6.4 Acid Deposition (Rain)

The pH Scale…What is acidic?

Acidity Rain is naturally slightly acidic pH 5.6 Caused by carbon dioxide in the air dissolving into the water forming carbonic acid

https://www.youtube.com/watch?v=Nf8cuvl62Vc However, when sulfur and nitrogen oxides dissolve in the rain they form sulfuric and nitric acid and can have a very low pH (1-3) pH scale is logarithmic, pH1 is x10 more acidic that pH 2, and x100 stronger than pH 3

Acid Deposition (Process)

Chemistry of acidified precipitations Acid deposition can be either wet or dry: Wet deposition - acidic rain, snow, or other precipitation Dry deposition - acidic gas or dry particles, not mixed with water Pollutants can be classified as either primary or secondary: Primary pollutants - those directly emitted by a factory or automobile SO2 - sulfur dioxide NO and NO2, usually identified as NOx

Primary pollutants by source

Chemistry Cont. Secondary pollutants - primary pollutants react with other substances in the atmosphere and create different pollutants H2SO3 - sulfurous acid H2SO4 - sulfuric acid HNO3 - nitric acid

Effects of acid deposition on environment Direct effects (Know 1): Inhibits embryonic development of fish Chlorophyll loss & yellowing of tree leaves and buds → diminished growth Thinning of cuticle (the waxy coating on needles) Symbiotic root microbes killed (i.e. Rhizobium spp. and other beneficial fungi)

Effects of acid deposition on environment Toxic effects (Know 1): Aluminum (Al) leaches out of soil into streams Al disrupts salt, water, and oxygen regulating mechanisms in fish Al can also adhere to fish gills, causing suffocation Lichens sensitive to SO2 gases and used as indicator species

Effects of acid deposition on environment Nutrient effects (Know 1): Soil particles can’t retain Ca, Mg, K, and other nutrients in acidic environment, so those nutrients are leached out of soil and not available to trees Dissolved Al ions damage root hairs (the smallest roots, which are the most effective at absorbing nutrients), so the trees are unable to absorb as many nutrients N-fixing bacteria don’t function as well, so less N is added to soil matrix

Effects of acid deposition on environment Damage to human infrastructure: acid rain dissolves limestone structures, especially buildings and statues

Acid deposition is regional Acid precipitation falls back to Earth rather than entering stratospheric jet stream Most areas are downwind of pollution sources Canadian forests damaged by coal-fired power plants in USA Scandinavian and German forests damaged by British coal plants

Potential problem areas because of sensitive soils Potential problem areas because of air pollution: emissions leading to acid deposition Current problem areas (including lakes and rivers)

Reducing the effects of acid deposition find out about the following techniques: Liming lakes to neutralise acidity. Precombustion (before burning) techniques. End of pipe measures (after burning). Of course we could always reduce our use of fossil fuels to help solve this problem. Nuclear power? Electric cars?

Pollution management strategies for acid deposition See Table 15.7 on p.298 of the IB ESS 2010 Course Companion Replace Switch to renewable energy sources (reduce fossil fuel use) Increase energy efficiency (better light bulbs and appliances) More public transportation (fewer automobiles on the road) Use low-sulfur fuels Regulate Install ‘scrubbers’ on smokestacks of coal-fired power plants to remove SO2 Catalytic converters installed on automobiles (required by law in the US, Canada, and Europe)

Management cont. Freshwater ecosystems much more vulnerable Restore Add limestone to acidified lakes and streams Using limestone or calcium carbonate (CaCO3) can neutralize (buffer) the impact of acids. Freshwater ecosystems much more vulnerable Expensive and hard to determine how much to add

Remember, this is not a Global problem but a regional one most serious in Mountain top forests Areas with high auto traffic Areas downwind from industrial centers

CASE STUDY Research the effect of acid deposition and intergovernmental agreements or legislation and their effectiveness In groups you are going to create a poster to show the impact and pollution management strategies in one of the cases below. Canada affected by acid deposition from the USA. Sweden and Norway affected by acid deposition from Poland, Germany and UK. China