Re: Does air affect the pH of soil?

You ask a very interesting question. I’ll start off with a few definitions. Air is made up mostly of nitrogen (76%) and oxygen (23%), the remaining 1% is a mixture of many trace gasses including carbon dioxide, argon, helium, and water vapor. pH (or the negative log of the hydrogen ion concentration) is a scale which measures acidity (pH<7) or bacisity (pH>7). The pH of soil varies depending on the make-up (sand, humus, clay, etc.). Most soils in the US are slightly acidic having a pH around 6.5. The pH of soil is very important for the proper growth of plants. Check out http://charlottesgardens.com/ ph.html for a brief discussion on pH and plants. In general, air has little effect on the pH of soil. Both nitrogen and oxygen are neutral molecules and do not change the soil pH. Carbon dioxide, although a minor component of air, is slightly acidic when dissolved in water. The carbon dioxide present in our atmosphere dissolves in the water to produce a weak acid known as carbonic acid. Pure rainwater does not effect soil pH to any great extent. In some parts of the US, especially where coal, oil and gas are burned for energy and in areas with high automobile use, air contains high levels of atmospheric pollutants. These pollutants are mostly sulfur dioxide (S02) and oxides of nitrogen such as nitric oxide (NO) and nitrous dioxide (N02). They combine with water in the atmosphere to produce sulfuric acid and nitric acid, respectively. These acids produce a much lower pH than carbonic acid and can lower soil pH to a level when plants will not grow well. Check out the following website to learn more about pH, rain and acid rain; http:// www.necc.mass.edu/MRVIS/MR1_6/start.htm