5.8 Acid Deposition (Rain)

The pH Scale…What is acidic?

Acid Deposition (Process)

Chemistry of acidified precipitationsAcid 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 automobileSO2 - sulfur dioxideNO 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 pollutantsH2SO3 - sulfurous acidH2SO4 - sulfuric acidHNO3 - nitric acid

Effects of acid deposition on environment

Direct effects (Know 1):Inhibits embryonic development of fishChlorophyll loss & yellowing of tree leaves and buds →

diminished growthThinning of cuticle (the waxy coating on needles)Symbiotic root microbes killed (i.e. Rhizobium spp. and

other beneficial fungi)Toxic effects (Know 1):

Aluminum (Al) leaches out of soil into streamsAl disrupts salt, water, and oxygen regulating

mechanisms in fishAl can also adhere to fish gills, causing suffocationLichens 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

Acid deposition is regional

Acid precipitation falls back to Earth rather than entering stratospheric jet stream

Most areas are downwind of pollution sourcesCanadian forests

damaged by coal-fired power plants in USA

Scandinavian and German forests damaged by British coal plants

Pollution management strategies for acid deposition

See Table 15.7 on p.298 of the IB ESS 2010 Course Companion

ReplaceSwitch 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

RegulateInstall ‘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.Restore

Add limestone to acidified lakes and streamsUsing 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