Problems & Solutions

Cleaning the Air at Street Level

Street Level Air Pollution

In our busy streets, air pollution is mainly caused by motor vehicles, particularly diesel vehicles such as trucks, buses and light buses which emit a large amount of particulates and nitrogen oxides. The pollutants are often trapped at roads flanked by very tall buildings, thereby causing the roadside levels of respirable suspended particulates (RSP) and nitrogen dioxide (NO2) to exceed the Air Quality Objectives over the years.

Photo of busy traffic


A Comprehensive Vehicle Emissions Control Programme

The Government has been working for years to control emissions from motor vehicles. Although there had been progress made, such as the tightening of vehicle emission standards, the improvements from these measures had tended to be offset by increases in emission from the continue growing vehicle numbers and kilometres driven.

Chart of Growth in vehicle number and mileage

Therefore, in 2000 the Government pressed ahead with an enhanced programme to address the problem. The programme aimed to reduce particulate emissions from motor vehicles by 80% by the end of 2005, and nitrogen oxides emissions by 30%. The main initiatives included :

  • Adopt tighter fuel and vehicle emission standards;
  • Adopt cleaner alternatives to diesel vehicles where practicable;
  • Control emissions from the remaining diesels with devices that trap pollutants;
  • Strengthen vehicle emission inspections and enforcement against smoky vehicles; and
  • Promote better vehicle maintenance and eco-driving habits.


The Government earmarked $1.4 billion for this programme. The investment was for providing grants to owners of diesel taxis and light buses for switching to cleaner alternatives, and for helping owners of older pre-Euro diesel vehicles to install devices that trap pollutants.


New Initiatives in 2007

To strengthen the effort to improve roadside air quality, the Government launched on 1 April 2007 new measures to reduce vehicle emissions:

  • Provide a one-off grant to encourage vehicle owners to replace their pre-Euro and Euro I diesel commercial vehicles with new commercial vehicles complying with the prevailing emission requirements for newly registered vehicles, which, at that moment, was Euro IV standard. The deadline for owners of pre-Euro diesel commercial vehicles to apply for the grant has been extended from 30 September 2008 to 31 March 2010 (which is the same as that for the Euro I models). The Government earmarked 3.2 billion for this programme.
  • Offer a 30% reduction in first registration tax to buyers of newly registered environment-friendly petrol private cars, subject to a ceiling of $50,000 per car. Environment-friendly petrol private cars emit 50% less hydrocarbons and nitrogen oxides and consume 40% less fuel than conventional Euro IV petrol private cars.  In June 2011, the FRT reduction rate has been raised from 30% to 45%, subject to a cap which has been increased from HK$50,000 to HK$75,000 per car.

New Initiatives in 2008

Starting from 1 April 2008, buyers of newly registered commercial vehicles meeting the qualifying standard for environment-friendly commercial vehicles, which is set at Euro V level, will enjoy concessions for their first registration taxes. Compared with Euro IV vehicles, Euro V heavy duty diesel vehicles emit about 40% less nitrogen oxides (NOx). For light duty diesel vehicles, Euro V models emit about 80% less respirable suspended particulates and 30% less NOx. As regards Euro V petrol/LPG vehicles, they emit about 30% less NOx.


Progress of Major Initiatives

Tighter fuel and vehicle emission standards

Vehicle emission standards - Emission standards for newly-registered vehicles have been progressively tightened since 1995. The most recent change is in 2012, when we implemented Euro V emission standards. A Euro V diesel vehicle emits about 95% less particulates and 78% less nitrogen oxides than a pre-Euro vehicle manufactured before 1995.

Comparison of Vehicle Exhaust Emission Standards - Large Diesel Vehicle (>3.5 Tonnes)

Comparison of Vehicle Exhaust Emission Standards - Large Diesel Vehicle (>3.5 Tonnes)


Vehicle fuel standards

  • Petrol - We have tightened the sulphur content in unleaded petrol from 0.015% to 0.005% since January 2005 in tandem with the European Union.
  • Ultra low sulphur diesel (ULSD) - ULSD has a sulphur content of 0.005%, which is the Euro IV requirement for motor vehicle diesel. It became the only motor diesel fuel available at petrol filling stations in Hong Kong, after the Government introduced a concessionary duty on ULSD in July 2000. Since April 2002, ULSD has been the statutory minimum requirement for motor vehicle diesel, 3 years ahead of the European Union. Hong Kong is also the first place in Asia to introduce ULSD on a full scale for its vehicle fleet.
  • Euro V diesel - On December 1 2007, the Government offered a concessionary duty rate of $0.56 per litre for Euro V diesel, which has a sulphur content of 0.001%. Since then, all petrol filling stations in Hong Kong are exclusively offering this fuel. Starting from 14 July 2008, the duty rate for Euro V diesel has been waived to further encourage drivers to use this more environment-friendly fuel. Euro V diesel is suitable for all existing diesel vehicles. As compared with ULSD, fuelling existing diesel vehicles with Euro V diesel can reduce their sulphur dioxide and particulates emissions by 80% and 5% respectively.
  • Biodiesel - In January 2010, the Legislative Council approved the Air Pollution Control (Motor Vehicle Fuel) (Amendment) Regulation 2009. The Amendment Regulation provide for the statutory control on the specifications of motor vehicle biodiesel and the labelling requirement on selling of motor vehicle biodiesel with biodiesel content over 5%. The Amendment Regulation will come into operation from 1 July 2010.
  • Euro V Motor Vehicle Fuels - As from 1 July 2010, we have tightened the statutory motor vehicle diesel and unleaded petrol specifications to Euro V level. The major difference between Euro IV and Euro V motor vehicle fuels (both diesel and petrol) is the tightening of the cap on sulphur content from 0.005% to 0.001%.

Cleaner alternatives to diesel

Taxis - To encourage a quick switch of the 18,000 diesel taxis to environmentally-cleaner vehicles, the government provided a one-off grant of $40,000 for each replacement of diesel taxis with one that operates on liquefied petroleum gas (LPG) in a subsidy programme starting in August 2000. The programme was completed at the end of 2003. Nearly all (about 99.9%) taxis had switched to LPG. 

Photo of refuelling LPG taxi Logo of LPG vehicle

Light Buses -  We started a programme in August 2002 to offer incentives to encourage the early replacement of the 6000 diesel light buses with LPG or electric ones. For diesel public light buses, we offered a one-off grant of $60,000 or $80,000 for each diesel public light bus that was replaced with an LPG or electric one respectively; for diesel private light buses, each replacement LPG vehicle was exempted from the first registration tax. At present, electric vehicles are exempted from first registration tax. The programme was completed at the end of 2005. Right now, about 60% of the registered public light buses are LPG.

Photo of LPG public light bus

         LPG Light Bus

Photo of electric public light bus

            Electric Light Bus


Controlling emissions from the remaining diesels



 Particulate reduction devices for pre-Euro light diesel vehicles

Light diesel vehicles - A programme to help owners of pre-Euro light diesel vehicles to retrofit their vehicles with particulate traps or catalytic converters was completed in 2001. More than 80% of the fleet, or 24,000 light diesel vehicles, were fitted with these devices under the retrofit programme. A particulate trap/catalytic converter can cut particulates emission from a pre-Euro light diesel vehicle by about 30%. From December 2003, a regulation requiring all pre-Euro diesel light vehicles up to 4 tonnes to be installed with suitable particulate reduction devices has been implemented.

Photo of heavy diesel vehicle

Medium and heavy diesel vehicles - A programme to help owners of pre-Euro heavy diesel, other than those heavy duty vehicles that require the operation of on-board equipment during idling (i.e. long idling vehicles) which were retrofitted separately in another programme, to retrofit their vehicles with catalytic converters was completed in 2004. More than 96% of the fleet, or 34,000 heavy diesel vehicles, were fitted with catalytic converters under the retrofit programme. A catalytic converter can cut particulates emission from a pre-Euro heavy diesel vehicle by about 25% to 35%. From April 2006, a regulation requiring all these pre-Euro heavy diesel vehicles to be installed with suitable particulate reduction devices has been implemented.

A similar programme to help owners of long idling pre-Euro heavy diesel vehicles (i.e. concrete mixer, gully emptier, lorry crane and pressure tanker) to retrofit their vehicles with catalytic converters was completed in 2005. About 95% of the fleet, or 2,500 long idling pre-Euro heavy diesel vehicles, were fitted with catalytic converters under the retrofit programme. From April 2007, a regulation requiring all these long idling pre-Euro heavy diesel vehicles to be installed with suitable particulate reduction devices has been implemented.

Photo of bus retrofitted with catalytic converter (rear view)Photo of bus retrofitted with catalytic converter (side view)

Buses - The bus companies have retrofitted about 2,000 older buses of pre-Euro or Euro 1 models with diesel catalytic converter.

Diesel Particulate Filter (DPF) - Franchised bus companies are retrofitting DPFs to their Euro II and III buses. A DPF can reduce particulate emissions from diesel vehicles by over 80%.

Strengthening emission inspection and enforcement

Controlling smoky vehicles
Photo of dynamometer smoke testThe Environmental Protection Department operates a Smoky Vehicle Control Programme that requires smoky vehicles spotted by accredited spotters to undergo a smoke test within a specified period. Failure to pass the test will result in the vehicle licence being cancelled. More than 21,000 vehicle licence cancellations have been recommended since the implementation of the programme in 1988.

To enhance the effectiveness of the Smoky Vehicle Control Programme, we introduced an  advanced emission test: the dynamometer smoke test - for diesel vehicles up to 5.5 tonnes in September 1999. Since the dynamometer test proved to be a more effective smoke testing method, it was extended to all diesel vehicles in December 2000.

Photo of joint police road-side operation

The Police supports the action to control smoky vehicles by mounting roadside smoke-testing operations. Police officers will stop vehicles having excessive emissions on road for a smoke test using a portable smokemeter. Fixed penalty ticket will be issued to the owners of vehicles failing the smoke test. The fixed penalty for smoky vehicle was raised from $450 to $1,000 on 1 December 2000.





Petrol and LPG vehicle emission checks - Since November 2000, all petrol and LPG vehicles have been required to undergo an emission check during their annual roadworthiness test.

Promoting better vehicle maintenance and eco-driving

Training and seminars on vehicle maintenance
Since August 1999, the Environmental Protection Department, in collaboration with the Vocational Training Council and Hong Kong Productivity Council had been offering training sessions for vehicle mechanics on proper engine repair and maintenance to reduce smoke emissions from diesel vehicles. At present, vehicle maintenance courses are still being offered by Vocational Training Council for vehicle mechanics.

As LPG vehicles are relatively new in Hong Kong, seminars are also organised to promote the awareness of their owners on their maintenance.

Seminars on eco-driving
Environmental Protection Department, in collaboration with the Vocational Training Council, Hong Kong Productivity Council and some relevant trade associations / institutions, conducted eco-driving seminars for the public. These seminars aim at promoting proper vehicle maintenance and eco-driving practices for fleet operators, commercial vehicle drivers and vehicle owners and drivers with a view to reducing vehicular emissions and hence improving the  roadside air quality. We shall continue to organize such eco-driving seminars.

Roadside air quality trends

The above measures have brought some improvements in roadside air quality. Compared with 1999, the roadside concentrations of some of the major air pollutants have dropped in 2011: respirable suspended particulates (RSP), sulphur dioxide (SO2) and nitrogen oxides (NOx), have been down by 33%, 56% and 28% respectively, and the number of smoky vehicles spotted has also been reduced by about 80%.

However, nitrogen dioxide (NO2) at the roadside has increased by 23% during the same period. The rise in roadside NO2 levels has resulted in an increase in the number of days with roadside air pollution index (API) reaching the “very high” level (API exceeding 100) in recent years.

Number of days with API exceeding 100
To further improve roadside air quality and tackle the NO2 problem, we have embarked on additional vehicle emission control measures. We have commenced a trial of retrofitting Euro II and III franchised buses with selective catalytic reduction (SCR) devices, which, together with the diesel particulate filters already installed in these buses, could upgrade their emission performance to the level of Euro IV or V buses. Subject to satisfactory trial results, the Government will fund the full cost of retrofitting Euro II and III franchised buses with SCR devices. We have also set up a $300 million Pilot Green Transport Fund to support the testing of green and innovative transport technologies applicable to the public transport sector and goods vehicles. In addition, the Government is consulting stakeholders about a proposal to strengthen the control of emission from petrol and LPG vehicles including the use of roadside remote sensing equipment and chassis dynamometer testing.

Building a local vehicle emission database and introducing in-use compliance program

We also seek to build up a local in-use vehicle emission database by portable emission measuring systems (PEMS) that can account for the emission design standards, operating conditions and engine conditions of local vehicles. With the database, we shall be able to estimate with greater precision motor vehicle emissions and better understand how different emission control measures will affect local emissions. Conducting vehicle emission measurements by PEMS is considered worldwide to be the most effective. We also use PEMS to develop and make preparations for introducing an in-use compliance programme, which will form part of the Euro VI vehicle emission standard to be adopted by EU in 2013. PEMS are considered an effective means of in-use compliance checking. So far, we have conducted vehicle emission measurements for about 30 in-use vehicles of various vehicle classes, like petrol cars, taxis, light and heavy goods vehicles and public light buses.

Photo of the PEMS installation on and measurements of a heavy-duty vehiclePhoto of the PEMS installation on and measurements of a heavy-duty vehicle

The PEMS installation on and measurements of a heavy-duty vehicle




Photo of catalytic converter

Photo of particulate trap

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Wednesday, 16 January, 2013