Nairobi on risky path to becoming ‘urban heat island’ as taller skyscrapers block dispersal of pollutants

Clean air is a public good, said a great thinker once. Indeed, no other resource exhibits the same degree of ‘publicness’; land can be parceled and fenced off; water can be bottled; scenery can be hidden; one can even isolate himself from noise; but man has no choice but to breathe the air around him — polluted or not.

For residents of Nairobi’s southwestern zones, that statement cannot be truer. The city’s industries have been polluting air up to 100 kilometres away, according to research. And the most-at-risk populations have been not those that live within the city, but those who reside a few kilometres away, from Kangemi to Limuru and Naivasha; from Kajiado to Magadi.

In a paper presented early this month in Paris, France by a team of Kenyan scientists to a Unesco scientific conference dubbed ‘Our Common Future Under Climate Change’, researchers Victor Ongoma, George Otieno and Onyango Augustine Omondi shared the sequence of pollution from Nairobi’s industrial area to other parts of the country.

In the paper — Simulations of Pollutant Dispersal Over Nairobi City, Kenya — the researchers said that “the winds in Nairobi city are mainly easterlies, implying that the pollutants are transported... southwest and northwest of the town”.

“The transfer of pollutants is at 100 kilometres per hour,” they continued, “and therefore the city is left pollutant-free as the dust and other particles blown elsewhere.” That means that, for residents of the affected areas, the air they breathe is floating with particulate matter, a complex mixture of solid and liquid particles of organic and inorganic substances such as minerals, dust and water. Such substances, when inhaled, are associated with respiratory infections, including asthma and lung cancer, especially among the young and the elderly. The chemicals may also cause eye diseases.

The researchers’ findings seem to be in agreement with the Kenya 2014 Economic Survey, which reported that respiratory infections caused the highest number of illnesses in Kenya in 2013, with 14.8 million cases reported.

Also, according to the Nakuru Provincial General Hospital deputy medical superintendent, Dr Bernard Warui, most of the patients at the facility, some of whom come from Naivasha and surrounding environs, keep complaining of upper respiratory infections, which are linked, mainly, to air pollution.

The study, conducted between January and December 2013, showed that most of the commercial activities in Nairobi are concentrated within the city, whereas most of the industrial activities are located to the southeast.

DISPERSION OF POLLUTANTS

Mr Ongoma, a doctorate student of urbanisation meteorology in China, told the gathering in Paris that the transport and dispersion of pollutants from one locality is precipitated by wind, rainfall, air temperature and relative humidity.

However, urbanisation — the movement of people from rural to urban areas in search of economic opportunities, and which Mr Ongoma describes as “a necessary evil” — slows down wind speed due to the buildings and structures along the flow path.

“The pollutants, over time, are not properly dispersed because the wind speed is greatly reduced. Therefore, residents of upcoming cities risk living in polluted environments in the future,” said Mr Ongoma.

While the air in Nairobi might not have the same number of pollutants as those recorded in its southwesterly neighbourhoods, city dwellers are not much safer either. Increased temperatures due to energy use, vehicle emissions and dwindling tree cover are gradually leading to an “urban heat island”, which means Nairobi area has higher temperatures than the surrounding regions.

This is in turn reducing atmospheric pressure in the city, and thus affecting wind speed and, over time, trapping the pollutants within the city.

According to the study, the dispersal of pollutants is observed to be furthest during the “DJF season” (December-January-February) and “JJA”  (June-July-August).

It is least during the March-April-May and September-October-November seasons. This implies that the concentration of pollutants in the atmosphere during the city’s two rain seasons is likely to be higher than what is observed during dry and cold periods.

While there is little that can be done to stop the dispersal of pollutants all the way to Naivasha and Kajiado because the direction of wind flow is a natural phenomenon, Mr Ongoma thinks city planners and managers can do something to stop the gradual conversion of Nairobi into a heat island.

“How can they factor this information into future designs?” he asks. “Will we see new designs informed by such studies?”

The findings of their study, Mr Ongoma adds, mean that land on the western side of Nairobi should be cheaper than that on the eastern parts, because the western areas are more polluted. However, that is not the case as, despite the pollution, Nairobi’s western side is more developed, has better infrastructure, and therefore attracts higher sums per acre than the eastern regions.

Air pollution negatively impacts human health and has been proven to be dangerous even with short-term exposure. It causes wheezing, coughing, shortness of breath, phlegm and sore throat, as well as irritation of existing respiratory conditions such as asthma.

Further, dirty air causes lung damage as well as heart disease, stroke and cancer. The WHO estimates that one in eight deaths worldwide in 2013 resulted from air pollution.

About seven million people die prematurely each year from air-pollution-related infections. Of these, around 630,000 are from Africa, according to various studies. Of concern to health experts and environmental activisits is that these sources of pollution will continue to exist in the atmosphere for over 15 years before they are eliminated.

In Time to Act to Reduce Short-lived Climate Pollutants, a report by the Climate and Clean Air Coalition in conjunction with the United Nations Environment Programme, reseachers warn that air pollution is now the world’s largest single environmental health risk.

The sources of the air pollution are identified as soot and carbon (due to incomplete burning of fuel such as diesel in traffic), methane (emitted in livestock manure, waste management and rice cultivation), hydroflourocarbons (in air conditioning, refrigeration) as well as various other industrial gases that have a warming effect on climate.

Other sources include mining and cement production, which release dust and carbon dioxide to the environment.

Air pollution is also a contributor of acid rain, which has been responsible for a lot of damage to soil, fish resources and vegetation, often very far away from the source of the pollutant.

It also causes smog, which is a reduction in visibility due to scattering of light by airborne particles.