EIA Reports Related to HZMB
Supplementary Information on Consideration and
Assessment of Ozone in EIAs
1. Introduction
In the operation phase air quality impact assessment under the EIA Reports for HKLR & HKBCF and TMCLKL, the key pollutants from road emissions have been identified as NO2 and RSP. The concentrations of these pollutants have been predicted for the assessment year at 2031 and have been assessed accordingly. The EIA Reports have stated that since O3 is not a pollutant directly emitted from vehicular emission, it has not been included in the EIA for assessment with the AQO. This approach is consistent with all the previously approved EIA reports for highway infrastructures in HK.
However, it should be highlighted that the predicted O3 level has already been assessed in the modeling of background air quality, and that the effect of O3 (from various sources including those in PRDEZ, etc.) in the generation of NO2 has in fact been taken into consideration in the assessment. This Special Paper provides further explanations on this aspect.
2. Ozone as a Regional Issue
There have been extensive researches in O3 episodes in the Pearl River Delta Economic Zone (PRDEZ), in which different pollutant emission sources are located, including transportation, airports, power stations, industries etc. According to the research findings [1], [2], [3], [4], O3 is not a pollutant directly emitted from man-made sources, and the formation of O3 involves a complex interaction between a large number of chemical substances such as NOx and VOC when meteorological conditions (e.g. sunlight, temperature) “favour” such interaction. These findings also conclude that the formation of O3 is largely attributable to the cumulative effects of all the different emission sources within the PRDEZ, instead of just the emission sources in HK.
3. Various Emission Sources for NOx and VOC in the Region and in HK
It is therefore important to consider the regional NOx and VOC emission inventory.
3.1 NOx Inventory at 2031
Appendix 5D of the EIA Reports for HKLR, HKBCF and TMCLKL has presented the NOx emission inventory for 2031.
The NOx emission from PRDEZ would constitute about 85% and that from HKSAR would be about 15%. For the NOx emissions in HKSAR, the NOx from marine constitute about 45% and the emission from power station would be about 22%. The total from marine emission and power plant would add up to more than 65% already. Those from industries and vehicles would be about 9% for each.
As such, for the entire PRDEZ and HKSAR, the NOx emission from vehicular emission in HK would constitute only about 1.6% of the total NOx generated in the region. The annual NOx contribution from HKLR, HKBCF and TMCLKL is only 0.09% of the regional total. The following Tables 1 & 2 summarise the relative proportion of the NOx generation from different source groups in the PRDEZ and HK.
Table 1 : Comparison of NOx Emission in PRDEZ and HKSAR at 2031
|
Area |
Percentage |
|
PRDEZ |
85% |
|
HKSAR |
15% |
Table 2 : Comparison of NOx Emission in HKSAR at 2031
|
Emission
Source |
Percentage of
Proportion |
|
|
Groups |
% in HKSAR |
% in PRDEZ & HKSAR |
|
Aviation |
11% |
1.7% |
|
Power Stations |
22% |
3.3% |
|
Industries |
9% |
1.4% |
|
Marine |
45% |
6.9% |
|
Motor vehicles |
10% |
1.6% |
|
Non-road mobile source |
<0.1% |
<0.01% |
|
Commercial and domestic fuel combustion |
2% |
0.4% |
|
VOC Containing Products |
0% |
0% |
|
Biogenics |
0% |
0% |
|
Others |
<0.1% |
<0.01% |
|
Total |
100% |
13% |
3.2 VOC Inventory at 2031
As explained in the EIA Report, the prediction model has actually included the regional emission sources for different pollutants including VOC. Emission sources that have been incorporated in the model include transportation, airports, power stations, industries, biogenic sources, VOC containing sources etc.
The VOC emission from PRDEZ would constitute about 91% and that from HKSAR would be 9%. For the VOC emissions in HKSAR, the VOC containing products dominate the total emission by about 42%. Those from industries and biogenic sources would constitute about 11% and 28% respectively. The VOC generated from all the motor vehicles in HK would only constitute about 9%. The annual VOC contribution from HKLR, HKBCF and TMCLKL is only 0.01% of the regional total. The following Tables 3 & 4 summarise the relative proportion of the VOC generation from different source groups in the PRDEZ and HK.
Table 3 : Comparison of VOC Emission in PRDEZ and HKSAR at 2031
|
Area |
Percentage |
|
PRDEZ |
91% |
|
HKSAR |
9% |
Table 4 : Comparison of VOC Emission in HKSAR at 2031
|
Emission
Source |
Percentage of
Proportion |
|
|
Groups |
% in HKSAR |
% in PRDEZ & HKSAR |
|
Aviation |
3% |
0.2% |
|
Power Stations |
1% |
0.1% |
|
Industries |
11% |
1% |
|
Marine |
3% |
0.3% |
|
Motor vehicles |
9% |
0.8% |
|
Non-road mobile source |
<0.1% |
<0.01% |
|
Commercial and domestic fuel combustion |
<0.1% |
<0.01% |
|
VOC Containing Products |
42% |
4% |
|
Biogenics |
28% |
2.6% |
|
Others |
4% |
0.3% |
|
Total |
100% |
9% |
4. Assessment of Ozone Formation
As explained above, O3 is not a pollutant directly emitted from man-made sources and it involves a set of complex reaction chains between other pollutants including NOx and VOC. As it would takes several hours for these photochemical reactions to take place, O3 recorded locally (eg in Tung Chung) could be attributed to VOC and NOx emissions generated from places afar[5].
To model the long range formation of O3
(and other pollutants as well), the PATH model developed by EPD has been
adopted which has been implemented with the Carbon Bond IV photochemical
scheme, developed by the USEPA. This photochemical scheme constitutes 89
photochemical and chemical reactions.
It is a generalized chemistry scheme designed for simulating the major
features of the complex chemical processes in the atmosphere and has been
evaluated against approximately 170 experimental data sets of smog chamber
facilities from the
The assessment indicated that the maximum 1-hr O3 level in Tung Chung area in the assessment year of 2031 would vary with different meteorological conditions, with an average concentration of about 62 ugm-3. It should be noted that a portion of O3 would react with the NOx emissions from vehicles to form NO2 as reported in the EIA Reports.
5. Conclusion
The following summarises the reasons for adopting NO2 as the key indicator and not accounting O3 as a pollutant directly for this air quality assessment.
o The O3 generation from regional pollutants (ie NOx, VOC with appropriate sunlight and temperature) in the assessment year has been accounted for in the air quality modeling.
o Vehicles would not generate O3 directly but would however generate NOx and a smaller amount of VOC.
o Unlike NO2, the O3 formation by photochemical reaction would take several hours and O3 recorded locally (eg at Tung Chung) could be attributed to VOC and NOx emissions from places afar. Hence, the formation of O3 is largely attributable to the cumulative effects of all the emission sources within the PRD and the amount of VOC generated by the vehicles would have little effect on the O3 generation locally. (NB : The NOx from the Projects only constitute 0.09% of the regional total, while that the VOC from the Projects would constitute only 0.01% of the regional total).
o The NOx generated from vehicles would quickly react with the O3 in the background to form NO2.
o NO2 is therefore the key pollutant assessed in the EIA reports and this approach is adopted in all the other previous EIA Reports for highway infrastructure projects.
[1] Study of Air Quality in the
[2] Study of Visibility Reduction and its Causes in
[3] J.P. Wang, C. H. Fung, K. H. Lau, Integrated processes analysis and systematic meteorological classification of ozone episodes in Hong Kong
[4] Air Quality in Hong Kong 2008, by EPD, HKSAR Government
[5] Air Quality Objective Review – Public Consultation – Environmental
Bureau,