appropriate for the purpose of our assessment of odour emission from sewage holding facility with a ventilation requirement.  Detail of the calculation method is given in Annex B of the said report. The following equations were extracted from the said report for illustration purposes:

      DF = 1.6 x (T/10)4.9 x (ORP + 200)-0.59                                                     [Eq. 1]

      E = DF x A x (V/3600) x Cf                                                                       [Eq. 2]


DF       =       Odour concentration expressed as dilution factor, Oum-3

T          =       Temperature of sewage, Fehrenheit F

ORP    =       Oxidation-reduction potential of sewage, mV

E          =       Emission rate, OU s-1

A         =       Air volume of the emission source, m3

V         =       Ventilation rate, air changes per hour

Cf        =       Correction factor to adjust emission rates in the ratio of design ventilation rate to that used in the derivation of Eq.1 (for 5 air changes per hour, Cf = 0.52)

Parameters used for the assessment are as list below:

T          =       86F

ORP    =       200mV for fresh sewage (holding period <6 hours)

A         =       1.0m x surface area of tank (assume holding tank is similar to inlet works and feed channels), Surface area of the tank: 22x53 m2. The exposed area during maintenance would be the surface areas of the wet wells and the screen chamber. The surface areas of the wet wells are 4.75mx4.5m, and 3.75mx4.5m, while that of the screen chamber is 9mx2.5m. Hence the total exposed surface area is 51.75m2.

V         =       5 ACPH

Volume of Structure above retention tank:           420 m3


4.11.11          Basing on the above equations and parameters as adopted from the said report, an odour emission rate of 66.15 OU/s was obtained. The 5 ACPH ventilation requirement of the structure above this storage tank is only switched on during the 1 hour maintenance period. Odour emission, if any, is therefore only expected to be experienced for a short period of time.

Conversion to 5-second Odour Concentrations

4.11.12          Based on the odour assessment criteria, modelled maximum 1-hour odour concentration at the assessment points have to be converted to a 5-second period in order to allow for a comparison with the 5-second odour criteria.

4.11.13          As per section 3.5.45 of the EIA, an odour conversion factor of 27 (Stability Class C) was used to convert the hourly concentration to 5 second concentration in order for comparison with the odour criteria.

Meteorological Conditions

4.11.14          Meteorological data of Junk Bay Weather Station of the year 1998 obtained from the Hong Kong Observatory have been used in the modelling. Parameters used include:

·            Hourly wind direction;

·            Hourly wind speed with minimum assumed as 1m/s;

·            Hourly Pasquill stability class (A to F);

·            Hourly ambient air temperature (°K);

·            Morning and afternoon mixing heights (m); and

·            Total sky cover, and sky cover and ceiling height of the 1st - 4th layer.

Mitigation Measures

4.11.15          Activated carbon filter to the efficiency of 99% shall be installed at the exhaust of the ventilation of the structure above the sewage holding tanks. This efficiency is achievable by commercially available product but need to be maintained regularly. In determining the maintenance requirement, considerations were given to the low usage and the relatively damper air in an area near the coast. The carbon filters are recommended to be changed monthly to maintain the high de-odourising efficiency.

Assessment Results

4.11.16          Odour assessments using ISCST3 modelling were conducted and odour strength contours are plotted at 1.5m above ground level which is closest to the temporary sewage tank. As a school site is in the vicinity, ground floor has been chosen to present the odour contours. Selected section of the ISCST result file is included in Appendix 4I, which contains the input parameters for the assessment.  The contours are shown in Figure 4.4. The contours show the mitigated odour strength across the site at the breathing height on ground floor, which is the worst hit level.


4.11.17          It is concluded that the temporary sewage retention tank will unlikely be giving rise to significant odour impact due to its being underground, temporary, and low maintenance requirement. With the installed activated carbon filters as mitigation, residual odour impact upon the nearby air sensitive receivers is expected to be within acceptable levels.

4.12                   Overall Conclusion

4.12.1              An Air Quality Impact Assessment for the proposed development at the Yau Tong Bay Comprehensive Development Area has been completed. The assessment covers quantitative air quality impact assessments due to industrial and vehicular emissions.

4.12.2              Results of the industrial air quality impact assessment indicate that the air quality impact at the proposed development due to industrial emissions within 1km radius from the subject site is likely to be acceptable. The predicted highest 1-hour, 24-hour, and annual average SO2 levels at all levels of the air sensitive receivers within the proposed development are within the relevant Air Quality Objectives (AQOs).

4.12.3              For air quality impacts due to vehicular emissions, the cumulative impacts arising from road traffics, portal emissions and ventilation exhausts of the Eastern Harbour Crossing, as well as the background pollutant concentrations have been assessed. Results indicate that predicted 1-hour and 24-hour NO2, and 24-hours RSP levels complies with the relevant AQOs at all air sensitive receivers of the proposed development.

4.12.4              With the fully enclose sub-surface design of the temporary retention tank, maximum separation provided, and the implementation of mitigation measures, the temporary retention tank shall not impose unacceptable odour impact upon the nearby sensitive receiver.

4.12.5              With proper dust suppression measures to be carried out by the contractor and regular dust monitoring, no insurmountable construction dust impact upon sensitive receivers in the vicinity is anticipate.

4.12.6              Assessments on the I/R interface have indicated no adverse air quality impact is anticipated.

4.12.1              In conclusion, it is not envisaged that there is any insurmountable environmental impact existed the subject site. With the adopted of appropriate mitigation measures, the proposed development should achieve full compliance of all relevant statutory and non-statutory environmental standards.




Appendix 4A

Master Layout Plan of the Proposed Development – Full Reclamation


Figures Showing Sources of Emission in Yau Tong Bay

Appendix 4B

Typical ISCST Result File for

the Industrial Air Quality Impact Assessment

Appendix 4C

Calculation of Pollutant Emission Rates from the EHC

and the tunnel of Tseung Kwan O Western Coast Road Tunnel Portals,

Toll Plaza Idling Vehicles, and Ventilation Exhaust Building

Appendix 4Ca


Figures showing Road Links used in Modelling

and Sample Calculations for Emissions from Open Roads


Appendix 4D

Proposed Noise Mitigation at the Site Boundary

Appendix 4E

Typical Caline4 Results Files for the

Vehicular Emission Impact Assessment

Appendix 4F

Typical ISCST Result File for the EHC

and the tunnel of Tseung Kwan O Western Coast Road Portal,

Ventilation Shaft Emissions Impact Assessment

Appendix 4G


Contour of Predicted Cumulative Pollutant Concentration

at Selected Locations


Contour of Cumulative Hourly Average

Sulphur Dioxide Concentration

Contour of Cumulative Daily Average

Sulphur Dioxide Concentration

Contour of Cumulative Annual Average

Sulphur Dioxide Concentration


For Coastal Alignment Option

Contour of Cumulative Hourly Average

Nitrogen Dioxide Concentration

Contour of Cumulative Daily Average

Nitrogen Dioxide Concentration

Contour of Cumulative Daily Average

Respirable Suspended Particulates Concentration

For Tunnel Option Without Ko Fai Road Connection

Contour of Cumulative Hourly Average

Nitrogen Dioxide Concentration


Contour of Cumulative Daily Average

Nitrogen Dioxide Concentration

Contour of Cumulative Daily Average

Respirable Suspended Particulates Concentration

Appendix 4H

Design Drawings of the Temporary Sewage Retention Tank


Appendix 4I

Selected Section of a Typical ISCST Result File

for the Odour Impact Assessment



[1] Sha Tin Sewage Treatment Works, Stage III Extension - Environmental Impact Assessment Study, Drainage Services Department, EIA-022/1999