The number of motor vehicles and their miles driven has literally exploded over the past 60 years and the likelihood is that this growth will continue for the foreseeable future. While vehicle populations are roughly stabilizing in the highly industrialized OECD countries, they are accelerating in rapidly industrializing highly populous countries. In response to strong and aggressive regulatory programs, especially in the United States, new vehicles being sold in many countries today are much cleaner than in the past. For example, over 95% of all gasoline sold in the world today is lead free and over 95% of all new gasoline fueled cars are equipped with a three way catalyst which dramatically lowers CO, HC and NOx emissions per mile driven. As a result, air quality in urban areas in developed countries has generally improved.

However, even in the developed world, air pollution levels in major cities continue to exceed levels necessary to protect public health. And in the rapidly industrializing countries, pollution in many cities is worsening. Therefore, with regard to urban and regional pollution, two major challenges remain:

1. To accelerate the introduction of the state of the art technologies for clean vehicles and fuels in rapidly industrializing countries such as China, India and Brazil and get at least modest controls in places where none currently exist such as in much of Africa and the Middle East, and

2. To phase out or clean up the so-called legacy fleet of existing high polluting vehicles. (California, for example, has embarked on an effort to eliminate every diesel vehicle in the State not equipped with a diesel PM filter either by mandatory retrofit or scrappage.)

With regard to climate change the picture is much more bleak and the challenge more daunting. Transportation is already a large contributor to the problem and is a rapidly growing sector. Modest programs to reduce fuel consumption or greenhouse gas emissions from light duty vehicles are being phased in and California and the EU have initiated efforts to reduce the carbon content of vehicle fuels. Much more will need to be done with a likely shift to battery electric vehicles fueled by green electrons or fuel cell vehicles fueled by renewable hydrogen in future decades.

Normalized to 2000

Normalized to 2000

Fig. 6.9 Global trends in on road vehicle black carbon emissions

As efforts to reduce CO2 by 70 or 80% by 2050 receive high priority, aggressive short-term actions to reduce short-lived greenhouse pollutants hold promise. The US, Europe and Japan are phasing in high efficiency PM filters which will also reduce black carbon emissions dramatically. On a global basis, driven by these efforts, road vehicle emissions of black carbon are declining rapidly as shown in Fig. 6.9.

However, after 2025 they will start to increase unless the rapidly industrializing countries also move to require PM filters on new diesel vehicles soon. If they do, the downward trend in black carbon can continue while CO2 reduction measures are developed and implemented.

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