Smog, the cloud’s ugly, earthborn sister, is formed when pollutants combine with sunlight, creating what are called particulate matter and Ground-level Ozone. It afflicts many of the world’s major metropolitan areas, and its effects range from irritating to deadly. In London’s Great Fog of 1952, for example, as many of 12,000 people—yes, 12,000—might have died when thick smog engulfed the city for nearly a full week!
We emit a ton (or more accurately, tons) of pollutants everyday: factories, cars, and coal-burning power plants all emit Nitrogen Oxides (NOx); liquid solvents and fuels evaporate and release Volatile Organic Compounds (VOCs). Sunlight triggers a reaction in these highly reactive chemicals, leaving particulate matter and Ground-level Ozone. This is called photochemical smog, and is the type of smog that anyone who has ever spent time in a large city knows all too well.
Urban Smog
Cities with warm, dry climates usually have the worst smog. This is because stagnant air traps pollutants, and the sun’s intense heat causes them to react chemically. A city’s geography also contributes to the presence of smog. Cities in valleys or basins tend to trap smog that in a flatter area would be blown away with the wind. This is one reason why Los Angeles holds the title of the United State’s smoggiest city, and also why Mexico City is considered the world’s smoggiest city—both are in mountain basins, which essentially keep the smog from going anywhere.
A bigger contributing factor to the hazy skylines of LA and Mexico City is the number of drivers on their roads. LA’s underutilized public transportation system and decentralized layout mean that over 12 million1 frustrated drivers start and stop along the 405 or a nearby highway everyday. Mexico City has 18 million people and 33% of them said they use a car as a regular means of transport in 2007.2 In contrast, only 74,000 people reported using the metrobus daily.3 The emissions from Mexico City’s driving fleet are exacerbated by the fact that their cars are an average of 10 years old. They also often use low-grade fuel, with their cars struggling to run efficiently at the city’s 7,000 foot altitude.4
For most people in LA, Mexico City, and the dozens of other cities worldwide considered to have seriously unhealthy air, smog is only a mild irritant of the eyes, nose, and throat.5 However, smog’s effects extend far beyond this, especially for anyone with a pre-existing condition. Those with a history of heart and lung problems—emphysema, bronchitis, asthma—are at risk for having their conditions worsened by smog. Lung cancer and even brain, kidney, and liver damage could result from long term exposure.6 Adult onset asthma is also on the rise worldwide, an increase which correlates with the growth of smoggy megalopolises.
The Great London Smog
Long smoggy, London was at one point the world’s most polluted city, and has been associated with peasoup mists for centuries. An indication of just how bad it used to be:
“Beijing’s poor air quality – 300 or so micrograms of particulate matter per cubic meter – has [received plenty of criticism], but London’s numbers in the 1950s were consistently above 400.”
In 1952, things went from bad to worse in London when its levels “surged to 1,600 during [what is now called] the Great Smog.”7 The Great Smog sounds like the premise for some sort of 1950’s horror movie: snaking tendrils of fog invade a city, bring all activity to a standstill, and take thousands of lives. But this actually happened, the product of a perfect storm of circumstances.
The Great Smog resulted from two factors: unusually cold temperatures and a subsequent increase in coal-burning by Londoners trying to keep warm. During cold weather, a process called temperature inversion can occur. Temperature inversion is not at all uncommon, especially during a London winter. Usually, air closer to the ground is warmer than the air above it, and so rises. However, during cold winter nights, the ground sometimes cools to such an extent that it also cools the air around it. This causes a “mist to form as water vapor precipitates on dust particles.”8 In other words, temperature aversion creates a fog that usually burns off when the sun rises the next morning.9
The fog didn’t burn off on the morning of December 5th, 1952, however. The weather had been cold even for Londoners, and the resultant increase in their coal burning combined with the city’s usual factory emissions (remember, London is the birthplace of the Industrial Revolution) to create a layer of smog too thick for the sun to break through. It wasn’t until almost a week after forming that the Great Smog was blown westward along the Thames River. Until that windy day on December 10th, Londoners were living in the midst of “tons of black soot, sticky particles of tar, and gaseous sulfur dioxide.”10 People in some areas of the city were unable to see a foot in front of them. There were reports of theaters closing when they were invaded by the smog. Transportation services were crippled. The entire city basically stopped moving.
However, the highest cost to London was not that of productivity but of life. Calculating the death rate is a tricky matter, and while official estimates place the death rate during and following the fog at 4,000 people, another study places it closer to 12,000 people. Most of those who died had pre-existing conditions and/or were elderly. The main causes of death were: pneumonia, bronchitis, tuberculosis, and heart failure.11
After the Great Smog, England’s Parliament passed two clean air acts. In between that legislation and today, London has gone from being an environmental offender to having some of the cleanest air of any major city. The historical curiosity that is the Great Smog should not terrify us. What it should do is remind us of the many ways in which even our simplest actions can affect the earth’s feedback cycles, and maybe encourage us to finally buy that bike.
