3      aIR qUALITY

3.1       Introduction

3.2       Environmental Legislation, Policies, Plans, Standards and Criteria

3.3       Description of the Environment

3.4       Sensitive Receivers

3.5       Identification of Environmental Impacts

3.6       Mitigation of Adverse Environmental Impacts

3.7       Evaluation of Residual Impacts

3.8       Environmental Monitoring and Audit

3.9       Conclusion




3                    aIR qUALITY

3.1              Introduction

3.1.1          This section presents an air quality impact assessment during the dredging for the cross-harbour water mains from Wan Chai to Tsim Sha Tsui (DP6) of the Wan Chai Development Phase II project.  In view of the project nature, no adverse air quality impact during the operation phase would be anticipated.  Thus, this section would only focus on construction air quality impact assessment.

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 of certain pollutants over specific periods.  The relevant AQOs are listed in Table 3.1.

Table 3.1     Hong Kong Air Quality Objectives


(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 25oC and one atmosphere) for construction dust impact assessment.  Standard mitigation measures for construction sites are specified in the Air Pollution Control (Construction Dust) Regulations.

3.2.4          In accordance with the EIAO-TM, odour level at an air sensitive receiver should meet 5 odour units based on an averaging time of 5 seconds for odour prediction assessment.

3.3              Description of the Environment

Baseline Conditions

3.3.1          The dredging area for proposed cross-harbour water mains is between Wan Chai and Tsim Sha Tsui, the study area is in Victor Harbour.  The nearest EPD air quality monitoring stations are in Central and Central/Western.  The annual average concentrations of the pollutants measured at EPD’s Central / Western and Central air quality monitoring stations in 2006 adjacent to the WDII development area are summarised in Table 3.2.

Table 3.2     Annual Average Concentrations of Pollutants in 2006


Annual Average Concentration in 2006 (mg m-3)

Monitoring Stations






Central / Western



Central / Western



Central / Western


3.4              Sensitive Receivers

3.4.1          The study area is within 500m from the project boundary.  The study area of air quality assessment is shown in Figure 3.1.  The Air Sensitive Receivers (ASRs) including domestic premises, commercial buildings, educational institutions, and recreational and leisure facilities have been identified for air quality impact assessment.

3.4.2          The identified nearest ASRs to the work site of DP6 are Hong Kong Convention & Exhibition Centre Extension in Wah Chai and Art Centre in Tsim Sha Tsui.

3.5              Identification of Environmental Impacts

3.5.1          The dredging activities would be commenced in January 2009.  One dredger would be used and the duration would be last for 16 days.  As dredging is marine based activity, dust nuisance from this construction activity is not anticipated.   

3.5.2          Insignificant marine traffic emission impact from the dredger is expected as only one dredger to be operated at the work site.  Under normal operation, equipment with proper maintenance is unlikely to cause significant dark smoke emissions and gaseous emissions are expected to be minor. Thus, the AQOs are not expected to be exceeded.  Notwithstanding, plant should be regularly maintained to minimise emissions. 

3.5.3          In accordance with the construction programme, there is no other construction activity to be operated concurrently within 500m study area of DP6, no cumulative air quality impact is anticipated.

3.5.4          The dredging area is not a stagnant or low water flow area in Victoria Harbour.  The sediment is not expected to be highly contaminated.  Hence, generation of adverse odour impact from dredging is not anticipated.


3.6              Mitigation of Adverse Environmental Impacts

3.6.1          No adverse air quality impacts at the ASRs are expected during dredging.  However, the operated dredger should be regularly maintained to minimise emissions. 


3.7              Evaluation of Residual Impacts

3.7.1          No adverse residual air quality impact arsing from the DP6 would be expected.

3.8              Environmental Monitoring and Audit

3.8.1          No adverse air quality impact would be expected arsing from the DP6, air quality monitoring and audit is considered unnecessary. 

3.9              Conclusion

3.9.1          Negligible dust impact and emission impact from the DP6 would be expected at the nearest ASRs.  Air quality monitoring and audit is therefore not required.