Do urban trees remove air pollution and save precious lives?

Melbourne has an entire map dedicated to urban trees Citygreen

Trees are an integral part of our ecosystem giving us shadow, food and vegetables, besides providing shelter for birds and animals. Little do we know that they not only protect our environments against soil degradation and erosion in the hilly areas but also cut down air pollution. Living in a barren land is tantamount to living in the Hades. In the last decade or so in many parts of Asia, particularly in India in the name of urbanization  thousands  of trees are felled down to  make ways for housing development, building of new highways, industries, etc and in the aftermath  the tree covers in many Indian cities have shrunk considerably leading to increasing heat- radiation and air pollution. Consequently people are living among  fewer trees and are more exposed to fine particulate air pollution- less than 2.5 microns. According to the UN World Health Organization (WHO), about 90% of the global population living in cities in 2014 was exposed to particulate matter that exceeded the WHO air quality guidelines. It is a gloomy foreboding.

trees reduce run-off.

If unchecked,  fine particulate air pollution will cause a host of serious heath problems such as pulmonary inflammation, sinusitis, premature mortality, accelerated atherosclerosis, altered cardiac function, etc. A study conducted in ten US cities by the US Forest Service - Devey Inst. has found that there is a direct correlation between total tree cover and its impact on PM2.5 concentration. The more tree cover in a city, the lower the PM2.5 concentration. Particulate matter (PM) is microscopic particles that become trapped in the lungs of people breathing polluted air.  A study by US-based The Nature Conservancy (TNC) reported than the average reduction of particulate matter near a tree was between 7% and 24%. But, unfortunately in most of the surveyed cities, the tree cover is on the decline, which is not good.  So, in the urban and semi urban areas trees form an effective filter against fine particle air pollution and play a vital role by providing cleaner environment.

A study by US-based The Nature Conservancy (TNC) reported than the average reduction of particulate matter near a tree was between 7% and 24%.  According to the study PM pollution could  cause  an estimated 6.2 million lives each year by 2050 and this scary. That urban trees are quite beneficial to the people is scientifically proven. The lead author Dr McDonald points out,  "The average reduction of particulate matter near a tree is between 7-24%, while the cooling effect is up to 2C (3.6F). There are already tens of millions of people getting those kinds of benefits'' Planting trees is a cost-effective way to tackle urban air pollution, which is a growing problem for many cities. Unlike growing trees, other methods of cooling and cleaning air are  positively not cost-effective, whereas  trees are cost competitive.

Congress for the New Urbanism

The WHO Health Statistics 2016 says air pollution is "caused by inefficient energy production, distribution and use, especially in the industrial, transportation and building sectors, and by poor waste management". Transport system driven by petroleum products may further increase the pollution problem. People living near the busy roads with poor tree cover are more exposed and  affected because of poor air quality.

Dr McDonald observed: "We also looked at how much more trees could help if we planted more trees. We found that there was a lot more scope there. All of the cities we looked at, if all the people in them spent an extra US $4 a year on planting trees, you could save between 11,000 and 36,000 lives each year. This is mostly as a result of having cleaner air.

Planting trees in an urban setting has some draw back, one being with respect to  the flow of air in heavily polluted streets with heavy traffic. Thick canopies of tree can limit the circulation of air, trapping the poor quality air at low levels, where people breathe. In a scenario like this air-flow is very important and we need good
planting strategy.  In a very busy street with a high flow of vehicles,  the advice is to ensure there is enough space between  trees to ensure that they  are still getting enough air flow in order to prevent that negative outcome. In the residential area, this air-flow blockage is not a big hurdle. 

In a 2014 report, on the benefits of the  London's trees pointed out "at least £133 million of benefits every year in terms of air pollution removal, carbon sequestration and reducing the amount of water going into drains".

It is imperative that the urban city development authorities across India before venturing into a new project should seriously ponder and actively engage in increasing the tree cover in cities and its suburbs. Since millions of people move into urban and suburban areas, these people are at health risk. Lots of tree cover will help the future generation lead a better, healthier life free from air pollution.
Related Internet links: The Nature Conservancy Trees for Cities World Health Organization