Urban air pollution

Fossi fuel use for transport has increased dramatically over the past three decades. There has been a 3% annual growth rate in the world vehicle fleet leading, in 1996, to some 800 million vehicles on the world's roads. This growth rate is faster than that of either the world population or economy. For example, in 1965 there were fewer than 60 vehicles per 1,000 people in the world; today there are more than 140.

Transportation is a major cause of air pollution in urban areas. The major air pollution concerns are carbon monoxide (CO) emissions, photochemical smog, toxic emissions, and particulate emissions. Given the high growth rates of vehicle fleets in many developing countries, vehicle-generated environmental problems have the potential to increase steadily over the next decade. Vehicles can have a significant effect on human exposure to pollutants, because their emissions are released close to the ground. For example, vehicles are the dominant source of CO emissions and are likely to contribute to high CO concentrations at street level. At moderate concentrations, CO impairs motor skills and at higher concentrations it significantly impairs the bloodstream's oxygen-carrying capacity. Emissions of benzene, a carcinogenic compound that makes up 1-to- 2% of gasoline by weight, is a major concern. It is given off as a vapor by hot engines and fuel tanks and is present in auto exhausts, partly from the combustion of other aromatic compounds in gasoline.

Particulate pollution, which has been linked to pulmonary diseases and lung cancer, has become the leading public health concern relating to urban air pollution. The relatively high particulate emission levels from diesel engines, the relatively large diesel shares in the motor vehicle populations, and the rapidly growing demand for urban transportation in developing countries indicates that this situation is likely to get much worse unless fundamental changes can be made in the transport system. Exposure to PM10 (particles under 10 microns in diameter) is associated with cardiovascular disease, chronic bronchitis, and upper and lower respiratory tract infections.

Another particularly dangerous air pollutant is lead in gasoline, a highly toxic octane-boosting additive that affects mental development in children and causes kidney damage in both children and adults. Lead is still widely used in many parts of the world, although its use has been largely phased out in many countries both because of its toxicity and because its presence in gasoline makes it impossible to use catalytic converters for controlling tailpipe emissions. Developing countries tend to suffer more, not only because of less stringent environmental standards and weaker enforcement, but also because urbanisation trends are largest in these countries.

Additionally, vehicles contribute to the formation of secondary (photochemical) pollutants, such as ozone and other oxidising agents, which are becoming a widespread urban problem. At high concentrations, ozone impairs breathing capacity, causes eye irritation, and damages materials, vegetation, and crops. Photochemical smog is especially serious in Buenos Aires, Los Angeles, Mexico City, Sao Paulo, and Tokyo and is likely to become an ever more serious problem if current trends in urban transportation persist.

Considering six indicators of air quality: sulfur dioxide, solid particulate matter, lead, carbon monoxide, nitrous oxide, and ozone, the air pollution situation in twenty megacities - sixteen of which are in developing countries - is such that 38% of the indicators register as either "serious problems" or "moderate to heavy pollution" (see figure 5). In fact, most developing country megacities have air pollution levels well above WHO guidelines, and the situation is getting worse. World-wide, air pollution (due to transportation as well as other forms of producing or using energy) is estimated to cause more than 500,000 premature deaths and millions of respiratory illnesses each year. In some countries, where cities are often cloaked in smog, the cost of local air pollution has been estimated at between 0.5% and 2.5% of GDP and as much as 5% of GDP in China (World Bank, 1997).

The poor may be exposed to higher levels of pollution due to transportation, even if they are not the primary users of transportation services, simply because they live or work in close proximity to street traffic. For instance, women working in the informal sector on Bangkok streets have high exposures to traffic-based lead emissions from gasoline fuels and have given birth to newborns with dangerously high blood lead levels as a result [REF].

Climate Change

In 1995, the Intergovernmental Panel on Climate Change (IPCC), a panel of experts assembled by the United Nations, concluded after detailed scientific reviews that "the balance of evidence suggests a discernible human influence on global climate." (IPCC, 1996). This human influence on the climate is mainly due to the emissions of three greenhouse gases (GHG) - carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O), of which CO2 is the most significant. Energy production and use is responsible for 80% of all anthropogenic GHG emissions and even in fairly optimistic scenarios, carbon emissions from burning fossil fuels (in the form of CO2) are predicted to increase quite dramatically. Indeed, according to the most likely IPCC scenarios, they will double from a total of 6.5 Gigatons of carbon today to 13.8 Gigatons by 2050 (IPCC. 1992). Current patterns of land-use and energy have been deemed responsible for the net atmospheric increases in greenhouse gases, which are predicted to result in moderate to severe changes in regional and global temperature, precipitation, soil moisture and sea level.

Figure 5 Air Pollution in Megacities of the World

Source: UNEP/WHO, 1992

Changes in temperature and water availability will particularly affect the ecosystems of tropical forests and mountainous regions, reduce soil stability in some areas, increase the stress on fisheries and harm wetlands. In turn, there could be further reductions in natural water availability in areas already under stress. There are also likely to be adverse impacts on human health due to increased exposure to very hot weather and to severe weather events, increased risk of transmission of vector-borne and contagious diseases, and possible impairments in nutritional status. Some of the most catastrophic impacts are expected to be increased hurricane intensities in areas already prone to hurricane damage, which happen to fall across many parts of the developing world, including south and south-east Asia, the south Pacific and the Caribbean. In addition, rising sea-levels and increases in flooding, coastal erosion and storm frequency or intensity will put tens of millions of people at risk, especially in island states and low-lying countries such as the Maldives, Egypt and Bangladesh. People living in poverty are likely to be the worst affected by all these impacts, because they typically lack the resources required to make even marginal allowances (such as purchasing insurance) for increases in generalised risk to human health and habitat. Significantly, the impacts of the warming are likely to lead to higher economic costs for developing countries than for industrialised countries. Warming of 2-to-3 degrees Celsius by 2100 has been estimated to cost developing countries 5-to-9% of their GDP (IPCC, 1996).