Can advance vehicle emission standards reduce PM2.5?


Despite the severe situation of the PM 2.5 dust problem was relieved according to the changing weather conditions. However, this situation still has chance to come back if the factors of causing small dust still exist. The government, hence, has prepared measures to prevent and solve problems in the medium and long term. From the results of the Source Apportionment analyzed the chemical composition of the dust in the atmosphere in interested areas by Kim Oanh (2007), PM2.5 dust found in Din Daeng area came from diesel car exhaust emission around 52%, 35% from biomass burning, and 13% from secondary dust and others. Then 10 years later, Kim Oanh (2017) found that PM 2.5 dust was derived from diesel car exhaust around 20.8-29.2%, from biomass burning 24.6-37.8%, and from secondary dust and others 15.8-20.7%.  Although the study found reduction of PM 2.5 emitted from vehicle exhaust, but it is still a crucial cause of small dust in transport sector.  The government has established policies for long-term actions, e.g. to urge B20 using in diesel vehicle, to raise up pollution standards to Euro 5 and Euro 6 standards, or to promote NGV fuel, and hybrid or electric buses, including to accelerate construction of the public transport services network to connect all systems covering Bangkok area.

In this regard, the relevant government sector has set measures to support cars that help reduce pollution, such as the Excise Department, Ministry of Finance, has brought about the PM emission factor primarily in determining tax rates in conjunction with Carbon dioxide (CO2) emission principle. Presently excise tax bases on CO2 emissions, which would help reduce greenhouse gas problems, but does not cover pollution causes by small dust and smoke.  The Office of the Board of Investment (BOI) has promoted investment in electric vehicles by reducing the excise tax on electric cars from 8% to 2%.

For upgrading the emissions standard from the vehicle's exhaust emission, from current Euro 4 standard to Euro 5 standard which was originally planned to be enforced in the year 2024, has been urge to be used faster by year 2021, and Euro 6 standard in the year after.  Such standard is expected to help reduce small sized particulate emissions from exhaust emission of new car produced. In this article, we will understand the format of the Euro 5 standard, which has the highest level at Euro 5b+ and Euro 6 that develops to the Euro 6d level, and how those could reduce pollution.

The emission standards, that have been developed to be more stringent periodically in order to comply with the environmental situation and the amount of pollution released according to fuel consuming, divided into various levels from Euro 1 to the latest Euro 6d which has been exercised since 2014. The toxin substance measured are Carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), and particulate matter (PM) in which we are paying attention to.
• In the case of cars using gasoline engines, the NOx value in Euro 5 will be reduced from Euro 4. PM measurement is added in Euro5 and above, which there is never before in Euro4. From Euro5b upward, particulate number counting is added.
• For diesel engine vehicles, the pollution adjustment is made stringent limit value of NOx, THC + NOx, and PM. Particulate counting (PN) is used from Euro 5b, same as gasoline engine vehicles.

Exhaust emission limit for passenger vehicle using gasoline and diesel engine

Exhaust emission limit for commercial vehicle using gasoline and diesel engine

The counting of particles is put into the Euro standard criteria, especially dust with size of not more than 2.5 microns, which is compared to about 1 in 25 parts of the human hair diameter. It is so small to go through human nose hair and spread into the respiratory tract, bloodstream and into other organs of body. Such small particle cannot be detected by using conventional measuring methods used for PM measurements in the EURO 4 standard. The quantity of small particles is counted by using particulate counter in nanograms unit.  The principle of particle counter is that collected dust is separated by the grain size, smaller than 2.5 µm, and sucked through heated line at 150 ° C to the Primary dilution. The large size particle will be separated and not be taken to measure.  The screened particles then go through Evaporation Tube Heated line at 350 ° C, and condensed by injecting Butanol (Alcohol) to coat pollutant particle, and then reduce temperature to less than 35 ° C in order to assemble particle into dust and count by laser beam.

Automobile exhaust emission standards must be in line with automobile fuel standards, for the efficiency of engine to generate lesser toxic emission as required. The enforcement of fuel standards must be in consistent direction with exhaust emission standards. The properties of Euro 5 fuel will reduce sulfur to 10 ppm, or 5 times reduced from Euro 4 standard, which affect the decreasing of exhaust pollutants according the standard’s requirement.

In summary, raising the level of automobile exhaust emission standards to Euro 5 and Euro 6 was aimed to expurgate cause of pollution from the origin and reduce the proportion of PM 2.5 formation in the transportation sector. From the policy to accelerate emission standards enforcement, the Ministry of Industry then plans having infrastructure to support the inspection and testing of cars produced and sold in the country, in order to meet standard requirement. And aside from helping to reduce emissions, especially the small dust, it also would increase the competitiveness of Thailand automobile industry to meet international standards, as well.


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