The Acidic Environment > 2. Acidic Oxides >
Assess the evidence which indicates increases in atmospheric concentration of oxides of sulfur and nitrogen
- There is extensive evidence for a considerable increase in the atmospheric concentration of carbon dioxide over the last two centuries.
- The current atmospheric concentration of carbon dioxide is approximately 360 ppm, and this figure is rising.
- Finding evidence for an increase in the concentration of sulfur dioxide and oxides of nitrogen is much more difficult:
- Atmospheric concentrations of these gases are much smaller than that of carbon dioxide (on average, approximately 0.001 ppm).
- The instrumentation required to measure such concentrations has only been available since the 1970s.
- Most sulfates and all nitrates are water-soluble while all carbonates are insoluble, meaning that carbonates stay in inert forms such as in coral, which allows for past concentration levels to be observed, while nitrates and sulfates are chemically changed and thus cannot be used for this purpose.
- The amount of release of these acidic oxides has been far greater since the industrial revolution due to increased burning of fossil fuels.
- Large amounts of sulfur dioxide and nitrogen dioxide are washed out of the air by rain, and therefore there has not been a significant build-up of these gases over time.
- Atmospheric concentrations of these acidic oxides are a greater problem in areas such as Europe and North America than Australia.
- The annual average concentrations of sulfur dioxide and nitrogen dioxide in most large cities are about 0.01 ppm, which is not harmful.
- What is of concern to human health is the number of days per year when the concentrations of these gases exceeds amounts that are considered safe.
Emissions containing sulfur dioxide