Atmospheric Oxygen Decline Due to Fossil Fuel Combustion

This is another issue I have wondered about. When something is burned, what is happening is that some substance is combining with oxygen to produce energy. Burning fossil fuels should remove some oxygen from the air.

I don't know that the fact that the air in cities can have significantly less oxygen proves is really a sign that we are not yet being adversely affected. I and others sometimes feel it is hard to breathe at times, and feel much better away from cities, in natural areas, like walking in the woods.

http://www.climateemergencyinstitute.com/atmos_oxy_karen_v-t.html

Karen Villarante-Tonido, Philippines
Original Post: Feb. 14, 2012

There has been much focus on the negative impacts of rising carbon dioxide (CO2) levels in the atmosphere due to fossil fuel combustion in recent years. This is not surprising, considering the large percentage of fossil fuel CO2 that continues to accumulate in the atmosphere since the industrial revolution. Because the concentration of CO2 in the atmosphere is small relative to other gases (only about 0.038%), the excess CO2 generated from burning of fossil fuels creates an impact large enough to affect global temperature, climate, ocean chemistry and consequently, human and animal health, welfare and the environment.

In contrast, it is only recently that some attention has been directed towards the impact of fossil fuel burning on the level of oxygen in the atmosphere. New research shows that atmospheric oxygen levels have been declining while CO2 levels are rising due to fossil fuel combustion. This problem has only been brought to light fairly recently since the technology for taking measurements of minute variations in atmospheric oxygen has only been available in the late 1980s (Klusinske, 2010).

It was Dr. Ralph Keeling who made observations of the level of atmospheric oxygen over a period of about 20 years (See Figure 1 below). From his stations stretching north from Antarctica to areas in and around the Pacific and Atlantic Oceans (specifically, in La Jolla, California and Cape Grim, Tasmania), Dr. Keeling found a 0.0317% decline in atmospheric oxygen from 1990 to 2008 (Klusinske, 2010).

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Dr. Keeling estimated that the about three oxygen (O2) molecules are lost every time a single CO2 molecule is produced by fossil fuel combustion. When CO2 is produced during fossil fuel combustion, O2 from the atmosphere is used up in the process. From the molecular formula of CO2 alone, it seems that only two O2 molecules are lost every time one CO2 molecule is produced. But Dr. Keeling explained that the Oxygen:Carbon combustion ratio of a fossil fuel depends on its hydrogen content. He said it can vary from 1.2 for coal, 1.45 for liquid fuels and 2.0 for natural gas. While considering these factors, Dr. Keeling came up with the 3:1 ratio of oxygen lost per carbon dioxide produced.

The burning of fossil fuels may also potentially cause a decline in atmospheric oxygen levels indirectly by affecting oxygen-producing organisms such as phytoplankton.

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Photosynthesis accounts for 98% of the world’s oxygen output while the splitting of water molecules by ultraviolet (UV) radiation accounts for the remaining 1-2%. Photosynthesis by phytoplankton species is said to produce oxygen that equals half of the world’s oxygen output. The other half is produced by photosynthesis in terrestrial plants.

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Because of the varied effects of ocean acidification and warming on different phytoplankton species, it is also unclear whether the increase in fossil fuel CO2 actually causes a decline in atmospheric oxygen levels.

At this point, it is already known that atmospheric oxygen is declining. What surprised Dr. Ralph Keeling was the finding that the rate of oxygen decline was less than he expected. It was less than what could be accounted for by fossil fuel combustion. With the reality of deforestation, conversion of agricultural land into urban and industrial areas and destruction of natural ecosystems, the rate of oxygen decline is even expected to be greater, but it was not the case. (Johnston, 2007)

There are several theories that might explain this finding, according to Dr. Keeling and Scrips marine chemist, Andrew Dickson. One is that plants could be growing more rapidly (plant biomass increasing) since there is more carbon dioxide and nitrogen available for plant growth. And because farming practices have become more efficient, some areas have become reforested and thus, more plants are available for oxygen production, thereby buffering the effects of oxygen decline. (Johnston, 2007)

But like any other system, the ability of nature to adapt and buffer environmental changes is not limitless. There is a need to mitigate abuses to the environment and prevent the current situation from worsening.

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For instance, the production of biochar will definitely accelerate deforestation, which could further decrease oxygen output. Also, “biochar itself is an oxygen sink in the course of degrading in the soil” (Ho, 2009). In the end, this proposal could be dangerous to humans and animals alike.

At the moment, the percentage of oxygen decline is too small to worry about. The oxygen in the air remains abundant despite the reported decline. Nevertheless, we should not be complacent or laid-back. The current high concentration (20.95%) of oxygen in the atmosphere is what humans and oxygen-breathing animals need to survive. Lack of oxygen can cause serious implications on our health.

Enclosed spaces with an oxygen concentration of 19.5% instead of the current 20.95% is already said to be oxygen-deficient (Ho, 2009). A concentration below 19.5% is no longer healthy and safe for humans and animals. At this concentration, it is difficult for the body to bring oxygen to all its cells and organs, a feat necessary for the system to function efficiently. First and foremost, this places a strain on the heart, which struggles to pump blood fast enough to oxygenate all cells of the body. If blood is not oxygenated enough, then the heart will have to work much harder. Aside from heart disease, cancers and other degenerative diseases can develop at these very low oxygen concentrations and at even lower concentrations of 6% to 7%, life can no longer be sustained. (Tatchell, 2008)

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Although atmospheric O2 levels are gradually declining as CO2 continues to accumulate in the air from fossil fuel combustion, fortunately an O2 crisis is not yet a likely scenario. Oxygen is quite abundant in the atmosphere that even when fossil fuel reserves (mostly coal) are exhausted, the maximum potential loss in oxygen is only small (Broecker, 1970). The oxygen decline of 0.0317% is considered not significant and should not arouse serious concern at this point. Mr. Ray Langenfelds of Commonwealth Scientific and Industrial Research Organisation (CSIRO) Australia further adds that this level of oxygen reduction actually has no impact on our breathing (Science Daily, 1999). He said that typical oxygen fluctuations indoors or in city air can actually be greater than this.

In fact, scientists agree that today, oxygen levels are even less than 20.95% in certain areas such as densely populated, polluted city centers and industrial complexes (Tatchell, 2008). According to a UN adviser, Professor Ervin Laszlo, “Currently the oxygen content of the Earth’s atmosphere dips to 19% over impacted areas, and it is down to 12% to 17% over the major cities” (Tatchell, 2008). Hence, the oxygen decline currently recorded is still not a serious environmental concern at this point.

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But perhaps the most obvious and simple solution to the problem of declining oxygen levels in the atmosphere is to decrease, if not completely stop fossil fuel burning while shifting to non-carbon based sources of energy (Johnston, 2007), stop deforestation and destruction of natural ecosystems and plant trees.