I recently spent some time walking around Washington DC, where I live, with an aethalometer sticking out of my shirt collar. I carried the device, which measures air pollution, around with me like a pet monkey as I walked in a city park, drove on the city’s circular beltway and picked up my kids from school. It was sadly eye-opening because it confirmed what I have long suspected: my city is a polluted place.
The monitor, borrowed from Columbia University’s Lamont-Doherty Earth Observatory in Palisades, New York, measures black carbon, a byproduct of car engines and other fuel- burning processes. Its name comes from the Greek word meaning “to blacken with soot”. And that’s exactly what happened.
The spindly machine measured high readings of 6,000 nanograms per cubic meter while I drove around, even during off-peak hours. More shockingly, I recorded equally high values just outside my daughter’s school, where cars and buses idle, waiting to pick up students. Much of the pollution there is generated by diesel fuel, which has been shown to shorten life spans around the world by causing cardiovascular and pulmonary problems. Worldwide, fine particulate matter, of which black carbon is a component, is blamed for 2.1 million premature deaths annually.
Scientists have long considered the lungs as vulnerable to air pollution. Only recently have they come to realise the role of the nose as a pathway to the brain; the extent of the nose-brain connection was only illuminated in 2003, when researchers in smog-choked Mexico City found brain lesions on stray dogs.
Unfortunately for city dwellers, the closer we live to these roads, the higher our risk of autism, stroke and cognitive decline in ageing, although the exact reasons haven’t been teased out. Scientists suspect it has something to do with fine particles causing tissue inflammation and altering gene expression in the brain’s immune cells.
“I hold my breath when I’m behind a diesel bus,” Michelle Block, a neurobiologist who studies pollution’s effects on microglial cells at Virginia Commonwealth University, told me.
Regardless of whether people know about pollution, its effects are being felt in other ways too. In one 2008 survey of 400 Londoners by economists George MacKerron and Susana Mourato at the London School of Economics, “life satisfaction” fell significantly – half a point on an 11-point scale – for each additional 10 micrograms per cubic metre of nitrogen dioxide pollution, also a common byproduct of diesel engines.
Because I am strangely driven to probe the unhealthy aspects of my life, I also walked around my city wearing a portable electroencephalogram (EEG) device on my head. I wanted to know how easily I could attain “alpha” brain waves(indicating a calm, focused state of mind) by walking in various parts of the city, including a park.
Research has shown that people who live in cities may suffer more psychological stress than people who live in rural areas. For a study published in Nature in 2011, Jens Pruessner and colleagues at the Central Institute of Mental Health in Mannheim found a 21% increase in anxiety disorders, a 39% increase in mood disorders and a doubled risk of schizophrenia in city dwellers. Urban living was linked to increased activity in the brain’s amygdala – the fear centre – and in the perigenual anterior cingulate cortex, a key region for regulating fear and stress.
Meanwhile, a 2011 study from Portugal found that people living near industrial “grey areas” reported less optimism. This may sound trivial, but optimism is associated with healthier behaviours (such as a willingness to exercise), lower levels of fat in the blood and mental resilience, or the ability to recover from stress.
I uploaded the data from my EEG to a California-based website that read it, fed it into an algorithm, and sent me back this dejected message about my lack of alphas: “This indicates that in this state you were actively processing information and, perhaps, that you should relax more often!”
Both my local park and my house sit under the flightpath of a busy airport, and noise pollution is yet another well-proven source of stress. I decided to measure the noise. This I did in my very own backyard, using an iPhone app. I found out that the jets flying overhead every two minutes cranked out average decibel levels between 55 and 60 but sometimes spiking much higher (60 decibels is high enough to drown out normal speech). These are the same levels linked to stress-related disease and increased use of anti-anxiety medication in European studies. I bought noise-cancelling headphones. And I thought seriously about moving to the Rocky Mountains.
But before we all ditch our cities to camp out in a hay bale, it’s worth remembering that there are some excellent ways to counter the ill effects of crowded, Euclidean, monochromatic, loud modern life. Because, let’s face it, there are still some rather nice things about living in cities. And the fact is, more and more of us live in them. Globally, as of 2008, more people live in cities than outside them. By 2050, another two billion people will pile in, leading one US anthropologist, Jason Vargo, to suggest a new name for our species: Metro sapiens. Learning to make cities livable will be one of the greatest public health challenges of this century.
One clear step is the need to tackle air pollution. Health experts in the UK recently suggested parents cover their babies’ prams during morning rush hour. A better solution would be to regulate the polluters. Paris, Madrid, Athens and Mexico City plan to ban diesel vehicles from city centres within the next 10 years.
Another antidote to noise, particulates and greyness is both delightful and affordable: trees. For humans, urban trees provide not just aesthetic pleasure but health benefits. Trees soak up air pollution, create cooling and provide a brain-tingling array of colours, textures and scents. The birds they shelter provide us with birdsong, which in turn is linked to feelings of wellbeing.
Consider the example of Toronto, Canada. The city values its 10m trees at C$7bn(£4.3bn). A 2015 study there showed the higher a neighbourhood’s tree density, the lower the incidence of heart and metabolic disease, and estimated that the health boost to those living on blocks with 11 more trees than average was equivalent to a C$20,000 gain in median income.
I hope to become so lucky, since Washington DC and partner nonprofits have been trying to plant at least 8,600 trees per year in an effort to increase the street canopy to 40% in the next two decades. New York City recently completed a campaign to plant a million trees, and Los Angeles, Shanghai, Denver and Dubai are in the middle of similar projects.
I envision soon nestling under a sprawling oak and removing all of my monitoring devices. It will just be me and the tree, and I won’t need a machine to tell me I feel better.
- Florence Williams’ The Nature Fix: Why nature makes us happier, healthier and more creative will be published by WW Norton UK at the end of March