Population exposure to Particulate Matter (PM) pollution: PM10 & PM2.5 yearly and daily limits

Figure 1: Combined rural and urban concentration map of PM10 – 36th highest daily average values, year 2010 (from European air quality maps   ETC/ACM Technical Paper - Jan Horálek & al. March 2013)

The Figure above is showing that around 20% of European population had been exposed in 2010 for more than 35 days to Particulate matter (PM10) daily concentration greater than 50μg/m3 (red or brownish squares): Albany, Cyprus, Greece, Macedonia, Norway and Poland being  particularly concerned. 

Whereas during the same period, around 5% only of the same population had been exposed to yearly average concentration greater than 40μg/m3.

Why such a discrepancy between those two figures? Which either from daily or yearly PM10 concentration is more representative? How can we derive area concentration from specific measure in a station? How is defined the population exposure?

Those are the relevant question concerning PM air pollution that we want to address is the following posts.

PM is referring to a heterogeneous mixture of particles (solid and liquid) suspended in air, also known as atmospheric aerosols. PM mixture size and chemical composition change in time and space, depending on emission sources, atmospheric and weather conditions.     

PM originate partly from human or natural sources, partly from in situ or distance locations. The largest particles of concern are 10 microns or smaller in diameter (PM10). But the groups of most concern are 2.5 microns or smaller in diameter (PM2.5). The coarse particles are those which size are greater than 2.5 microns and smaller than 10 microns.

This post concentrates on PM pollutant only as currently done by the scientific community, although we are exposed to a complex mixture of pollutants. But additional research is needed to understand and quantify the possible additive, synergetic or antagonistic effects between pollutants which are encountered simultaneously in the ambient air.

Sources of PM and their effects on health, environment and climate

PM sources 

PM in the atmosphere originates from primary particles emitted directly & secondary particles produced as a result of chemical reactions involving so-called PM volatile organic compounds (VOC).

Although the influence of emission sources on PM concentration is greatest near the sources, PM concentrations are influenced by atmospheric transport between countries. In Southeast Asia, haze spell are observed in Malaysia and Singapore generated during the dry season from open fires in Sumatra (see my posts dated 15 July 2013 & 14 Sep 2012). 

Studies have shown that dust aerosols from Asia Northeastern Taklimakan, Gobi & Badain Jaran deserts and the Loess Plateau are transported to vast downwind areas including large portions of China, Korean Peninsula, Japan , North Pacific, North America , and even the Arctic regions (see Studies on a severe dust storm in East Asia by Wiao-Xian Huang & al., 2012) .

Health effects 

Some PM are small enough to pass from the lung into the bloodstream just like oxygen molecules. Then they might cause or aggravate cardiovascular and lung diseases, heart attacks and arrhythmias, affect the central nervous system, the reproductive system and cause cancer. The outcome can be premature death.

Environmental effects

PM affect animals in the same way as humans. Dust aerosol lifted into atmosphere and deposited to oceans can affect global biogeochemical cycles as well as human health. They affect plant growth and ecosystem processes, cause damage to buildings and reduced visibility.

Climate effects

PM climate effect varies depending on particle size and composition: some might lead to net cooling (white PM), while others (brown or black) to warming. Can lead to changed rainfall patterns. Deposition can lead to changes in surface albedo.

PM limit standards for PM10 and PM2.5

The following Figure 2  is summing up important existing standards for both PM10 and PM2.5.  

Limit concentrations may refer to both yearly and daily averages.  

Figure 2: Air quality standards or PM limit values to avoid health issues

A 24-hour exceedance limit applies to the 90.4^th percentile (cf. EU-PM10), which means that PM10 may be greater than 50μg/m3 but less than 35 exceedance days (9.6%) over a year. Or that the 36th highest daily average value is smaller than 50μg/m3 (cf. Figure 1 above).
    

The World Health Organization (WHO) air quality limits, shown in the above table, are stricter than the EU air quality standards. The WHO explains that it is necessary to achieve the lowest concentrations possible, because no threshold for PM has been identified below which no damage to health is observed.

To reduce issues due to the cumulative effect of PM breathing on human health, the total exposure days to a relatively small PM concentration limit is more relevant than the yearly average.

Relation between daily and yearly PM concentration

A log-normal distribution is a variable distribution whose logarithm is normally distributed.  A log-normal distribution law is used to describe random variable taking only positive values in all fields of science such as: latency periods of diseases, species’ abundancy, financial asset values, geological data, fruit and flower rises etc... These distributions follow a geometric Brownian motion with constant drift and volatility.

The measured daily average PM10 concentrations in a specific station during one year is also log-normally  distributed as seen in the following Figure 3 (see “Relation between daily exceedance and yearly averages for PM10”, Joost Wesseling &al., 2011).

Figure 3: An example of an individual concentration distribution of measured daily average PM10 concentrations in 2006 at a rural station in the Netherlands (from Joost Wesseling and alias 2011).

The two parameters μ (location) and σ (scale) determine the shape of the distribution. However, in a large number of cases, a shift (δ) (to the right) is necessary in order to satisfactorily describe the measured concentration distributions, as there is always a certain background concentration present.

Using the assumed log-normal distribution, the fraction of exceedance days having concentrations above 50μg/m3 less than 35 days over one year can be computed by integrating this curve distribution. In the curve Figure 4, this condition is met when Yearly PM10 is 31μg/m3.

If we want to have concentration above 150μg/m3 less than 1 day over 3 years (cf. Figure 1 USA PM10 standards), with same σ and σ that in Figure, this condition is met when Yearly PM10 is 35μg/m3.

Figure 4: Relation between the measured yearly average PM10 concentration and the number of days having average concentrations above 50 μg/m3. The curve labeled   is a lognormal curve with   δ=6 μg/m3 and σ=0.56.

The agreement is quite satisfactory with a ±5% confidence interval. Around 35 exceedance days per year, 5% amounts to an average underestimation of 1.75 days.So we can see that the daily limitation of PM10>50μg/m3 only 35 days per year is more stringent that EU yearly limitation (40μg/m3) but less tight than the WHO limit (20μg/m3) for two reasons: the shape of the lognormal curve and the value of the confidence interval.

For the distribution given above, the EU condition PM10<50μg/m3 up to the 90.4th percentile over 1 year (ou PM> 50μg/m3 only 35 days per year) is roughly equivalent to the USA condition PM10<150μg/m3 up to the 99.9th percentile over 3 years  (or PM10>150μg/m3 only 1 day per 3 years). If we look at the number of days- with log normal distributions having same sigma, delta as in the curve above- but variable yearly PM10: the 2 concentration day EU & US limits need  a yearly  PM10 in the range 31-35μg/m3, with EU limit being lightly more stringent to meet (yearly=31μg/m3) than  US limit (yearly =35μg/m3).

APi & PSI air quality indexes don't tell the whole truth due to very fine particulate matter missing from pollution readings

Figure 1 Jun 29, 2013: People wear face masks on Orchard Road in Singapore (fromAFP)

In our last post we have been discussing about the last Sumatra haze spell in South Peninsular Malaysia and in Simgapore, based on the official readings released by both Malaysia DOE and Singapore NEA. 

We explained that air pollution indexes and sub-indexes in Malaysia or Singapore were established following rules very similar to the US Air Quality Index including 5 only among the US AQI pollutants (PM10, O3, CO, SO2 & NO2), but without the 6^th  PM2.5 pollutant used also in US AQI and EU CAQI indexes.

In Malaysia, it seems that PM2.5 is some time measured but not published, while in Singapore PM2.5 is measured and published along with the PSI index, but not incorporated as a sub-index before air quality index computing. 

Air Quality Index compared computations from EU, US, Malaysia and Singapore

In my post date 14 July, 2013, I have explained how is computed the US AQI Index. You may find the AQI and its sub-indexes definition in « Technical Assistance document for the Reporting of Daily Air Quality the AirQuality Index (AQI)”.

In UE the Common Air Quality Index (CAQI) is an European Development with two indexes « background » and « road-side ». We have selected as a comparison’s reference the background CAQI and its sub-indexes see CAQI from EU Common Air Quality Index European Development.

Because CAQI is aiming mostly light polluted areas, the EU pollutant scale is much more limited than in US AQI and as a consequence the grid values are much higher (for instance CAQI=100  with PM10=100 when US AQI= 100 with PM10=154). So we have adjusted and decreased the CAQI grid in order to meet US AQI at least for PM10.

For Malaysia API: see “API a guide for air pollutant index in Malaysia” and for Singapore PSI  index: see “Computation of the PollutantStandards Index (PSI) “PDF document.

The following five Figures 2-6 are giving, for any value of the measured pollutant concentration located inside two "turning points", the successive linear relationships to calculate the value of the index with a "grid" common understanding between all indexes and sub-indexes. 

Each broken line describes pollutant action on human health, each turning point corresponding to the crossing of a threshold effect on health. The greater the index the more unheathy it is with grid<100 corresponding to good or moderate air quality. 

Figure 2 shows a good relationship between all the various sub-indexes for PM10  sub-indexes; and a slight divergence between EU and US for PM2.5 sub-indexes.

Figure 2: Comparison of air quality sub-indexes for particulate matter pollutants (PM10 & PM2.5), over EU, US and API/PSI South Asia sub-indexes

Figure 3 is showing a good relationship between US, Malaysia and Singapore for CO sub-indexes. Inversely EU index is quite different with a much higher value for the pollutant concentration.

Figure 3 : Comparison of air quality sub-indexes for carbon monoxide (CO) pollutant, over EU, US and API/PSI South Asia sub-indexes

Figures 4, 5 & 6 are showing more divergences between all countries for O3, SO2 and NO2 pollutant sub-indexes.

Figure 4 : Comparison of air quality sub-indexes for Ozone pollutant (O3), over EU, US and API/PSI South Asia sub-indexes.

Figure 5 Comparison of air quality sub-indexes for Sulfur Dioxide pollutant (NO2), over EU, US and API/PSI South Asia sub-indexes

Figure 6 :  Comparison of air quality sub-indexes for Nitrogen Dioxide pollutant (NO2), over EU, US and API/PSI South Asia sub-indexes

The importance of PM2.5 pollutant to assess the air quality 

(See PM2.5 fact from  US EPA)

Particles less than 10 µm in diameter (PM10) pose a health concern because they can be inhaled, accumulated in the lungs and damage the respiratory system.

Particles less than 2.5 µm in diameter (PM2.5) -referred to as "fine" particulate matter- are believed to pose the greatest health risks. Why?  Because of their small size (around 1/30th the width of a human hair), fine particles can be trapped deeply into the lung cells producing various health hazards: asthmas, infection, cancer etc..

Sources of fine particles include ashes and residues from all types of combustion activities (wood burning, power plants, motor vehicles etc.) and certain industrial processes.

Particles with diameters between 2.5 and 10 µm are referred to as "coarse" particulate matter. Sources of coarse particles include crushing or grinding operations, and dust from paved or unpaved roads.

Other particles may be formed in the air from the chemical change of gases. They are indirectly formed when gases from burning fuels react with sunlight and water vapor. These can result from fuel combustion in motor vehicles, at power plants, and in other industrial processes.

A study for Air Pollution Effects published by "The Lancet" in July 2013 assessed air pollution for particulate matter with diameter of less than 10 μm (PM10) & less than 2·5 μm (PM2·5). It shows that exposure of population to particulate matter air pollution even at concentrations below the existing EU air quality limit values for PM10 (40 μg/m³) and PM2·5 (25 μg/m³) might increase the risk for lung cancer.These EU air quality limit values are associated with API/PSI = 50 in Figure 2. 

Roughly one out of three persons is at a higher risk of experiencng PM2.5 related health effects, mostly children with their bodies still developing and the elderly due to their lower resistance. 

People of all age active outdoors during physical activities are at increased risk because with increased air intake PM2.5 penetrate deeper into the more vulnerable part of the lungs.  

Due to their deadly effect on human health it is urgent - as for EU and US- to include PM2.5 in the sub-index standards in Southeast Asia API/PSI readings

As we know that most API/PSI readings are mostly derived from the high value of PM10 sub-index, they have reciprocally the same "turning points" and  it is easy to derive the value of PM10 from the API/PSI readings by using the PSI/API sub-index reciprocal linear relationship.

The following Figure 7 gives both values of PM10 and PM2.5 concentrations respectively computed or read for South Singapore PSI (See: PSIHistorical readings).

We can see that PM10 is mostly composed of 75-80% of PM2.5. This means that the coarse particulate are only 20-25% and - as we can see on Figure 2 above- that the value of the PM2.5 sub-index is much higher than the value of the PM10 sub-index.

Figure 7 : South Singapore PM10 & PM2.5 concentrations computed from PSI or read

The following Figure 8 shows that the “true” PSI - including the PM2.5 sub-index -is around 50-80% higher than the official reading.   

Figure 8 : South Singapore official PSI without PM2.5 and PSI including PM2.5 sub-index  

On 20 -21 June 2013, the “official” PSI as recorded by Singapore NEA was only 246 but the "true value" of the Pollutant Standards Index incorporating the more dangerous PM2.5 pollution was around 344. 

However, it appears that in its communication with the media, Singapore NEA has already made ​​the change, according to an article in the Straits Times referring that Singapore Pollutant Standards Index "soared to 321 on 19 June the worst reading in its history, the previous being 226 in 1997".

If we keep in mind that at the same time in Malaysia the highest readings - 746 in Muar, 487 in Ipoh and 443 in Melaka- were issued without any correction for PM2.5, the general picture on the Southeast Asia pollution was reallly difficult to assess!    

So in order to inform as fairly as possible the population on Air Pollution  health hazards, there is a urgent need to clarify this issue by incorporation-as in EU and US-  the PM2.5 fine particulate matter sub-indexes into API / PSI air quality indexes used in Southeast Asia. 

Sumatra haze becoming a yearly recurring event with growing pollution level?

Figure 1 : On Saturday, June 22, 2013, motorists make their way through a town covered with a thick haze in Muar. FILE PHOTO: AP

In South Peninsular Malaysia and Singapore island, the last Sumatra’s smoke haze spell – 23 days from 10 June to 2 July 2013- was definitely more serious than the last year occurrence, while haze’s pollution could still return anytime during the coming months.  

A huge amount of information was published by various media during this period. But sometimes the true meaning of air pollution information issued and their outcome in terms of public health were difficult to understand and - to say it bluntly- a little hazy!

We would like to return on this period and look at all data issued on air quality by Department of Environment (DOE) in Malaysia, National Environment Agency (EPA) in Singapore and ASEAN Specialised Meteorological Centre (ASMC).

How are established both Air Pollution Index (API) in Malaysia and Pollutant Standards Index (PSI) in Singapore?

All figures concerning air pollution index and sub-indices in Malaysia or Singapore are established following rules very similar to the US Air Quality Index  (see AQI Technical Assistance document for the Reporting of the Air Quality Index AQI).

For the US AQI, first specific sub-indexes are separately computed concerning the 6 following pollutants:

(1)- Particulate matter smaller than 10µm (PM10 ),

(1bis)- Particulate matter smaller than 2.5µm (PM2.5),

(2)- Ozone (O3),

(3)- Carbon monoxide (CO),

(4)- Sulfur dioxide (SO2) ,

(5)- Nitrogen dioxide (NO2) .

For each pollutant a common “grid” of communication relationship is introduced, with a growing scale grid and associated pollution level where: 0-50 is a “good air quality”, 51-100  is a pollution “moderate”, 101-150 a pollution  “unhealthy for specific groups”, 151-200  is a pollution ”Unhealthy”, 201-300  is “very unhealthy”, and 301-500 is “Hazardous”.

Then each sub-index is computed and the highest sub-index value is the US AQI value for the location and the time concerned.

The only difference concerning Malaysia’s API and Singapore’s PSI in relation with US AQI is the PM2.5 pollutant. 

In fact (1)) and (1bis) pollutants are closely interrelated because particulate matter smaller than 2.5µm are also smaller than 10µm. However PM2.5 are also much more unhealthy and as such should have a higher “grid” value!

In the case of Malaysia, PM2.5 seems to be measured but is not published.

In the case of Singapore , PM2.5 is measured and published with the PSI index.

API & PSI values are computed based on the average concentrations of air pollutants PM10, O3, CO, SO2 and NO2 expressed in µg/m3 or in ppm. The average time period is pollutant specific: daily for PM, 8h for CO, hourly O3, SO2 and  NO2.  

During the haze spell in Malaysia the PM10 sub-index value due to the high PM10 concentration is the highest compared with the other pollutants and this determines the API readings.

Nevertheless by the late afternoon or early evening, usually ozone concentration is high and dominates the API readings in some areas. Under the sunlight influence, nitrogen dioxide and volatile organic compounds emitted from motor vehicle exhaust and industry react to form ozone in the earth's surface.    

            

Peninsular Malaysia was more severely affected than Singapore

In both countries the monitored pollutants and sub-indexes are the same and so the comparison is meaningful. 

The following Figures 2 & 3 give the API readings in Malaysia:

Figure 2 : API index from 22 June to 2 July 2013 on 11 locations in Johor, Malaka, N. Sembilan and South Pahang  (see DOE Malaysia)

Johor (Kota Tinggi, Larkin Lama, Muar, Pasir Gudang ), Melaka (Bandaraya, Bukit Rambai) and Negeri Sembilan (Port Dickson)  were especially polluted with the highest API reading  ever seen in Johor Muar (756 API on 23 June), as explained my Malaysian Environment Minister in Asia Pacific Channel News.

Figure 3 : API index reading on 13 locations in Perak, Selangor, Kuala Lumpur  and Terengganu (see DOE Malaysia)

Selangor (Banting , Pelabuhan Kelang) and  Terengganu (Kemaman) were especially polluted with the highest reading in Selangor Pelabuhan Kelang (487  API on 27 June).

The Figure 4 gives the PSI reading in Singapore:

Figure 4 : PSI readings on 5 locations in Singapore (see NEA Singapore) 

Generally speaking, Singapore was less polluted than Malaysia: around 5500 cumulated readings unhealthy for special group on 23 days (at 7am, 12am, 4pm) compared to 7500 cumulated reading in Malaysia during the same period (7am, 11am, 5pm).  

South Singapore was especially polluted, with the reading (PSI=246 on 22 June). The highest points in Peninsular Malaysia being 400-700.

So if we take off the "good readings" and look also at the highest readings, Malaysia was at least "twice more polluted" than Singapore during this haze spell.

Moreover the 2013 haze spell (in June and up to 15 July) was much more severe than 2012 June and July occurrence,  but with a hotspot count very similar

Compared to the 2012 June & July haze in Malaysia: the spell is much stronger and only located on South peninsular Malaysia .

In 2012 there was a 4000 cumulated reading (at 7am, 11am, 5am) and the maximum readings were in Sarawak (API=247 on 27 June 2012), Selangor  (API=147 on 15 June 2012), with Penang having a 5 day haze spell (API=105 on 20 June 2012).

In 2012, the cumulative hotspot count for Sumatra while being among the 2 highest of the last 8 years is in line with last year count progression (see following Figures 5, 6 & 7).  

So the haze in becoming more or less a yearly recurring hazard with pollution growing each year!

Figure 5 : Cumulative hotspot count for Sumatra detected in the ASEAN region for 2006 to 30th June 2013; the counts are based on the hotspots detected by the NOAA-18 Satellite

In Sumatra  the open burning areas seemed to be more located over the Riau Province  in Central Sumatra,  while last year the hot spots were coming up to Kualuh Hilir in North Sumatra.  

This combined by the direction of winds have kept the Northern states of Perak and Pulau Penang  less affected.

The international uproar have been so severe – especially from Singapore- that the Indonesian Government had announced its decision to ratify the“2002 Asean Treaty on Transboundary Haze Pollution signed by all 9 other ASEAN countries.  

Figure 6 : Regional haze map on 21 June 2013 

Figure 7 : Regional haze map on 23 June 2013

Two or three wheeled Motorcycles are a major issue for congestion, pollution and road safety in most Asia’s cities

Figure 1 : A family riding a motorcycle in Cambodia 

Two and three wheeled motorcycles are mostly located in Asia and used for private household mobility or public transport

In 2010, the current worldwide motorcycle populaton was around 450mil, on which 77% was located in Asia Pacific, 8% in both Europe and America, 4% in Middle East & Central Asia and only 3% in Africa. 

During the past period 2002-2010, the worldwide fleet increased annually by 9.5%. As we can see in Figure 2, the biggest increases of the motorcycle stock by region were South America, Asia Pacific, while Africa, Middle East, North America and  West Europe were lagging behind.

Figure 2: Evolution of 2-3 wheeler stocks over worldwide regions 

In emerging and developing countries, 2-3 wheelers are mostly cheap mode of transport used for household mobility with low or medium power mopeds, motorcycles and scooters (<150cc).

For developed countries –especially in North America-  it is more a recreational vehicle with higher power capacity (500cc and more).

In 2010, the 10 highest worldwide 2-3 wheelers rate ownership were located mainly in Asian countries (see Figure 3): Taiwan (642 units for 1,000 people), Vietnam (362), Malaysia (332) and Indonesia/Thailand (251), the others being Uruguay, Italy, Dominican Republic and Lao (130-280).

China (77) and India (68) were ranking only the 22^nd and 26^th with Japan 27^th (65) together with 4 European countries, Brazil and Colombia. 

Figure 3: The first 2-3 wheeler stocks and ownership rates over worldwide regions (2010 figures from WHO road safety 2013)

But due to their higher populations among the 10 biggest worldwide motorcycle stocks in 2010 we find 8 Asian Pacific countries.

Among the first 5 biggest, 3 countries China, Indonesia and Vietnam have registered very high stock increases over the last 8 years around 15-30% annually ( see Figure 4).

Figure 4 : Evolution of the biggest 2-3 wheelers stocks in 2010 over worldwide regions (2002 figures from Worldmapper)

Why are 2 & 3 wheeled motorcycles so prevalent inside Asian Pacific mobility modes ?

Motor vehicles due to their low initial cost overwhelmingly dominate the market for ground mobility of passengers and freight in developing countries. Bus lines, trains and rapid transit systems in urban areas are less frequent than what exists in developed countries.

Moreover inside the developing countries’ motor vehicle market: mopeds, 2-3 wheelers or scooters have the lion's share as compared to 4 wheelers passenger cars, light and heavy trucks or bus.

There is a strong upfront advantage in term of cost....:

The basic advantage is cost efficiency and lower weight especially with two-stroke engines delivering high torque and greater power output at a very low cost.

In India during 2011, the range of prices of motorcycles of 75-125 cc category – the highest selling category – was around 48,500 Rs (850$) and for 125-250 cc around 81,500 Rs(1,300$) (see Narayan V. Iyer, August,2012).

As concerns congestion, two or three wheelers offer high maneuverability at a low speed, in narrow lanes & crowded urbazined areas, not to mention the need of smaller parking areas. 

Moreover in Taiwan, Europe and Malaysia - as we can see today in congested Penang Island- there is a surge of two wheelers among car owners as an additionally mode of mobility.

Concerning the issue of 3-wheelers reducing urban congestion maybe is it questionable. For instance in Bangkok the traffic at peak hour could really become chaotic. There is a need to rationalize organization of road and intersection designs with the ban of three wheelers from highways!

....But afterwards there are huge recurrent pollution externalities:

There are higher pollutions by excessive hydrocarbons (HC) and  particulate matter (PM)) emissions from two-stroke engines as compared to four-stroke. Why?

The two-stroke exhaust gas is forced from the cylinder by the pressure of the incoming charge. A significant part –around 20-30%- of the fresh charge escapes unburned. This coupled with the tendency to misfire at low load results with high HC emissions.

Oil lubricant in two- stroke engines needs to be mixed in the fuel to lubricate bearing and piston and this is thus a major source of smoke and PM. Many drivers add more lubricant than necessary to protect the engine. But the pollution effect of much higher emissions far outweighs the benefit to the vehicle owner! 

The drawbacks of the two-stroke engines are even made worse when used on a 3 wheelers. Such vehicles are underpowered so the engine usually operates near wide open throttle producing huge fuel consumptions and high emissions.

As a result, motorcycle emissions from a single two stroke can exceed those of a 3 passenger cars or those from a heavy duty diesel truck! Emissions from 2 & 3 wheelers represent the most serious problems for developing cities.

Three wheelers taxis are perceived as less compliant with traffic regulations and more accident prone than 4-wheels passenger vehicles. Such motorcycle’s dependency might lead to the exclusion or more adapted public transports such as bus.  In Delhi (India), Denpasar (Bali) and Hanoi (Vietnam) less than 5% of public transport are operated by bus.

Today, the general consensus is that the limits of 2-stroke technology have largely been reached in all classes, and therefore 2012 was the dawn of a technically relevant new era, with four stroke motorcycles filling all fields of the motorcycle market.

For the two wheelers, the shift from two-stroke to four-stroke engines begun around 2000 and gained further momentum in 2005- 2010. The private user’s shift was not only to meet the emission standards but also to change to more fuel efficient 4-stroke. But in India the relative share of 2-stroke engines is still around 6% of the total powered two-wheelers sales in the country (see Narayan V. Iyer, August, 2012).

For its three-wheelers, Bajaj developed a four-stroke engine with a program to stop production of the two-stroke. Unfortunately, the four-stroke rickshaw did not receive a favorable response from the market. Bajaj, therefore, had to restart the production of the popular 2-stroke. The poor market acceptance was attributed to the profiles of three-wheeler customers who need to earn a living from the vehicle and would not take the risk of investing in a new type of vehicle, with which they are not familiar, and at a higher price too (see ibid.).

Further on, as far as the vehicle stock is concerned, the low cost of repairs and the huge cost of the renewal in developing countries leads to a very low turnover of the 2-3 wheels population which means that the  two-stroke engines recurring pollution externalities might remain still present for a long time.

2010 registered vehicles breakdown over countries

If we want to assess the motorcycle’s dependency throughout the various Asian Pacific countries, it is fascinating to look at the rate of 2-3 wheelers in relation to the passenger 4-wheeled cars.

The Figure 5 below shows ( logarithmic vertical scale) that Vietnam is far ahead of all other countries and that the cars are almost completely driven out of the country!

Malaysia is the hinging point between developing and developed countries.There is an automotive car industry with Proton and Perodua and 3-wheelers are banned for public transport. 

All countries on the left hand side from Malaysia have 3-wheelers taxis, except China and Taiwan.

Figure 5: Rate of 2-3 wheelers as compared to passenger cars in Asia Pacifiic decreasing from left to right

Figure 6: Total vehicle breakdown in 2010 by countries, decreasing income from left to right (fromWHO road safety status 2013)

Figure 7 : Vehicle breakdown per 1,000 people in 2010 by countries, decreasing income from left to right (fromWHO road safety status 2013)

Unlike the pattern for passenger cars, the ownership growth pattern for motorcycles varies greatly in different countries.

The growth of motorcycles could be influenced by three sets of factors (see "Vehicle China pollution by 2050"  Huo, Hong and al.):

(a) Economical factors: in China motorcycle ownership in household with per capita income below 2,500$ rises as per capita income increases. However, when per capita income reaches 3,000 to 3,500$, the growth rate appears to slow, reaching a saturation level. Also at this income level, car purchases begin to increase rapidly, suggesting that a switch from two wheelers to passenger cars occurs in urban families as income rises.

(b) Geographical factors: ownership tends to increase as per capita GDP grows, except in several geographically unique countries and areas, such as the Philippines, which is archipelagic, and Singapore, which is a city state. In China, because geographical features vary dramatically throughout the country, two wheelers ownership in southern regions is higher than in the northern regions because the warmer southern climate makes riding motorcycles more comfortable. 


(c) Policies: Major Chinese cities thrive to limit, and even ban, the registration and use of motorcycles in urban areas. 

Figure 8 tends to show that the motorcycle ownership's relationship against per capiat GDP is more or less hyperbolic, due to the shift from two-wheelers to passenger cars when per capita income reaches 3,500$, with the notable exception of Taiwan which is in a unique position.

Figure 8: Relation of motorcycles' ownership against per capita GDP growth (all 2-3 wheelers figures from WHO road safety report 2013, except Taiwan)  

Road safety fatalities

The overall global road traffic fatality rate worldwide is 18 per 100,000 people. However, low and middle-income countries have the highest annual road traffic fatality rates, at 18.3-20.1 per 100,000, while the rate in high-income countries is the lowest, at 8.7 per 100 000.

But in Asia Pacific countries the safety achievements are better with respectively 7.1 and 8.2 rates per 100,000 people for low & middle income or high income countries.

However the worse performing countries are Malaysia and Thailand (see Figure above). 

In low and middle Asian Pacific countries 33% of the fatalities are made to motorcyclists.

The associated cost of the DGP  lost from these fatalities is estimated to be around 3%.

Figure 9: Traffic death fatalities over Asia Pacific countries ( from WHO Road Safety 2013report)

Figure 10: Traffic death fatalities over main Asia Pacific regions (from WHO Road Safety 2013report)