3 AIR QUALITY

3.1 Introduction

3.1.1 This section presents air quality impact assessment during construction and operation phases of the Project. Representative Air Sensitive Receivers (ASRs) and the potential air quality impact arising from the Project on these receivers have been identified and assessed. Appropriate mitigation measures are proposed if necessary.

3.2 Environmental Legislation, Policies, Plans, Standards and Criteria

3.2.1 The criteria for evaluating air quality impacts and the guidelines for air quality assessment are set out in Annex 4 and Annex 12 of the Technical Memorandum on Environmental Impact Assessment Process (EIAO-TM).

Air Quality Objective & EIAO-TM

3.2.2 The Air Pollution Control Ordinance (APCO) provides the statutory authority for controlling air pollutants from a variety of sources. The Hong Kong Air Quality Objectives (AQOs), which must be satisfied, stipulate the maximum allowable concentrations over specific periods for typical pollutants. The relevant AQOs are listed in Table 3.1.

Table 3.1 Hong Kong Air Quality Objectives

Pollutant	Maximum Concentration (µg m^-3) ^(1)
	Averaging Time
	1 hour ^(2)	8 hour ^(3)	24 hour ^(3)	Annual ^(4)
Total Suspended Particulates (TSP)	^-	-	260	80
Respirable Suspended Particulates (RSP) ^(5)	-	-	180	55
Sulphur Dioxide (SO2)	800	-	350	80
Nitrogen Dioxide (NO2)	300	-	150	80
Carbon Monoxide (CO)	30,000	10,000	-	-
Photochemical Oxidants (as Ozone, O3) ^(6)	240	-	-	-

Notes:

(1) Measured at 298 K and 101.325 kPa.

(2) Not to be exceeded more than three times per year.

(3) Not to be exceeded more than once per year.

(4) Arithmetic mean.

(5) Suspended particulates in air with a nominal aerodynamic diameter of 10 mm or smaller.

(6) Photochemical oxidants are determined by measurement of ozone only.

3.2.3 The EIAO-TM stipulates that the hourly TSP level should not exceed 500 mgm^-3 (measured at 25°C and one atmosphere) for construction dust impact assessment. Standard mitigation measures for construction sites are specified in the Air Pollution Control (Construction Dust) Regulations.

Air Pollution Control (Construction Dust) Regulation

3.2.4 Notifiable and regulatory works are under the control of the Air Pollution Control (Construction Dust) Regulation. Notifiable works are site formation, reclamation, demolition, foundation and superstructure construction for buildings and road construction. Regulatory works are building renovation, road opening and resurfacing slope stabilisation, and other activities including stockpiling, dusty material handling, excavation, concrete production etc. This Project is expected to include both notifiable and regulatory works. Contractors and site agents are required to inform the Environmental Protection Department (EPD) on carrying out construction works and to adopt dust reduction measures to reduce dust emission to the acceptable level.

3.3 Description of the Environment

3.3.1 The air quality at the Study Area is primary affected by traffic emissions from the existing Tuen Mun Road, Castle Peak Road and local access roads. No major industrial premise is observed in the vicinity of the Project site.

3.3.2 The Project area is in Tuen Mun. The nearest EPD air monitoring station is in Yuen Long. According to EPD’s “Guideline on Assessing the ‘TOTAL’ Air Quality Impacts”, the latest five years average monitoring data should be adopted as the background concentration. Table 3.2 summarizes the annual average concentrations of the pollutants (NO₂, RSP and O₃) adopted as background concentrations for this air impact assessment.

Table 3.2 Annual Average Concentrations of Pollutants in the Latest Five Years (Year 2002 - 2006) at Yuen Long Air Quality Monitoring Station

Pollutant	Annual Average Concentration in the Latest Five Years (mg m^-3)
NO2	60
RSP	62
O3	32

3.4 Air Quality Sensitive Receivers

3.4.1 In accordance with the Annex 12 of the EIAO-TM, any domestic premises, hotel, hostel, hospital, clinic, nursery, school, educational institution, office, factory, shop, shopping centre, place of public worship, library, court of law, sports stadium or performing arts centre are considered to be an ASR. Any other place with which, in terms of duration or number of people affected, has a similar sensitivity to the air pollutants as the aforelisted places are also be considered to be a sensitive receiver, for example, playground, sitting area of parks/promenade.

3.4.2 No planned ASRs are located in vicinity of the Project. The identified representative ASRs are listed in Table 3.3 and the corresponding locations are shown in Figures 3.1.

Table 3.3 Details of Representative Air Sensitive Receivers

ASR	Description	Use	Distance from project boundary (m)
A1	Tuen Mun Hospital	Hospital	122
A2	Block F, Tuen Mun Hospital	Residential	118
A3	Block A, Brilliant Garden	Residential	56
A4	SKH Mung Yan Primary School	School	113
A5	Kwong Choi Market	Market	22
A6	Lakeshore Building	Residential	20
A7	The Church of Christ in China Tam Kee Lai Fun Memorial Secondary School	Education Institution	3
A8	Kam Fat Building	Residential	30

3.4.3 Several elevations have been chosen for the assessment: 1.5 metres above local ground level (which is the average height of the human breathing zone), 5.0 metres and 10.0 metres above local ground level.

3.5 Identification, Prediction and Evaluation of Environmental Impacts

Construction Phase

3.5.1 The construction period for the Project would be from early 2008 to end 2009. The major construction activities for the Project including:

- Excavation;

- Road works;

- Slope works;

- Foundation works for noise barriers;

- Installation of noise barrier supporting frame; and

- Installation of noise barrier panel; and

- Installation of high mast lighting.

3.5.2 Potential air quality impacts arising from the construction of the Project would mainly be related to dust nuisance from excavation, material handling and wind erosion of the site. In view of site constraint, the section length of road to be widened would be about 50m at a time. One dump truck would be allowable on site for unloading materials due to limited work area. Therefore, no adverse dust impact would be expected at the nearby ASRs. During the construction period, although the road improvement works at Tuen Mun Town Centre would overlap with the Project by a number of months, it is located 500m away from the work area of the Project and hence cumulative dust impact would not be expected.

3.5.3 With the adoption of dust suppression measures stipulated in Air Pollution Control (construction Dust) Regulation and good site practices, adverse construction dust impacts would not be expected.

Operation Phase

3.5.4 Potential air quality impact on the surrounding ASRs during the operation phase of the Project includes:

- background pollution levels based on five years averaged monitoring data from EPD monitoring station at Yuen Long which summarised in Table 3.2; and

- open road emissions from the existing roads and widened Tuen Mun Road at Tsing Tin Interchange with the incorporation of the proposed noise barriers.

3.5.5 According to the emission derived from EMFAC-HK Model, the ratio of total NO₂, RSP and CO emissions to the corresponding 24-hour average AQO (there was no 24-hour average AQO for CO, the AQO of CO for shorter period of 8-hour CO is used) was 0.0072, 0.0032 and 0.0015 respectively. Besides, the ratio of total NO₂ and CO emissions to the corresponding 1-hour average AQO was 0.0036 and 0.0005 respectively. This indicated that NO₂ and RSP are the most critical air pollutants of road traffic emission. In other words, if the predicted NO₂ and RSP concentrations complied with the corresponding AQO, air pollutants like CO with lower ratio would also comply with their respective AQO. NO₂ and RSP were therefore selected as the most critical air pollutants for the purpose of this assessment.

3.6 Assessment Methodology

Construction Phase

3.6.1 As mentioned in Section 3.5.3, insignificant dust impact would be expected during construction phase of the Project, therefore, only qualitative assessment would be undertaken in the study.

Operation Phase

3.6.2 The EPD recommended air dispersion model, CALINE4, was employed to predict the vehicle exhaust pollutants from the Project and surrounding road network. All major roads within 500m of the study area were included in the model. The hourly average NO₂, daily average NO₂ and RSP were calculated in the model.

3.6.3 According to the construction programme, the completion of the Project would be in Year 2009. The predicted morning peak traffic flows for year 2024, which are the highest emission strength from the road within next 15 years after the operation of the Project. However, for representing the worst-case air quality scenario, predicted morning and afternoon peak traffic flows for Year 2024 were used for estimating the vehicular impacts during daytime and night-time, respectively. The projected 2024 morning and afternoon peak hour traffic flows and vehicle compositions were attached in Appendix 3.1.

Fleet Average Emission Factors

Vehicle Classes

3.6.4 EMFAC-HK model was adopted to estimate the vehicle emission rates and inventories of exhaust, carbon monoxide, oxides of nitrogen and particulate matter.

3.6.5 The “vehicle fleet” refers to all motor vehicles operating on roads within this Study Area. The modelled fleet was broken down into 16 vehicle classes based on the information as shown on Table 4.4 (Registration and Licensing of Vehicle by Fuel Type) of the Transport Monthly Digest (Mar 2007) and vehicle population provided by EPD. The vehicle group classification was based on the definition in The Annual Traffic Census 2005 – Appendix F Vehicle Classification System.

3.6.6 Referring to Transport Monthly Digest (Mar 2007), there were only 0.5% of private car using diesel fuel. It was therefore assumed that all private cars would be grouped as “petrol private car” in the model in view of negligible value. The Transport Monthly Digest (Mar 2007) also indicated that there were 3% light good vehicle using petrol fuel. As a conservative approach, all light good vehicles would be grouped as “diesel light good vehicle”. The 16 vehicle classes which were modelled in EMFAC-HK are summarized in Table 3.4.

Table 3.4 Vehicle Classes in EMFAC-HK Model

Vehicle Class	Description	Fuel Type	Gross Vehicle Weight
MC1	Petrol Private Cars (PC) & Light Goods Vehicles (LGV)	Petrol	all
MC3	Diesel Private Cars & Light Goods Vehicles<2.5t	Diesel	<=2.5t
MC4	Diesel Private Cars & Light Goods Vehicles 2.5-3.5t	Diesel	>2.5-3.5t
MC5	Public Light Buses	LPG, Diesel	all
MC6	Light Goods Vehicles >3.5t	Diesel	>3.5-5.5t
MC7	Medium & Heavy Goods Vehicles with GVW 5.5-15t	Diesel	>5.5-15t
MC8	Medium & Heavy Goods Vehicles with GVW >=15t	Diesel	>15t
MC10	Double Deck Franchised Buses	Diesel	all
MC11	Motor Cycles	Petrol	all
Taxi3	Taxi	LPG	all
Taxi4	Private Light Buses <3.5t	LPG, Diesel	<=3.5t
Taxi5	Private Light Buses >3.5t	LPG, Diesel	>3.5t
Taxi6	Non- franchised Buses <6.4t	Diesel	<=6.4t
Taxi7	Non- franchised Buses 6.4-15t	Diesel	>6.4-15t
Taxi8	Non- franchised Buses >15t	Diesel	>15t
Taxi10	Single Deck Franchised Buses	Diesel	all

Road Grouping

3.6.7 With reference to the road design, the speed limit of Tuen Mun Road and other local road were 70kph and 50kph, respectively. Hence, two sets of emission factors for the two road types were calculated. Details of the classification of road type are presented in Appendix 3.2.

Input Assumption in EMFAC-HK

3.6.8 The latest model version EMFAC-HK v1.2 provided by EPD was employed in this Study. The input parameters and model assumptions made in EMFAC-HK model are summarized as follows.

Modelling Modes

3.6.9 As suggested in EPD guideline, “Burden mode” which can provide hourly vehicular emissions according to the diurnal variations of traffic flow, temperature, relative humidity and speed, was selected for this Project. Both CVs and MVE17G CVS output file formats were produced.

Technology Fractions

Exhaust Technology Fractions

3.6.10 Each vehicle class had diverse technological factors in different years. According to the underlying assumption in EMFAC-HK, each vehicle class could be modelled by the individual behaviour of unique technology groups. Each technology group represented the same vehicle class had distinct emission control technologies, similar in-use deterioration rates and responded the same to repair. It means that the vehicles from the same class had the same emission standards or specific equipment installed on them (e.g. multi-port fuel injection, three-way catalyst, adaptive fuel controls, etc) which made them had the same performance.

3.6.11 The Up to Date Vehicle Licensed Number by Age and Technology Group Fractions provided in EPD’s website was adopted in this assessment. Since the provided exhaust technology fractions were only up to Year 2003, for those after Year 2003 were projected in accordance with EPD Guideline on Modelling Vehicle Emissions Appendix II “The Implementation Schedule of Vehicle Emission Standards in Hong Kong (Updated as at 17 August 2005)” and Appendix III “The Technology Group Indexes”.

3.6.12 However, no sufficient information was available for the projection of petrol private cars & light goods vehicles, diesel private cars & light goods vehicles and private light buses > 3.5t, some adjustments were made.

3.6.13 According to the EPD Guideline on Modelling Vehicle Emissions, it mentioned that the existing vehicle emission control programmes were included in the EMFAC-HK. No other vehicle emission control measures were assumed in the assessment, thus the projected breakdown (%) in Years 2004 – 2024 of private cars & light goods vehicles and breakdown (%) of diesel & LPG private light bus >3.5t were made reference to the default data.

3.6.14 An addition adjustment on the projection of single deck franchised bus (FBSD) was made. In accordance with EPD Guideline on Modelling Vehicle Emissions Appendix II, Implementation Schedule of Vehicle Emission Standards in Hong Kong (Updated as at 17 August 2005), the emission standard of diesel franchised buses were upgraded to Euro III since 1 October 2001. However, in accordance with the updated exhaust technology fractions provided by EPD, FBSD was not upgraded to EURO III in Year 2001. Thus, as a conservative approach, the emission standards of FBSD in Year 2001-2005 was assumed as Euro II and the emission standards of FBSD after Year 2005 would follow the Implementation Schedule of Vehicle Emission Standards in Hong Kong. The adjusted exhaust technology fractions are presented in Appendix 3.3.

Evaporative Technology Fractions

3.6.15 Evaporative technology fraction in the model was based on the default value.

Vehicle Population

3.6.16 As recommended in the EPD Guideline on Modelling Vehicle Emissions, the latest vehicle age distribution data provided in the EPD’s website, that is, the Vehicle Population in Year 2003, was used except the population of private car and taxi.

3.6.17 After the implementation of stringent emission standard in 1998, there was no new certification of diesel private car registration in Hong Kong. Thus, the number of diesel private car was extracted and grouped into the “petrol private car”. Since diesel Taxi started to switch to LPG from Year 2001 and only one fuel type of Taxi was available in EMFAC-HK Model, 100% LPG taxi was therefore be assumed in this assessment.

3.6.18 Environment, Transport and Works Bureau (ETWB) implemented an incentive scheme to encourage the early replacement of diesel light buses with LPG or electric ones since 2002. In view of the environmental report established by EPD, nearly 80% of new public light buses in 2004 operating on LPG. As a conservative approach, the incentive scheme for light buses would not be considered in this assessment as a conservative approach.

3.6.19 According to the above assumptions, vehicle population in Year 2009 was calculated and is presented in Appendix 3.4.

Accrual Rate

3.6.20 The default accrual rates in EMFAC-HK were estimated from the local mileage data adjusted to reflect the total vehicle-mile-travelled (VMT) for each vehicle class. The default value was used.

Diurnal Variation of Daily Trips and Daily Vehicle-Mile-Travelled (VMT)

Diurnal Variation of Daily Trips

3.6.21 The diurnal variation of daily trips was used to estimate the start emissions of petrol vehicles, thus the trips of other vehicles would be zero. The number of trips per day of petrol vehicle was equal to the number of cold starts per day. There would not be cold start at the middle of Tuen Mun Road, thus, zero vehicle trip per day was assumed for Tuen Mun Road. For other roads, the diurnal variation of daily trips could be estimated based on the ratio of trip/VMT in the entire territory and the Study Area. For other roads, the number of vehicle trips was calculated by the following equation:

Vehicle Trip of Class 1 in the Study Area at hour 1 = VMT for vehicle class 1 in the Study Area at hour 1 ´ Vehicle trip of Class 1 in the territory*/VMT for vehicle class 1 in the territory*

* where the trip and VMT in the territory could be read from the default data of EMFAC-HK model

Diurnal Variation of Daily Vehicle Mile-Travelled (VMT)

3.6.22 Vehicle-mile-travelled (VMT) represents the total distance travelled on a weekday. The VMT was calculated by multiplying the number of vehicle which based on the forecast hourly traffic flow in Year 2024 and the length of road travelled in the Study Area. The input in the model was by vehicle/fuel/hour.

3.6.23 The hourly profile of traffic flow was made reference to the Annual Traffic Census 2005. The major core station along Tuen Mun Road (No. 5001) was selected for representing the hourly profile of all roads within the Study Area. However, the same traffic breakdown in % would be applied to all hours.

3.6.24 Those assumptions of producing the hourly traffic flow and the traffic breakdown were approved by Transport Department. The adopted daily trips and VMT are summarized in Appendix 3.5.

Hourly Temperature and Relative Humidity Profile

3.6.25 According to the information provided by Hong Kong Observatory (HKO), Tuen Mun meteorological station was the nearest station of the Project and was adopted for the model input.

Speed Fraction

3.6.26 The speed limits of each road were made reference to the Traffic AIDs from Transport Department. Referring to the Traffic AIDs, the speed limits of all road links within the Study Area (except Tuen Mun Road) would be 50kph, whereas the speed limit of Tuen Mun Road would be 70kph. It was assumed that all vehicle classes had the same speed profile in the model.

3.6.27 To simulate the effect of different road speed during the rush and non-rush hour, sensitivity test had been done. The design road speed limits were assumed for representing the situation during non-rush hour; while the vehicle speed of peak hour flow in Year 2024 would be representing the situation during rush-hour.

3.6.28 The flow speeds were calculated based on the peak traffic flow in Year 2024 and volume/capacity ratio of different road type. For obtaining the speed fractions of each vehicle type, the vehicle speeds of each road link were first calculated and weighing by VMT. If the road links are in two-way direction, the vehicle speeds were calculated by weighing vehicle speeds of each direction.

3.6.29 In the model, same road speeds were applied to all hours to demonstrate the effect of using peak flow speed and design speed. Based on the comparison of the total daily emission rate, the worst road speed fraction was applied for predicting the vehicle emissions. Model year of 2024 was adopted in the sensitivity test.

3.6.30 From the results of the sensitivity test, it indicated that higher total daily NO_X and RSP emissions would be obtained at lower road speed, only the total daily NO_X emissions of trunk roads under design speed fractions were slightly greater than that under peak hour flow speed fractions. However, the dominant NO_X emissions were obtained on other roads under all scenarios. Thus, the peak hour flow speed in Year 2024 was applied to all hours for predicting the total hourly emissions in this assessment as a conservative approach. The sensitivity results are presented in Appendix 3.6.

Model Year

3.6.31 For the purpose of finding the worst emission year, 15 sets vehicle emissions based on the emission control schemes from Year 2009 to 2024 by using the same VMT in 2024 were produced. The emission standards of each vehicle class were the major factor influencing the vehicle exhaust emission. According to the implementation schedule of emission standards, the latest program was up to Year 2006 or 2009. Better emission controlled vehicles (Euro IV and V) would be replaced the old pre-Euro diesel/petrol vehicles. The vehicle exhaust emissions of Year 2009 to Year 2024 were calculated. Sensitivity tests were undertaken to calculate the vehicle exhaust emissions in different year by using the VMT of each road category and the flow speed fractions in Year 2024. By using the peak hour flow speed in Year 2024 at all hours, the total daily NO_X an RSP emissions by 16 vehicle classes in different vehicle exhaust emission year from 2009 to 2024 are summarized in Appendix 3.7.

3.6.32 Comparing the total daily NO_X and RSP emissions under different vehicle exhaust emission years from Year 2009 to 2024, the highest vehicle emissions were found in Year 2009 using emission control scenario and were decreased from Year 2009 to 2024. Therefore, as a conservative approach, the emissions using emission control scenario in Year 2009 were adopted for this Project.

3.6.33 As a conservative approach, the hourly emissions in Year 2009 were first divided by the number of vehicles and the distance travelled to obtain the emission factors in gram per miles per vehicle. The calculated maximum vehicle emission factors were then selected for incorporation into the air dispersion model. These conservative vehicle emission factors together with the forecasted Year 2024 peak traffic flow were adopted in the air quality impact assessment for this Project. The calculation of fleet vehicle emission for is presented in Appendix 3.8.

3.6.34 The calculated vehicular emissions for different vehicle categories were listed in Table 3.5.

Table 3.5 Emission Factors for Year 2009 for Different Vehicle Classes (EMFAC-HK)

Vehicle Class	Description	Emission Factors for 2009, g/mile-veh
		NOX		RSP
		Trunk Road	Other Road	Trunk Road	Other Road
MC1	Petrol Private Cars (PC) & Light Goods Vehicles (LGV)	0.2272	0.2818	0.0053	0.0083
MC3	Diesel Private Cars & Light Goods Vehicles<2.5t	0.9498	1.0722	0.3164	0.4021
MC4	Diesel Private Cars & Light Goods Vehicles 2.5-3.5t	0.5317	0.5866	0.1633	0.2095
MC5	Public Light Buses	0.7523	0.7675	0.6154	0.6869
MC6	Light Goods Vehicles >3.5t	3.4661	3.7633	0.3939	0.4999
MC7	Medium & Heavy Goods Vehicles with GVW 5.5-15t	7.3436	7.8873	0.7244	0.8988
MC8	Medium & Heavy Goods Vehicles with GVW >=15t	9.2875	10.0082	0.7963	1.0268
MC10	Double Deck Franchised Buses	5.1323	5.8073	0.2475	0.3305
MC11	Motor Cycles	1.0231	1.1372	0.0400	0.0625
Taxi3	Taxi	0.2514	0.2819	0.0233	0.0328
Taxi4	Private Light Buses <3.5t	0.0000	0.0000	0.0000	0.0000
Taxi5	Private Light Buses >3.5t	0.7471	0.8242	0.4687	0.6083
Taxi6	Non- franchised Buses <6.4t	0.0000	0.0000	0.0000	0.0000
Taxi7	Non- franchised Buses 6.4-15t	6.4663	7.0735	0.5716	0.7392
Taxi8	Non- franchised Buses >15t	0.0000	0.0000	0.0000	0.0000
Taxi10	Single Deck Franchised Buses	0.0000	5.4401	0.0000	0.8151

Note: - Since there is no non-franchised buses <6.4t, non-franchised buses >15t travelled within the study area and no single deck franchised travelled at trunk road within the study area, the calculated emission factors for these vehicle classes are zero.

Model Assumptions for Open Road Vehicle Emission

3.6.35 As mentioned in section 3.6.2, CALINE4 dispersion model was used for calculation of the hourly NO₂, 24-hour NO₂ and 24-hour RSP concentrations. The following summarises the meteorological conditions adopted in the air quality modelling using the CALINE4 model:

- Wind speed : 1 m/s

- Wind direction : worst case wind directions

- Wind variability : 18° (D Class) / 6° (F Class)

- Stability class : D (Daytime) / F (Night-time)

- Surface roughness : 1 m

- Mixing height : 500 m

3.6.36 The CALINE4 model calculates hourly concentrations only. The highest predicted hourly concentration between daytime and evening time was assumed to be maximum 1-hour average concentration. With reference to the Screening Procedures for Estimating the Air Quality Impact of Stationary Source (EPA-454/R-92-019), a conversion factor of 0.4 is used to convert the 1-hour average concentrations to 24-hour average concentrations.

3.6.37 Secondary air quality impacts arising from the implementation of roadside noise barriers were also incorporated into the air quality model. For the proposed cantilever noise barriers along the Tuen Mun Road Tsing Tin Interchange (as shown in Figure 4.2), it was assumed that dispersion of the traffic pollutants would have effect similar to assuming that traffic pollutants would be emitted from the top of the canopies at a point close to the central divider of the road. The calculation of open road emissions is presented in Appendix 3.9.

NO₂/NO_X Emissions Conversion

3.6.38 The NO₂/NO_X conversion for all vehicle emission sources for all averaging periods was estimated based on the Ozone Limiting Method. The latest five years (2002 – 2006) annual average of daily hourly maximum ozone concentrations recorded at EPD’s Yuen Long Air Quality Monitoring Station of 74µg/m³ was adopted for the calculation. The NO₂/NO_X conversion was calculated as follows:

[NO₂]_pred = 0.1 ´ [NO_X]_pred + MIN {0.9 ´ [NO_X]_pred, or (46/48) ´ [O3]_bkgd}

where

[NO₂]_pred is the predicted NO₂ concentration

[NO_X]_pred is the predicted NO_X concentration

MIN means the minimum of the two values within the brackets

[O3]_bkgd is the representative O₃ background concentration

(46/48) is the molecular weight of NO₂ divided by the molecular weight of O₃

Concentration Calculation

3.6.39 The cumulative hourly average NO₂, daily average NO₂, and RSP concentrations are predicted at the discrete receivers taking into account of the background air quality (as presented in Table 3.2) and the vehicle emissions (as presented in Table 3.5).

3.7 Prediction and Evaluation of Environmental Impacts

Construction Phase

3.7.1 Due to limited work areas, adverse dust impact at the ASRs would not be expected from the land-based construction. No unacceptable dust impact would be expected after proper implementation of dust control and suppression measures stipulated in the Air Pollution Control (Construction Dust) Regulation.

Operation Phase

3.7.2 Taking into account vehicle emissions from open road networks and the background pollutant concentrations, the predicted 1-hour average NO₂, 24-hour average NO₂ and 24-hour average RSP concentrations were predicted and the highest pollutant concentrations at each ASR under the worst wind directions were calculated. Table 3.6 summarized the predicted maximum 1-hour average NO₂, 24-hour average NO₂ and 24-hour average RSP concentrations at different elevations.

Table 3.6 Predicted Maximum 1-hour Average NO2, 24-hour Average NO2 and RSP Concentrations the Representative Air Sensitive Receivers

ASR	Assessment Height (mAG)	Predicted 1-hour Averaged NO2 Concentration (mg/m^3)	Predicted 24-hour Averaged NO2 Concentration (mg/m^3)	Predicted 24-hour Averaged RSP Concentration (mg/m^3)
A1	1.5	168	103	78
	5	167	103	77
	10	164	101	76
A2	1.5	165	102	76
	5	164	101	75
	10	159	100	74
A3	1.5	186	110	84
	5	185	110	83
	10	183	109	83
A4	1.5	162	101	75
	5	160	100	74
	10	158	99	73
A5	1.5	196	115	89
	5	194	113	87
	10	187	111	85
A6	1.5	191	112	88
	5	190	112	85
	10	187	111	84
A7	1.5	262	141	113
	5	249	135	108
	10	231	128	101
A8	1.5	188	111	83
	5	188	111	84
	10	177	107	80

Note: Background concentrations are included.

3.7.3 Based on the above prediction, no exceedance of 1-hour average NO₂, 24-hour average NO₂ and 24-hour average RSP objective would occur at any representative ASR in the Study Area. From the results, it is found that the maximum pollutant concentrations would occur at 1.5m above ground (the lowest assessment level). The predicted maximum hourly average NO₂, 24-hour average NO₂ and 24-hour average RSP concentration contours at 1.5m above local ground are shown in Figures 3.2 to 3.4.

3.8 Mitigation of Adverse Environmental Impacts

Construction Phase

3.8.1 To ensure compliance with the relevant standards, dust mitigation measures stipulated in the Air Pollution Control (Construction Dust) Regulation and good site practices should be incorporated in the contract document to control potential dust emission from the site. The major dust suppression measures include:

- skip hoist for material transport should be totally enclosed by impervious sheeting;

- every vehicle should be washed to remove any dusty materials from its body and wheels before leaving a construction site;

- the area where vehicle washing takes place and the section of the road between the washing facilities and the exit point should be paved with concrete, bituminous materials or hardcores;

- where a site boundary adjoins a road, streets or other accessible to the public, hording of not less than 2.4m high from ground level should be provided along the entire length except for a site entrance or exit;

- every stack of more than 20 bags of cement should be covered entirely by impervious sheeting places in an area sheltered on the top and the 3 sides;

- all dusty materials should be sprayed with water prior to any loading, unloading or transfer operation so as to maintain the dusty materials wet;

- the height from which excavated materials are dropped should be controlled to a minimum practical height to limit fugitive dust generation from unloading;

- the load of dusty materials carried by vehicle leaving a construction site should be covered entirely by clean impervious sheeting to ensure dust materials do not leak from the vehicle; and

- instigation of an environmental monitoring and auditing program to monitor the construction process in order to enforce controls and modify method of work if dusty conditions arise.

Operation Phase

3.8.2 The predicted air quality impacts on the ASRs would comply with the AQO. No mitigation measures would be required during operation phase.

3.9 Evaluation of Residual Impacts

Construction Phase

3.9.1 With the implementation of dust suppression measures stipulated in Air Pollution Control (Construction Dust) Regulation during construction, no adverse residual dust impact would be expected.

Operation Phase

3.9.2 No adverse residual traffic emission impact would be predicted.

3.10 Environmental Monitoring and Audit

Construction Phase

3.10.1 With the implementation of the proposed dust suppression measures, good site practices and dust monitoring and audit programme, acceptable dust impact would be expected at the ASRs. Details of the monitoring requirements such as monitoring locations, frequency of baseline and impact monitoring are presented in the stand-alone EM&A Manual.

Operation Phase

3.10.2 Since the predicted air quality in the study area would comply with the AQO, no environmental monitoring and audit is proposed.

3.11 Conclusion

Construction Phase

3.11.1 In view of limited scale of construction area, adverse dust impact at the ASRs would not be expected from the Project. Nevertheless, appropriate dust control and suppression measures as stipulated in the Air Pollution Control (Construction Dust) Regulation should be implemented to minimize any potential dust impact.

Operation Phase

3.11.2 The potential impacts arising from the background pollutant levels within and adjacent to the Project site, vehicle emissions from open road networks and the implementation of roadside noise barriers were assessed. Results showed that the predicted air quality at the ASRs would comply with the AQOs. No mitigation measures are proposed.