Reported to shorten the lives of thousands of people a year, increased air pollution in our major towns and cities has become a national talking point. After all, the subject isn't simply an environmental issue, but one that could have a serious impact on our general health. With NOx (nitrogen dioxide) being said to "decrease lung function", and therefore increase "the risk of respiratory conditions" for many, our 'dirty air' has the capacity to significantly undermine the health of those people with existing heart or lung conditions.
"...because of industrial growth and urban expansion, we now contribute 300 million tons of pollution per year to the atmosphere, much more than natural systems can safely absorb." US DEPARTMENT OF AGRICULTURE
Source(s) But how does this polluted air come about, and, more importantly, how can we look to decrease NOx particulates in the air that we breathe? According to our government, the source of our dirty air lies in diesel engines and the dangerous particles they emit. This would make sense. After all, the areas of most concern - heavily built-up towns and cities - are also those areas most affected by heavy traffic and daily commuters. Evident in a report that told of how one road in London was said to have broken the annual limits for NOx in just five days - presumably because of the dense traffic operating in the area.
Despite this, diesel engines aren't the only contributors to the production of the deadly gas. Other factors, such as smoking, cooking, and housing development all being linked to heightened levels of nitrogen dioxide - and therefore, to the likelihood of ill-health.
Considering this, the recent government proposal to ban diesel vehicles from future 'pedestrian-only' areas of London, alongside the vision of raising the annual tax for those diesel car holders, seems somewhat dubious. After all, raising the tax on diesel cars won't necessarily deter any buyer from purchasing a vehicle in the first place. Equally, creating purely pedestrianised areas would require a great deal of disruption and urban development - two significant contributors to the production of NOx.
Nevertheless, the status air pollution has gained in parliamentary debate, and the considerations being presented in order to restore our clean air are nothing but positive steps towards a healthier and safer future.
"In this urban century when there are going to be an extra two billion people in cities, smart cities should be thinking about how nature and trees can be part of the solution to keep air healthy."
ROBERT MCDONALD
Alternative Solutions
There are, however, other less disruptive solutions by which we might look to diminish - or, at least quash - our impact on air quality. Most notably, through the increased introduction of street trees and city plants.
Author of a recent US-based report for the TNC (The Nature Conservancy), Robert McDonald commented that the average reduction of polluted air matter near a single tree was anywhere between "7-24%". A low statistic is might seem, but, he later comments, a contribution that could amount to the saving of between "11,000 [to] 36,000 lives each year".
Considering this, not only would the introduction of more street trees greatly improve the quality of life for those existing in areas where there is currently poor air quality. But, in saving thousands of lives per year, it can be assumed that the strain on our public health system would also be significantly reduced. All for the sake of a bit of greenery!
But how are the trees able to affect the quality of our air to such an extent? It is simply in their nature, it seems; they're built to trap and filter airborne particles. For instance, their waxy, hairy leaves trap pollutants on their surface. Some of these particles are absorbed into the plant itself, whilst the remaining pollutants are simply washed into the soil during the consequent rainfall. In a similar manner, the rough bark on a tree traps pollutants that are later washed to the floor - therefore, even though the tree's ability to intercept airborne particles is greater during seasons when its canopy is at its densest, the textured bark still allows for the plant to have some kind of influence on how our air is filtered.
Strategy
Despite their natural ability to positively influence our air quality. It would, however, be necessary to implement a kind of planting-strategy. After all, whilst having the aptitude to absorb pollutants, canopies also slow air currents. In this sense, were a great number of trees to be planted next to a busy roadside, any pedestrians walking in the area would likely find it harder to breathe - the hindrance of natural air flow resulting in a dense, muggy atmosphere. This, in turn, would likely increase the percentage of polluted particulates in the surrounding area - an outcome we would obviously look to avoid.
So...
Trees have always been a part of the urban landscape. But their presence has significantly diminished and been overlooked in the face of development and construction initiatives. Nonetheless, now that we are aware of our increasingly poor air quality, and the effect re-introducing nature back into our 'city-scapes' could have, perhaps there is the potential to reconsider how we colour our urban areas. Most poignantly, making them suitable as smart cities of the future - living alongside nature.