Smog. I think most people have experienced driving into a city & seeing (& smelling) the change in air quality. Spend too much time breathing it & you'll suffer from a number of respiratory ailments (and who knows what else?). Smog is mainly composed of 6 dangerous substances: sulfur dioxide, carbon monoxide, ozone, nitrogen dioxide, lead and particulate matter. Sulfur dioxide is probably what you smell - a waft of rotten eggs - and makes your nose tingle. It's also the culprit for acid rains. Everyone should have heard of the dangers of carbon monoxide - this gas binds to your hemoglobin (talked about last week) more strongly than oxygen, meaning you essentially suffocate while still breathing. Ozone is protective when it's far up in the stratosphere, but when at ground-level, it's a harmful pollutant. It is produced when nitrogen dioxide reacts with volatile organic compounds. Both of these gases are harmful because they cause the release of free radicals, which cause widespread injury in all cells, including DNA damage that can lead to cancer. Lead poisoning is nothing new - but who knew pollution could slowly be doing it? Particulate matter is basically soot. Small particle that clog up the lungs & cause a lot of inflammation.
Sounds lovely doesn't it? But before you start blaming modern society for all this smog... pollution has actually been around for a long time. In fact, in 1306, King Edward I passed the first environmental control law. It stated: "whoever should be found guilty of burning coal shall suffer the loss of his head." Later on, in 1661, John Evelyn wrote that residents of the city of London suffered from "catharrs, phthisicks & consumptions" - which translates to bronchitis, pneumonia & tuberculosis. This was brought on by the air they breathed: "nothing but an impure and thick mist, accompanied by a fuliginous and filthy vapour, which renders them obnoxious to a thousand inconveniences, corrupting the lungs, and disordering the entire habit of their bodies." Seems that the only things that have changed are the sources of pollution, the regulations controlling it and the medical remedies for the diseases it causes.