Sunday, March 18, 2012

Air quality


As more people become eco-minded, the topic of breathable air quality becomes an increasingly important issue. More and more people are attributing air freshness and cleanliness to more than just levels of humidity; but also to the health implications the molecular components in air have on human health and life longevity. The transportation sector is undoubtedly a major determinant in the quality of air that we live and breathe in.
Recently I conducted an air quality experiment in my Instrumental Analysis lab at Portland State University. We were interested in the concentration of toluene (a hydrocarbon present in gasoline) in air. We collected air from three different sites around downtown Portland. The results are tabulated in Table 1:
Table 1: Concentration of xylene and toluene in parts per billion by volume
Sample Site

[Xyl] in Bag (ppbv)
[Tol] in Bag (ppbv)
SW FB Field

34.8
29.6
Mont/Park N

24.9
153.2
10th/Market SE

33.6
58.4

From table 1, the concentration of toluene in the football field was lowest, the intersection of 10th and Market St. was the second lowest, and the intersection of Montgomery and Park was the highest. Since this experiment presumes that gasoline from automobiles is the primary source of toluene in air, the good news is that there is no real correlation between high traffic area and higher toluene concentration, possibly because the toluene concentration in air in downtown Portland is low, but it doesn’t mean that there aren’t other major sources of toluene pollution
Also interesting is that greenhouse gas CO2 was found to be linked to the toluene vapor that gets released into the air. For every toluene molecule that gets released seven potential CO2 molecules are created via reaction with oxygen. There were between 1.65 x 1023 molecules C and 2.30 x 1023 molecules C that is released into the air via toluene vapors.  In volume fractions these numbers correlate to a range of 2.07 x 102 ppb to 1.07 x 103 ppb of carbon in air, which is an insignificant number compared to the 0.039 % C that makes up the Earth’s atmosphere.
We have some good news. Based the amount of toluene in air determined in this experiment, toluene pollution in air is not a cause for concern. The Department of Environmental Services (DES) toluene data sheet states that the toluene odor threshold in air is 8 ppm.1 The threshold for short-term effects (includes drowsiness, headache, nausea, visual changes, muscle spasm, dizziness, and loss of coordination) is 50 ppm. The threshold for chronic, long term effects have not been documented although the fact sheet states that extreme exposure to toluene can lead to nervous system reduction in thinking, memory, muscular ability, hearing and color vision loss, permanent brain toxicity, increased liver and kidney weights. As a reference, the Occupational Safety and Health Hazard set the permissible exposure limit for workplace air at 200ppm over eight hours, and the American Conference of Governmental Industrial Hygienists (ACGIH) set the recommended limit for toluene in workplace air at 50ppm. The amount of toluene in the air samples obtained in this experiment shows to levels of toluene to be below 153 ppb, well below DES, OSHA, and ACGIH standards.
As we can see, there is some good news under all the abysmal planet deterioration talk. However, the data does indeed confirm that gasoline is a major source of potentially harmful substances like toluene and carbon dioxide. A potential danger I see from this is that certain harmful effects can be subtle and build up over a long period of time, such that it cannot be immediately linked to gasoline vapors. The more I study about petroleum and petroleum based products, the more I feel the need to raise awareness and lessen our consumption of petroleum.
REFERENCES:
1.     New Hampshire Department of Environmental Services. http://des.nh.gov/organization/commissioner/pip/factsheets/ard/documents/ard-ehp-4.pdf. Environmental Fact Sheet: Toluene health Information Summary. March 11, 2012.

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