Sana’a trees need protection from exhaust smoke [Archives:2008/1182/Health]

August 18 2008

Tareq Al-Adil
For The Yemen Times

Yemeni environmental experts warn that widespread air pollution in the capital of Sana'a is threatening the city's plant life and roadside trees, in addition to posing negative health effects to Sana'a residents.

Ali Al-Harsh, streets and gardens observation and evaluation manager at Sana'a's General Management of Parks and Gardens, says roadside trees are greatly affected by exhaust pollution, particularly that emitted from diesel engines.

“Roadside trees in Sana'a are exposed to exhaust pollution as a result of the increasing number of vehicles. Some trees die while others are exposed to disease. Trees can only tolerate such contaminants to a certain degree and then they die,” Al-Harsh pointed out, adding, “A layer of such contaminants is visible on the tree leaves, particularly on high-traffic roads like Siteen, Yasser Arafat, Khawlan, Berlin, Hadda and Jumhury Streets.”

Abdu Al-Qadhi, director of Al-Thawra Garden, confirms that such a layer of contaminants exists on leaves, which blocks their pores and reduces the exudation process, resulting in an imbalance in their ability to take in carbon and produce oxygen. This kills trees and makes tree growth very slow.

“Trees absorb approximately three kilograms of toxic gases from vehicle exhausts every day,” Mohammed Al-Shami, Saba'een regional manager notes, adding, “You can see that flowers also are flecked and their growth also is very slow.”

According to scientific studies, plants and trees are known to be friends to the environment, as they participate in cleaning and keeping the environment free of pollution.

Through the exudation process, trees humidify the surrounding air, which balances out the temperature around the tree. They also remove poisonous and toxic gases from the air by using air currents, as well as decrease the sun's heat in the surrounding area.

Plants absorb carbon dioxide and produce oxygen daily, working like air filters and producers to balance the environment.

Diesel engines affect and damage trees the most. Moreover, sunlight in the presence of such exhaust promotes the formation of ozone gas that injures plants. Symptoms of ozone damage to plants range from slow growth to severe leaf browning, followed by premature leaf drop.

Deciduous trees that lose their leaves in the fall exhibit a stippling or flecked pattern on the upper leaf surface. These flecks can be white, tan or black, depending on the plant species.

Studies have found that some trees are resistant to exhaust pollution while others aren't. Researchers have discovered that Dalbergia sissoo and Calotropis procera are the ideal plant species to monitor lead and carbon in the air, as lead and carbon mostly come from vehicle exhaust pollution.

In an attempt to fight air pollution in the capital city, the General Management of Parks and Gardens in Sana'a intends to expand green areas on the streets. According to Al-Shami, the percentage that street trees are damaged by exhaust pollution is an important indicator in determining what type of trees should be planted on such streets.

“For instance, trees have been found to have 5 percent of this pollution, whereas flowers have from 10 percent to 15 percent. Fortunately, most plants, even those sensitive to damage, are believed to tolerate air pollution damage during their dormancy.”

Al-Shami notes that Duranta trees are particularly weak in tolerating exhaust pollution, as they die very quickly. “We noticed this when we began planting this type of tree on Taiz Street,” he said, “On the other hand, Ficus trees are very tolerant and resistant to this type of pollution, so we're now planting Ficus trees on all streets.”

The General Management of Environmental Preservation last year conducted research entitled, “Exhaust pollution and its physical and mental effects upon humans,” based on the results of medical testing on human blood samples obtained from numerous Sana'a residents.

The study focused on the percentage of lead in the blood, as that is the most dangerous element of exhaust pollution. The accumulation of this element in the blood makes a person nervous and depressed. The percentage was high in taxi drivers' blood, averaging 5.5 percent, followed by traffic police at 4.7 percent.

The study further noted that Yemen lacks scientific studies clarifying the diseases to which its trees may be exposed due to such pollution.

“Trees of the same species growing in identical locations may vary in their susceptibility to damage. For example, one tree may show no sign of the problem, while the tree next to it will drop brown leaves and die. Older leaves are most likely to show symptoms because they've been exposed to exhaust pollution for longer periods,” the study noted.

Lack of awareness among farmers also may exaggerate the problem. As one Hadda Street farmer, Jihad Al-Yadie, says, “We sometimes see trees decline and become pale, but we don't know the reasons. I see engineers put chemical fertilizer on them.”

Although air pollution does pose many risks, experts believe there are workable and acceptable solutions, however, some require research, application and time.

Sharaf Al-Hamzi, manager of the Environmental Guidance Center in Sana'a, suggests, “We must prevent the importation of diesel engines, as well as find some type of device that can be placed on vehicle exhausts to reduce this type of pollution.”

Ba-Quhaizel, the Environmental Observation and Evaluation General Manager in the General Management of the Environment Preservation, concludes, “Expanding green areas is an important solution. We must use the media and schools to teach people and students about the importance of increasing the planting of trees. Additionally, we must choose those types of trees that tolerate difficult environmental circumstances.”