December 5th marks the 60th anniversary of what is referred to as the "Great Smog" in London. A cold November had more Londoners burning low-quality coal, which had more sulphur dioxide in the smoke, for heat. New diesel buses and gasoline-fueled vehicles on the roads also added air pollution to the atmosphere.
A day before the smog event began, high pressure settled over southern England. High pressure usually keeps air trapped at lower levels of the atmosphere and winds light. This was the case in London as a temperature inversion formed, with warm air trapping the cooler, polluted air at the surface. Fog formed and combined with the pollution to form a thick layer of smog.
Public transport on the surface ground to a halt because they couldn't see the road. Furthermore, ambulances stopped responding to calls, meaning the sick had to get themselves to the hospital. When the rain arrived a few days later, the soot was washed away.
In the months following the event, the deaths of nearly 4,000 people and many more animals were contributed to the event. A study released in 2004 suggests the number of fatalities were as much as triple the estimates made after the event.
Sulphur dioxide, one of the chemicals attributed to the deaths, is a common catalyst in acid rain. However, the compound does have a positive use in winemaking as an antibiotic and antioxidant. You can determine which wine contains the compound by looking for the words "contains sulfites" on the labels.
In the United States, a smog event here in Pennsylvania helped move the U.S. toward clean air legislation. I'm talking about what the New York Times in 2008 called "one of the worst air pollution disasters in the nation's history," Donora in the Monongahela Valley.
In late October 1948, an inversion similar to what London would experience formed over Donora. Within a day, many residents were experiencing signs of respiratory distress. Most of the pollution was being generated by a pair of manufacturing plants in the community. The fire chief and his assistant used the oxygen they had (and nearby communities) to help those in need and using none for themselves.
The smog remained until the 31st when rain returned and helped clean out the atmosphere. By that time 20 residents and around 800 animals had died and between a third and a half of the towns 14,000 residents had been sickened. Lawsuits were filed against the operator of the plants, and were settled for less than what was sought. The plants were closed approximately 20 years later.
If you head to Donora, go to the Donora Smog Museum at 595 McKean Avenue.
The United Nations Statistics Division has an estimate of carbon dioxide (CO2) emissions by country from 1990 to 2009, and you can view the entire table on their website. Carbon dioxide is like sulphur dioxide in that both are air pollutants and formed from combustion. It's a little different though as people emit carbon dioxide when we exhale. Surprisingly, the United States is not the top emitter of carbon dioxide; China is. Combined the countries emit about HALF the total carbon dioxide into the atmosphere each year.
Smog remains an issue around the world, particularly in cities with large populations and commonly under the influence of high pressure. Los Angeles, Houston, and Cario are three examples. Even cities that experience their share of rain or snow (London, New York) deal with smog when high pressure is in place. In 2012, London again violated European Union Air Quality Laws by having daily pollution levels above the legal limit more than 35 days in the year. (This was surpassed with the 36th illegally polluted day in April.)