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ISSN: 1023-697X (Print) 2326-3733 (Online) Journal homepage: http://www.tandfonline.com/loi/thie20

Assessment of the Air Pollution Problems insidePublic Transport Interchanges in Hong Kong

Anthony C W Lo BEng MSC (EnvMgt) CEng MCIBSE MHKIE & Dennis Y C LeungBSc (Eng) PhD RPE CEng MInstE MIMechE MIOA MHKIE

To cite this article: Anthony C W Lo BEng MSC (EnvMgt) CEng MCIBSE MHKIE & Dennis Y CLeung BSc (Eng) PhD RPE CEng MInstE MIMechE MIOA MHKIE (1998) Assessment of the AirPollution Problems inside Public Transport Interchanges in Hong Kong, HKIE Transactions, 5:3,58-65, DOI: 10.1080/1023697X.1998.10667764

To link to this article: https://doi.org/10.1080/1023697X.1998.10667764

Published online: 09 Apr 2013.

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Assessment of the Air Pollution Problems insidePublic Transport Interchanges in Hong Kong

Anthony C W Lo BEng MSC (EnvMgt) (Eng MelBSE MHKIE

Department ofMechanical Engineering, The UnjversJty ofHong Kong

Dennis Y C Leung SSe (Eng) PhD RPE (Eng MlnstE MIMechE MIOA

MHKIE

Department 0/Mechanical Engineering, The University Of Hong Kong

This research alms to IdentIfY the problems that exist In the public tronsport interchanges (PTls) in Hong Kong. The studywas conducted through literature review, semi-structured Interview, site observation, foce-to-face questionnaire interviewand ventilation calcuiation. Based on the result of the questionnaire interview, most people commented that inadequateventilation was the main reason of the poor air quality inside PTis. Factors such as smOking habi~ health status,environmental conditions and seasonal variations were found to be associated with peapie"s perception and complaints.

The study revealed that most Of the PTls In Hong Kong were encfosed by structurol walls which would hinder naturofventilation. Under such circumstance, mechanical ventilation should be provided. However, most PTis in Hong Kong weredesigned with low level mechanical exhaust system which is Inefficient to capture vehicle exhaust gases. Instead, high leveiexhaust and low levef outdoor air suppfy system is found to be a more efficient and cost effective solution. The provision Ofan air-conditioned queuing enclosure to separate passengersfrom the source would be desirable. The air quality probfemsInsfde PTls can also be reduced to a certain extent through an Introduction Of stricter leglsfatlon and regulations.

Keywords: Public Transport Interchange, Air Pollution, Ventilation, Hang Kong

Introduction

Due to geographical constraints of limited road space, mixed and highdensity land use, high population growth rate, and a governmentaltransport policy Which discourages private car ownerShip, Hong Kongdepends more and more on public transport for its passenger movement.Public transport Interchanges (PTls) are vital in providing centrally locatedterminal facilities for resIdence and associated activities.

In this stUdy, PTls refer to those semi-enclosed or fully enclosed terminiwhich consist of Inter alia, all bus and minibus bays, taxi stands, carriageways, access roads, run-ins, passenger platforms, stacking areas andpassenger walkways. Table 1 shows the development of PTls In HongKong from 1966 to 2003 (Transport Department, 1997). By the year2003, the number of PTI will be increased by 60% over the existingnumber. The increment will be higher in the New Territories, due to higherpopulation increment in this region in the next decade. An implicationof this development suggests that PTls have played an important rolein public transport in Hong Kong in the past Their number would continueto increase despite of the rapid growth in railway services offered bythe Mass Transit Railway, the Kowloon and Canton Railway, and the UghtRail Transit networks.

Amongst the varIous types of vehicles inside a P"n, buses are widelyused for commuter journeys. Bus travel is local in character, with journeysmostly being to work, schools or shops. It is also one of the cheapestmodes of public transport in Hong Kong. In this regard, buses are thedominant passenger carriers in PTls and travelling services provided byminibuses, public light buses, taxis and private cars are consideredsupplementary.

Air Pollution Problems of Public TransportInterchanges

In 1992, the Environmental Protection Department (EPO) of the HongKong government received a number of complaints from commuters aboutthe poor air quality Inside some PTls in Hong Kong, especIally the lamTin and the Hong Kong China City PTls. In view of this situation, theEPD ,arrled out an air quality stUdy at Lam Tin PTI in July 1993. Resultsshowed that the air quality inside the PTI was unacceptable In terms ofS02 and N02concentratIon (1-hour) when compared with the Hong Kong

Year Hong Kong Kowloon New Sub-totalTerritorIes PTI Established

1966 0 0 1 1

1980 2 0 0 2

'981 0 0 0 0

1982 0 0 4 41983 0 0 1 1

1984 0 t 1 2

1985 2 0 0 21986 0 0 1 1

1987 0 0 0 0

1988 1 0 1 21989 1 0 1 21990 0 2 1 3

1991 0 0 0 0

1992 1 1 2 4

1993 0 2 0 2

1994 0 0 0 0

1995 1 2 2 5

1996 0 0 1 1

1997 to 2003 6 2 11 19' (Planned)

Table 1 - Devefopment af Public Transport Interchanges In Hong Kong(Transport Dept. 1997)

Air Quality Objectives (HKAQOs). The total amount of suspendedparticulates and the respirable suspended particulate levels were alsohigh. Moreover, the exhaust fans of this PTI were found running at only20% of their total capacity (Ylk et of., 1994). Subsequently, the EPD workedwith the Electrical and Mechanical Services Department (EMSD) to reviewand modify the mechanical ventilation system of lam Tin PT[, withparticular attention on the contaminated air intake and ventilationeffectiveness. However, complaints were still received trom commutersabout the poor air quality in this PTI after the modification (Tsang, '995).

At about the same time, the EPD conducted another study In November1994 on pollution control for four more PTls located respectively at Nam

mf-------------------------------------H::o:-n:-g:-K;;-o:-n::g:-/:::ns=t-::itu:-t:::io::n::o=1=E:::n-=g:::in-=ee=rs

Fung Center, New Town Plaza, UpTown Plaza and China Hong Kong City.The measurement data revealed that the hourly maximum concentrationsin Nam Fung Center and China Hong Kong City PTls had exceeded therespective limits set in the HKAQOs. Moreover, the concentrations ofgaseous contaminants at the 5-minute level in all four PTls were higherthan the hourly maximum limit of the HKAQOs. Fortunately, this constitutedless than 3% of the total time of operation (Ylk et al., 1994).

Diesel vehicles produce about 44% of all respirable particulates emittedin Hong Kong. and up to 75% of all ground level concentrations of nitrogenoxides (PELS, 1996). These vehicles are estimated to emit 10 times moreparticulates under urban driving condition than petrol vehicles, and 30to '100 times more than petrol vehicles fitted with catalytic converters.Diesel particles are of special concern, especially in confined space likethe present PTls studied. McClellan et a1. (1985) states that the concernstems from the recognition that:

• diesel exhaust particles are small in size, readily inhaled and depositedthroughout the respiratory tract with a substantial fraction in deeplungs;

• the relatively insoluble carbonaceous core of the particles results intenacious retention in lungs; and

• the cytotoxic and mutagenic properties of organic solvent extracts ofdiesel exhaust particles may result in functional diseases or cancers,especially of lungs.

As well as the known carcinogenic and mutagenic effects, other detrimentaleffects of diesel particulates include soiling of property and reducedVisibility. Foul and pestilent vapours that are usually smelly inside PTlsare all health threatening. Their occurrence is most acute when enginesare badly tuned and thus give out a lot of unburned hydrocarbon. Dieselexhaust gases consist of oxides of nitrogen, hydrocarbons, SUlphur dioxide,formaldehyde, odour constituents, smoke particulates and a relatIvelysmall amount of carbon monoxide. Their contents vary greatly with factorsSUch as the age of vehicle, carburettor adjustment, fuel quality, enginepower, level of vehicle maintenance and different driving habits of drivers.

Alms of Research

The air pollution prOblems inside PTls have not been adequately addressedIn the past due to inadequate resources. In this regard, not many stUdieshave been carried out in Hong Kong as well as in other countries. Thepresent study aims to identify the aforesaid problems in some selectedPTls in Hong Kong, with the fOllowing objectives to:

• collect perceptual data from people on air quality inside PTls,

• identify the fadors associated with people's perception and jUdgementon air quality inside PTls,

• determine an appropriate exposure time for people inside PTls,

• evaluate the impacts of air quality on the respiratory health of peopleinside PTls,

• review and comment on existing policIes of environmental controlon air quality inside PTls,

• evaluate and compare existing air quality guidelines and types ofventilation system for PTls, and

• formulate a method for designing the ventilation rate for PTls.

Scope of Study

This research is conducted through a combination of literature review,semi-structured interview, site observation, face-to-face questionnaireinterview and ventilation calculation.

Among the total thirty-two existing PTls on the Hong Kong Island, Kowloonand the New Territories, six were selected for preliminary stUdy on whethercomplaints of PT/s' air quality are related to their ventilation systems,architectural features or surrounding environmental conditions. Thisinformation is very usefUl to evaluate the cause of people's complaints

on the air quality inside PTI and provide physical evidence on verifyingthe results obtained In the face-to-face questionnaire survey to beconducted. The six PTls selected are Lam Tin PTI (in Lam Tin), WhampoaPTI (in Hung Hom). Lok Fu PTI lin Wang Tau Hom), Dragon Center PTI(in Shum Shui Po). Nam Fung Center PTI (in Tsuen Wanl and UpTownPlaza PTl (in Tal PoJ. During the site observation period, a pilot stUdywas carried out to find out the feasibility and appropriateness of condudingquestionnaire interviews inside the PTls.

Based on their locations, ventilation systems and architectural features,three of the six PTls were eventually chosen as the sites for face~to-face

questionnaire survey. These PTls were Lam Tin PTI, Nam Fung CenterPTI and Whampoa PT!. The surveys were carried out in August, Octoberand December of 1996 to generate information under different climaticconditions.

It is understood that certain information, such as the PTl's layout,governmental policies and survey findings, Is not published for publicaccess. Hence, semi-structured interviews were arranged with the relevantgovernmental departments and public utilities, for example, EPD, EMSD,Transport Department, Kowloon Motor Bus (1933) Company etc., in orderto obtain some of the essential unpubllshed information and directives.Table 2 summarises the scope and objectives of each stage of this stUdy.

Research Method Objectives

1. Semi-structured • obtain essential unpublished information andinterview government directives

2. Site observation • to identify:- layout of the PTis studied- vehicle movement- types of ventilation system- surrounding environmental conditions

• to rectify the results obtained in thequestionnaire survey

• to evaluate people's complaints on the airquality Inside the PTis

3. Face-to-face • to investigate people's subjective perceptionquestionnaire and judgment of the air quality inside PTlsinterview • to identify the associated factors that would

affect people's subjective perception andiudgment at air quality

• to determine the degree of thermal comfortinsJde PTls

• to verify seasonal effect on people's perception• to find out an appropriate exposure period

for people inside PTls• to find out the effect of poor air quality inside

PTls on the reported illness symptoms• to seek opinions on ways to improve the air

quality in PTls

4. Ventilation • to formulate a method for calCUlating thecalCUlation ventilation rate required in a PTI

• to evaluate the ventilation rate provided in theexisting PTls

Table 2 - Summary Of the Research Methods and their ObjectiVes

Site Observation Results

The general conditions inside and outside the six PTls were investigatedthrough site observation, Which were summarised in Table 3. It was foundthat complaints on the poor air quality inside these PTls are mUltifacetedIn nature. The causes of the poor air quality are evaluated below:

Lack oj Outdoor Air Supply System

Fresh outdoor air supply plays an important role in diluting theconcentration of pollutants and in prOViding a displacement effect onthe contaminated air in the queuing area and hence relieving thediscomfort of passengers.

=-:-:-::--:-:-----------------------------J!!I!IITRANSAalONS • Volume 5 Number 3 ..

Mechanical Ventilation System No. of Vehicle LanesPTI Location Surrounding % Of Nalural

Buildings Peripheral Ventilation PublicOutdoo, air supply EXhau,t Opening N Bu, light Taxi Others

bu,

Lam Tin Lam Tin Industrial High level High and loW level 5.3 No 8 2 2 1(belore amendment) (no amendment)Low level(after amendment)

Whampoa Hung Hom Residential Not provided High and low level 27.4 Yes 4 2 1 0

Lok Fu Center Wang Tau Hom Residential Not provided High and low level 43.6 Yes 7 0 0 0

Dragon Center Shum Shui Po Commercial Not provided High and low level 16.1 No 6 0 1 0

Nam Fung Center Tsuen Wan Industrial Not provided High and low level 52.3 Yes 7 0 0 0

UpTown Plaza Tai Po Residential Not provided High and Jow level 49.4 Yes 9 0 0 0

#: "Yes" denotes "most likely to occur". "No" denotes "less likely to occur".

Table 3 - Summary oj Site Observation Findings Of the Six PTis

As shown in Table 3, mechanical outdoor air supply system Is providedIn lam Tin PTI only. The air supply of the other five PTls relies entirelyon the outdoor air induced via the peripheral openings. Under thiscondition the openings should be sufficiently large and evenly distributedfor better entrainment of air. Moreover, the ventilation fans shOUld bedesigned to create an extremely large airflOW rate to maintain a negativepressure inside the PTls. As the outdoor air supply might not be evenlydistributed, energy for fan operation would be wasted.

Inadequate Natural Ventilation

Natural ventilation has the advantage of enhancing the effectivenessof the mechanical ventilation system and saving energy by reducingthe frequency of operating the ventilation fans. However, the headroom(minimum 6 meter) of all PTls in Hong Kong is relatively low in comparisonwith the height of a bus of about 4.5 m. During peak hours, air flowpattern may be disrupted by the presence of many stationary buses.This would result in the stratification of air, with little or no air movementinside the PTj, thus increase the pollutant concentrations. Moreover, LamTin and Dragon Center PTls showed the lowest percentage of area openln&Which implies that the natural ventilation would be less than other PTls.

light vehicles. ThUS, the outdoor air quality of these PTls might be betterthan that in Tsuen Wan and Lam Tin. Intake of good quality ambientair is the primary means of diluting indoor pollutant concentration.

Inappropriate Design Of Ventilation System

Exhaust air grilles are usually installed at low level to immediately capturethe exhaust gases emitted from bus exhaust pipes. However, experimentsshowed that it was ineffective for these exhaust air grilles to capturethe exhaust gases (Brociner, 1990). Hot exhaust gases rise up to highlevel immediately due to buoyancy. It was impossible to maintain asufficiently high suction velocity at the exhaust air grilles to capture allthe exhaust gases. After a whlle, the exhaust gases then diffuse or driftdown to other parts of the PTI and the whole area would be contaminated.From the obselVation, all the six PTls were designed with low level exhaustgas extraction system as shown in Figure 1. As the ventilation effectivenessof this type of system is low, it seems that there is an urgent need forthe EPD and the EMSD to review the ventilation systems installed inexisting PTls in Hong Kong.

Qutlulng LaneBus LaneQueuing Lane

J.. I -1-. High Level J.. i J..->I \c ->I\c Exhausl ->I ,,- ->I \c

I I

I II (IUS , I

I I Low levelLow Level ExhaustExhaust

+- ~:::---, 0 ~ ~f-L1+, . .. . .

Figure 7 - Schematic Diagram Of Ventilation SystemHigh Level and Low Level Exhaust in PTls

Poor air distribution can also be caused by 'short circuiting" in whichthe supply air Is exhausted without diluting the gaseous pollutants. Thishappened in Lam Tin PTI where the headroom was relatively higher thanthat of the other five PTJs. Both the supply and exhaust air grilles werelocated at high levels. The supply air was exhausted through the exhaustair grilles before reaching the breathing zone of passengers or drivers.In view of this, the government modified the system in Lam Tin PTI in1995 by blocking aff the supply air grilles at high levels and extendingthe air ducts downward so that air would be supplied at mid-level. Adrawback of this modification, however, is that the distribution of airflowis poor at low levels (Lo, 1997).

Exhaust ran

To Ouldoor*-r -,-, - -- -,- T"Poor Outdoor Air Quality

The pollutant concentration in the ambient air outside PTI is a criticalfactor in determining the effectiveness of the ventilation system. Intakeof outdoor air with poor quality will make the condition even worseunless special treatment is prOVided, which is usually not considereddue to economic reasons.

Lam Tin and Nam Fung Center PTls are located at the west of KwunTong and Tsuen Wan respectively which are classified by the EPD asindustrial areas because of the existence of many factories nearby (EPD,1996; Planning Department. 1996). The openings of Lam Tin and NamFung Center PTls are also directly facing the major trunk roads. KwunTong and Tsuen Wan areas had been exposed to unacceptably highconcentration of SOl emanating from industrial premises (PlanningDepartment, 1996). In July 1993, the EPD conducted a measurementat Lam Tin PTI and recorded an episode with an hourly maximum S02concentration of 910 )lglm3 , Which was 14% higher than the HKAQOs.The maximum concentratlon recorded in the EPD's Kwun Tong MonitoringStation was also high at 787 ~g1m' (EPD, 19931, probably due to anabrupt change in climate during the day. The report concluded that airpollution inside the PTI would be aggravated by poor meteorologicalconditions in the atmosphere. The intake of contaminated outdoor airto the PTI would offset the dilution effect of the mechanical ventilationsystem on the vehicle exllaust gases inside the PTJ.

To the contmry, Whampoa and Lok Fu PTls are located in residentialdistricts and are surrounded by minor roads Which are used mainly by

mf------------------------------------------;-H;:o-=ng-::-:K;:o-=n-=g--:j-=ns:::t:::n:::ut:;:o:::n=-=Oj-;;:En=-g:::;-=ne=-e=rs

>15

•

6·10 11·15

Time (mlnutes)

5 Of less

1('%

40% t"------tJll--'i::---='-----j50% r--:o---~~-=----,

Pen:entaga01

lrnelViewee

Inappropriate Fan Operation

The existing ventilation fans In most of the PTls are designed with atimer to control their operation periodically. The timer needs to be seton site to suit the actual surrounding environmental conditions and trafficflow patterns. However, this practice, though can save energy, is notan appropriate air quality control measure. To control the aIr quality insidePTIS, the opemtion of the ventllatlon system should be monitored andcontrolled automatically by gaseous pollutant sensors such as CO andN0

2sensors. Unfortunately, none of the existing PTls In Hong Kong has

installed this type of monitoring and control system.

Figure 3 - Diseases Reported by teh Interviewees

f.!!r!I",

70%

60%.<'

50%

40%

30% .~

20%

'0%

0%

:: +=::;::====~;=:;-:;;:;;:::::::===~~:il35%

20%15%

10%5%0% .L.~'

AdI'tI2 ~ .E~&"'" l""llalIlo'.... <IsAoIc

Disease

Percentage 01IntelViewee

l:l umTln[) Nam Furlg,,.. .

Percentage ofInterviewee

Figure 2 - Average Waiting Time Inside PTIS

lack of Understanding Of PTrs Daily Operation

Inappropriate design and poor maintenance of ventilatIon systems areprimarily the result of a lack of understanding of the dally operation ofa PTJ. This can be avoided at an early stage if architects, engineers andbus companies have a better communication and understanding of thehealth and comfort problems inside the PTls. They must ensure that theventl1atlon system is capable of meeting the established air qualitystandards.

Lack Of Maintenance Of Ventilation EqUipment

It was found that exhaust air grilles of most of the PTts visited werevery dirty and clogged with dust. This would reduce the free area ofthe grilles and would further degrade the effectiveness of the ventilationsystem. Ventilation system must be regularly and properly maintainedin order to effedively control the Indoor environmental conditions.

Inappropriate Operation Of Bus Engine

During the visit to the six PTls, it was found that some of the bus engineswere turned on unattendedly (Le. Without passengers inside the bUs)especlally during lunch hours. Some bus drivers turned on the bus enginesin order to switch on the air-conditioning system and took rest insidethe bus. The emission of gaseous pollutants from these buses wouldfurther degrade the air quality inside the PTls and reduce the overalleffectIveness of the ventilation systems.

Disease

Summaries of the Important Findings from theQuestionnaire Survey Agure 4 - Influence Of Air Quality on the Reported Diseases

Figure 5 - RankIng of Factors

Factor A denotes ~Poor mechanical ventilation system for extractingvehicle exhaust gas".Factor B denotes MThe engine is on when the vehicle is withoutpassenger inside".Factor C denotes "Use of diesel fuel for vehicles".Factor 0 denotes "Poor outdoor air introduced into this covered PTI".Factor E denotes "Others".

1.'5 lam TinliJ Nam Fung:lJ Whampoa

PTI

Whampoa

Nam Fung

Factor

60"k

50%

40%

30%

20%

10%

0%D B A

TO supplement the above site observations, an extensive questionnairesurvey was conduded in three of the PTls (lam Tin, Nam Fung Centerand Whampoa) to find out people's subjective perception and appraisalof the environment inside the PTls. These PTIs were selected on the basisof their own characteristics In ventilation system deSign, architeduralfeatures, locations and surrounding openings. The response of theinterviewees to the questionnaire can refled their degree of satisfactionon the environmental conditIons inside the PT's. The overall stUdypopulation was 1181 people, of whom over 65% belonged to the agegroup of 18 to SO and more than 96% were passengers. The significantquestionnaire findings are summarised as follows:

3. The waiting time of passengers inside the PTls varies with locationsand times. It was found that more that 50% of the Interviewees hadto walt for 10 minutes or less (Figure 2). Based on this finding anexposure period of 10 minutes would be suitable for designing theventilation system of all the three PTls.

b. The results of the Influence of air quality on interviewee's health areshown in Figures 3 and 4. All the three PITs stUdied have similar trends.Eye and nasal allergies were the diseases most frequently reportedby the Interviewees, followed by throat Irritation. Among this groupof Interviewees. a high percentage of people in Lam Tin PTI reportedthat the perceived air quality had an adverse effect on their health.The prevalence of asthma, bronchitis and lung diseases varied from2% to 9% and were comparatively lower than other diseases. Overallspeaking, the extent in which the PTl's air quality was felt to affectthe interviewees' health was the greatest for Lam Tfn PTI, followedby Nam Fung Center PTI, and Whampoa PTI had the smallest extentamong the three PITs studied.

------------------------jl/llTRANSACTIONS' Vaiume 5 Number 3

Figure 6 - Seasonal variation of (a) Air Quality Perception (b)Temperature perception

- -Lam TinI---Nam Fung

- - ·Whampoa

c. Most interviewees regarded that 'poor mechanical ventilation systemfor extracting vehicle exhaust gas' was the main factor leading topoor air quality Inside the PTJs (Figure 5).

d. Figure 6 shows the seasonal variations on air quality perception andperception of temperature respectively. A score of 1 indicates an idealcondition and a score of 5 indicates an unacceptable condition. Thescores for air quality and thermal stress decreased significantly fromAugust to December in all of the three PTls studied. This findingsupported the assumption that seasonal changes might have an effecton people's perception on both the air quality and temperature insidePTls.

e. The complaints from commuters on the poor air quality inside PTlsare not solely due to physical factors. FIndings in the Chi-square testsshowed that perceived air quality was significantly associated withsmoking habit, health status, thermal stress, noise level and illumination.

f. The perceived air quality of the 3 PTls was rated by the intervieweesand shown in Figures 7. Regardless of the month in which the interviewswere carried out, the perceived air quality was the worst for Lam TinPTI in all the three months studied (I.e. August, October and December).The air quality of Whampoa PTl was perceived as the best incomparison with the other two PTls.

Assessment of Ventilation Rates in a PTI

Dec

.~ .

lit:'

~~"""'::""'"

Oct Dec

Month

Oct

Month

.'"':zl' "" -'"',t. .' .,." ,

~ t~:;"""": ~. ~,-':3 j:-~_~=--L_~_~'_.---'

Aug

4

Averagescore

Averagescore

(b)

(al

(a) 100%

80%-o ~~ ~ 60%:ir"e .~8 ~ 40%, -~.fa.

20%

0%

There 15 no statutory requirement or regulation in Hong Kong that governsthe criteria in determining the ventilation rate for PTls. In the past,ventilation systems for PTls were normally designed according to theTechnical Schedules of Agreement and Conditions of Grant of a minimumof 15 air changes per hour. It seems that this rule~of thumb figure doesnot have sufficient technical support. Rather, the air quality guidellnesrecommended by the EPD (Table 4) may be more appropriate for design.It should be noted that these guidelines are more stringent than otherinternational occupational health standards (La, 1997).

Lam TinPollutanl Source Concentration Average Time

(~g/m')

(a) Sulphur Dioxide 1,000 5 minsBOO 1 hour

(b) Nitrogen Dioxide 1,800 5 mins300 1 hour

(e) Carbon Monoxide 115,000 5 mins30,000 1 hour

Expressed at the reference condition of 298K (2S"C) and 101.325 KPa (one atmosphere).

Table 4 - Air Quality Guidelines Recommended by the EPD for PTfs

f· ,

Nam Fung Whampoa

PTI

0%

80%

(b) 100% rrch+F""'li i1F:::::::::~n

PTJ

, m Very poor 0 Poor [] Fair [I Good • Very good,

Figure 7 - Air Quality perception in (a) August (b) October and(ci December

Evaluation Of Ventilation Rate

Vv'hen estimating the ventllatlon rate for a PTI, one should consider carefullythe layout of the PTI, the number of vehicles expected over peak hours(including both moving and idling vehicles), travelling distance insidethe PTI, travelling speed of vehicles inside the PTI, emission factor/rateused for travel11ng and idling vehicles, conversion rate of NO to NOl ,

ambient pollutant concentration and air quality requirement Inside thePTL Moreover, the following assumptions have been made In theassessment of ventilation rates in order to simplify the calculation;

• The ventilation rate, ambient air concentration and generation rateare constant under steady-state condition and the air inside the PTIis perfectly mixed.

• Natural ventilation is negligible under tile worst condition.

• A diesel engine produces mainly NO, part of which would be Qxidisedto N0

2In the ambIent air. A conversion factor of 20% Is assumed

in the calculation of ventilation rate (Holmes and SaJusbury, 1988;PJARC, 1987).

PTJ

Nam Fung Whampoalam Tin

40%

20%

60%

(c)

80% i.'ilb,

m---- Hong Kong Institution Of Engineers

The air quality inside a PTI with a high percentage of diesel vehicleswill most likely be affected by NO:! and CO emission (Holmes andSalusbury, 1988; ASH RAE, 1995). Thus, the required ventilation ratedepends upon the number of buses travelling and unattended insidethe PTI as well as the pollutant emission factors of buses. Equation (2)

is modified for travelling and idling situations as fOllows:

• A fixed arrival and departure schedule is assumed over the peak hours.The bus enters and leaves the PTI at a lO-minute interval per lane(data obtained from the questionnaire survey), Le. J2 buses per hour.

• The travelling speed inside the PTI is 10 km/hr.

• Each bus lane is assumed to be occupied by an energIsed bus fortwo-thirds of the period. Hence, the PTI will be occupied by theenergised buses in two-thirds of the lanes.

• The 99th percentile pollutant concentration level measured at theneighbouring EPD's monitoring station is assumed to represent theambient pollutant concentration level surrounding the PTls.

Having taken into consideration of the above-mentioned factors, theconcentration of pollutants bUild-up inside a PTI can be predicted usingthe following mass balance equation:

dCV dt

O

~Q(C,-C)+q (1)

whiCh, under steady-state condition, gives

Q~q/IC,-CJ

Travelling; QT~ q.DT.D / CJ1-C!C)

Idling:Q, ~ q.D, .L / Col1-C!C)

(2)

(3)

(4)

Total Exhaust Ventilation RateRequired (m3/s) lor Achieving the Acluallnstalled

EPD's Recommendations Exhaust VentilationPTt Rate (m'/s)1-hr exposure 5-min exposure

period period(Ylk ot al. 1994)

CO NO, CO NO,

Lam Tin 5.31 327.7 1.33 30.5 150

Dragon Center 3.4 237.3 0.86 20.8 Not measured

Whampoa 2.1 213.9 0.52 13.8 Not measured

Lok Fu 405 :lIll7.1 1.02 25.2 Not measured

Tal Po 5.87 319.01 1.48 33.8 377

Nam Fung 3.87 274.4 0.97 24.4 105

Table 5 - Comparison of Estimated Ventl/atlon Rates with Actual InstalledValues

Lam Tin Nam Tai Po LimitFling recommended

by the EPO

NO, (~g/m') 5-min 79B 5BB 1,233 1,800

1·hour 300 199 287 300

CO I~g/m') 5-min 11 ,900 8,230 21,150 115,000

1~hour 11,100 52,000 4,400 30,000

Table 6 - 5-min and 1-hour Concentration of Gaseous Contaminantsmeasured in Lam Tin, Nom Fung and To; Po PTJs (Yik et 01. 1994)

The ventilation rate for extracting NO:!, CO and other gaseous pollutantsunder travelling and unattended conditIons can be evaluated bysubstituting the respective pollutant emission rate q and concentrationCo and Cr Although S02 and suspended particulate are also constituentsof bus exhaust, they have not been considered in this calculation because:

a. the maximum sulphur content of all diesel vehicles has been reducedfrom 0.2% to 0.05% by weight from 1 April 1997. It Is anticipatedthat Its contribution to air pollution inside PTls has been reducedsignificantly.

b. it is difficult to have the ventilation rate calculation based on suspendedparticulates because the concentration depends on the conditions ofengine as well as the ventilation filtering system. Furthermore, manyresearch studies considered N02 and CO as the major contaminantsin the design of ventilation system for PTls (Holmes and Salusbury1988, A5HRAE 1995 and Ylk et at. 1995).

Results

The calculated ventifatJon rate required for each of the six PTls to maintainthe S-min and 1-hour average concentration level of N02 and CO issummarised In Table 5. The reSUlts show that the ventJIatJon rate requIredto keep N02 level at both 5-min and 1-hour concentratIon levels Is muchlarger than that of CO. This result agrees with the studies conducted byA5HRAE (1995), Holmes and 5alusbury (1988) and Ylk et al. (1994) thatNO~ concentration Is a critical parameter when determining ventilatlonrequirements.

In addition, the results show that the existing ventllation rates installedare only sufficient for maintaining the pollutant level at a 5~min exposureperiod. This agrees with the result of measurement shown in Table 6,which was conducted by the EPD in 1994 at lam Tin, Nam Fung Centerand Tai Po PTls. The S-min concentration of N02 and CO is well belowthe EPD's recommended air quality requirement while the hourly valuesare closed to the recommended values.

The existing ventilation rates installed in the 5 PTls (except Tai Po PTI)are much less than that calculated for keeping the pollutant level at a

l-hour exposure period. Based on the EPD's measurement, however, itwas claimed that the pollutant level could still be maintained Within theEPD's recommended air quality requirement, but in a marginal condition.From this perspective, the existing ventilation systems and air qualitycriteria should be reviewed.

Deficiencies of Existing Policies on Air PollutionControl Inside PTls

Up to now, no legislation has been specifically designed for controllingthe air pollution problems Inside PTls in Hong Kong. Even though theAir pollution Control Ordinance (APCD) was enaded for more than fifteenyears, several deficiencies Inherent tn existing environmental policieson air pollution control inside PTls can be identified as follows:

a. The APCO is limited to atmospheric pollution. The air pollutant nuisanceincludes emissions -prejudicial to pUblic health". But this provIsionwas not designed to regulate the health and safety in work place orprotect public health from vehicle gaseous pollutants generated insIdePTls.

b. The newly issued Practice Note on Control of Air Pollution in Semi­confined Public Transport Interchanges and the Hong Kong PlanningStandards and Guidelines are guidelines only, which are notstatutory requirements for developers and polluters. It will be thesame for the Practice Note on the deSign of ventilation system ofPTls.

e. There are neither any standards nor accepted clear guidelines regardingventilation system design and operation inside PTls.

d. The fuel sulphur limit for automobile diesel has been reduced from0.2°/0 to 0.05% on 1 April 1997. The problem of SUlphur dioxideand particulate emission can be improved but the Improvement maybe offset by poor maIntenance of vehicles.

e. Proposals on phasing out the use of diesel fuel are not aimed at busesthat are the main contributors of air pollution inside PTls.

f. It is difficult to implement penalty for offence of poor air quality inside

==~~~.-:--------------------_.-­TRANSAC7IONS • Volume 5 Number 3 IIlIlII

PTIS because both the government and users (I.e. bus company) havetheir responsibility to maintain an acceptable air quality.

g. Punishment or penalty was not stipulated in any ordinance or legislationto deter the drivers from turning on vehicle engines unnecessarilywhen the buses were not in service (Le. during unattendedcondition).

g. The EPD claims that the persistence of polluting actlvltles Is due tothe inadequate resources to carry out the regular monitoring work.To a certain extent, the lack of resources poses a problem inenforcement. However, continuous monitoring Is vital to ensure thedesigned ventilation rate is appropriate to the actual situation insidethe PTis.

Discussion and Recommendations

Most of the PTls in Hong Kong are enclosed by structural walls to supportthe development of a podium above. The size of the surrounding openingon the structural wall is limited by the buildings constructed and thiswill hinder natural ventilation. Under such circumstance, mechanicalventilation should be provided. However, the mechanical system designof PTls is usually impractical. The PTls in Hong Kong are always designedWith low level exhaust system which has been proved inefficient to capturevehIcle exhaust gas. By the evaluatlon of various types of ventilationsystems, it was found that high level exhaust and low level outdoor airsupply is the most efficient and cost effective solution (la, 1997). Thefollowing points are recommended for designing the ventilation systemof a PTI.

a. Outdoor air to be introduced into a PTl should come from anuncontaminated area.

b. Exhaust air outlets should not be directly facing the neighbouringresIdential buildings.

c. Short-circuiting of the ventilation, in which incoming air is notadequately circulated before being extraded, should be avoided.

d. Gaseous pollutant sensors should be installed to monitor and controlthe operation of ventilation fans rather than using timer control.

e. Filters should be used to remove suspended particulates and shouldbe cleaned regularly.

f. Opening surrounding a PTI should be maxImised to enhance naturalventilation.

It should be noted that the ventilation calculation in this paper is basedon the need to achieve the air quality requirement recommended bythe EPD. It depends on the pollutant concentrations of ambient airsurrounding the PTls. In the absence of such data, the 99th percentilepollution level monitored at the nearest monitoring station Is used inthe assessment to represent their respective ambient level. It is not possibleto correlate these values with the actual ground level pollution prevalentat each PTI. However, the monitoring stations are not located on thestreet level where higher concentratlons would usually occur, thereforethe calculated result would be more conservative than the adual values.Nevertheless, the above flndings should be treated as preliminaryIndications only for achieving ventilation requirements. During the actualoperation of the ventilation system, the users' perception or scientificmonitoring results may indicate that a higher or lower ventilation rateIs more appropriate.

In light of the discussion on the deficiencies of existing environmentalpolley control, it can be concluded that dramatIc Improvements in airquality inside PTls has not been realised. It is mainly due to theineffectiveness of existing legislation and lack of monitoring programs.The success of any environmental law ultimately depends on the rigourand integrity of its enforcement. Hence, it is doubtless that a packageof statutory policies is needed to address the air pollution inside 1'Tls.The environment In PTls would be improved If the drafting Of legisla.tionis more accurately reflecting the needs of air quality requirement insidePTls.

Conclusion

This stUdy is focused on Investigating the air pollution problems insidethe PTls in Hong Kong and reviewing the environmental policy controlin this aspect. There is neither a specially designed air quality requirementnor well-accepted ventilation standard for the PTls in Hong Kong. Thesite observation of the six selected PTls Indicates that poor air qualityinside PTIs Is multifaceted in nature. There are at least eight differentcausal agents: I) lack of outdoor air supply system; ii) inadequate naturalventilation; iii) poor outdoor air quality around the PTI; iv) inappropriateventilation system design; v) inappropriate fan operation; vi) inappropriateoperatlon of bus engine; vii) lack of maintenance of ventilation equipment;and viii) inadequate understanding of PTI's daily operation. The calculationshows that the flow rates of existing ventilation system cannot produceair quality up to the EPD's recommended levels. Hence, the air qualityslandards and ventilation requirements for PHs In Hong Kong shouldbe reviewed.

The PTIs In Hong Kong are always designed with low level exhaust systemwhich has been proved inefficient to capture the vehicle exhaust. Byevaluating various types of ventilation systems, high level exhaust andlow level outdoor air supply Is found to be the most feasible and costeffective solution.

Based on the interview, most people commented that inadequateventilation is the main factor for the poor air quality Inside PTls. Actually,smoking habit, health status, environmental conditions like thermal stress,illumination and noise levels, and seasonal variations were found to beassociated with people's perception and complaints. Hence, an air­conditioned queuing enclosure to separate the passengers from the PTIenvironment can be considered for those highly polluted PTls.

It is unrealistic to expect all diesel vehicles running inside the PTls bereplaced by vehicles using other cleaner alternative fuels or electricityin a short time. The most viable short-term solution is to Improve thePTls' ventilation systems so as to maIntain an acceptable all' quality throughproper control, operation and maintenance.

It Is hoped that the air quality problems inside PTls can be reduced toa certaIn extent through the above recommendations. In the long run,suitable legislation and regulations shOUld be introduced to control andsolve the problems in a cost-effective manner. In addition, a comprehensiveresearch and survey strategy should be formulated to put more emphasison pollutant specific health risks and means of minimising people'sexposure to pollutants.

Acknowledgement

The authors wish to acknowledge the Croudler Foundation for sponsoringpart of the stUdy.

References

1. American Society of Heating. Refrigerating and Air-Conditioning Engineers(ASHRAEj (1995). 1995 ASHRAf Handbook - HVAC Applications. Atlanta: ASHRAE.

2. Broclner, A. (1990). Bus Terminal Solves Ventilation Problems. Heating, Pipingand Air Canditioning Journal. April, 1990,79-87.

3. Environmental Protection Department. Hong Kong Government (1993). Air Qualitystuay Of the Lam TIn Transport Inlerchange. Report No. EPD1TP14/93. HongKong Government Printer.

4. Environmental Protection Department Hong Kong Government (1996). Air Qualityin Hong Kong 1994, Hong Kong Government Printer.

5. Holmes, MJ. and Salusbury, T. (1988). Ventilation Design for a Bus Station.9th AIVC Conference, Gent Belgium, 12-15 September 1988. UK: Air lnfUtrationand Ventilation Centre.

6. Le, A.C.W. (1997). Environmental PoJictes and Complaints of Air Pollution Insidethe Public Transport Interchanges in Hong Kong. M5c Dissertation, The Universityof Hong Kong.

7. McClellan, R.O., Mauderly, J. l., Jones, R.K. and CUddihy, R.C. {l98S}. Hea!thEffects of DIesel Exhaust: A Contemporary Air Pollution Issue. PostgraduateMedicine. Lovelace Medical Centre, 78, 199-206.

8. Permanent International Association of Road congress (PIARq (19B?). Technical

Hong Kong Institution 0/ Engineers

Nomenclature

Co =

l-(C,ICJ -

D =

D, -

Dr -L ~

M, -

q -

Q =

Q, -

Comm;ffee Report NO.5 on Road Tunnels, XVIII World Road Congress, Brussels,September 1987.

9. Planning Department. Hong Kong Government (1996). Hong Kong PlanningStandards and Guidelines, Hong Kong Government Prlnler.

10. Planning, Environment and Lands Branch, Hong Kong Government(l996).Heoding Towards Sustainability: The Third Review Of Progress on the1989 While Paper, Hong Kong Government Printer.

11. Transport Department, Hong Kong Government (1997). Private communicationwith Hong Kong Transport Department.

12. Tsang, Y. F. (I995). Air Pollution in Lam Tin 8us Terminus (in Chinese), SingTao Daily, 30 September 1995.

13. Ylk, W.H., Viu, J. and Burnett. J. (1994). A Siudy on PoIlu/ion ContrOl for Enc/ose(l8us Terminus. Hong Kong Environmental Protection Department.

14. Vik, W.H., Vlu, J. and Burnett, J. (1995). Air Conditioning and MechanicalVentllatlon DesIgn for Queuing Enclosures In a Bus Terminus. Building ServicesEngineering Research Technology, 16, 9-16.

= Pollutant concentration in the make-up air of ventilationsystem (gIm')

Pollutant concentration inside PTI (gImJ )

Factor for ambient outdoor pollutant concentration

Travelling distance (m)

Number of vehicles idling per lane (veh/lane)

Number of travelling vehicles per meter = Mu/v

Number of lane

volume of travelling vehicles per second

Emission rate of vehicle exhaust gas (gls)

Ventilation rate (m 3/s)

Calculated ventilation rate for vehicles under idlingcondition Im'I,)

0T = Calculated ventilation rate for vehicles under travellingcondition (m3/s)

v = mean driving speed of vehicles (mfs)

V == Volume of enclosed PTI (m3)

TRANSACTIONS' Volume S Nt/mber 3

Anthony C W Lo

lr Anthony Lo received his BEng (Hons) in BuildingServices Engineering wIth Fltst Class Honours from theHong Kong polytechnic University In 1993. He joinedParsons Brlnckerhoff (Asia) Ltd. after graduation andwas promoted to Senior Building Services Engineer in1996. Mr La obtained a MSc degree In EnvironmentalManagement with DistInction at the University of HongKong in 1997 and was awarded the Ada and ArthurHill PrIze. He won the Fred Kan a Co Prize 1997 andthe 1997 Best Environmental Paper Award from the

Environmental Division of the Hong Kong Institution of Engineers for his studyon the pollution problems in pUblic transport Interchanges in Hong Kon.

Dennis V C Leung

Ir Dr Leung received his BSc(Eng) and PhD from theDepartment of Mechanical Engineering, The University01 Hong Kong. He worked in the Hongkong Electric Coltd as an Envlronmental Engineer during the period1988-1993. In March 1993, Dr Leung returned backto the Unlverslly of Hong Kong to take up a lecturerpost in Air Pollution In the Department of MechanicalEngineering. He Is currently an Associate Professor andhas publiShed over 60 technical papers in the field ofaIr pollution control, dispersion modelling ilnd energyconversion.