It seems like it's getting harder and harder these days to find any source untouched by man-made pollution. Especially in the cities, carbon dioxide and organic compounds are pumped out in high quantities by cars, power plants, and other sources. This can produce smog, which in turn can result in all kinds of health problems.
It's important to be aware of this for many reasons, one of which is that smog can be measured. That's right, cities like Los Angeles and Houston (the world's most polluted city) actually measure the level of smog in their air in radio stations throughout the city.
How is this done? What's in the air? Well, in the Los Angeles Basin, it's mostly carbon dioxide, carbon monoxide, ozone (O 3 ), nitrogen dioxide (NO 2 ), and particulate matter (defined below). The levels of all of these vary by time of day and year, with carbon dioxide being the major gas over the entire LA area. In the winter it is replaced by the major pollutant of ozone, while in the summer it is replaced by carbon monoxide.
Nitrogen dioxide is more of a rural pollutant, being more of a byproduct of coal burning and vehicle emissions. Contrary to what most people would expect, the levels of these pollutants, especially carbon dioxide, don't vary a ton throughout the day. That is, it usually doesn't go from being "good" to "bad" in a few seconds.
The main change in the air over the day is due to temperature effects, not pollution effects. In the winter, carbon dioxide is present in much greater quantities in the evening and night, while in the summer it is more abundant in the day. Because of the temperature effect, measuring the air pollution level has been found to be an excellent way to estimate the temperature of the air.
Contrary to what most people would expect, the levels of these pollutants, especially carbon dioxide, don't vary a ton throughout the day. That is, it usually doesn't go from being "good" to "bad" in a few seconds. The main change in the air over the day is due to temperature effects, not pollution effects. Before we get started on the technique, we need to define a few terms:
- Total arbitrary toxic particulate matter (TOTPM): this measurement defines particulate matter in terms of the total amount of particulate matter in the air.
- Particles per million: this measurement defines particulate matter in terms of the concentration of particulate matter in the air. Basically, the two measurements differ in the response, the toxic particulate matter includes all particulate matter in the air and is basically just a number that gets bigger and bigger if more pollution is in the air, while the particulate matter per million is the actual level of particulate matter in the air.