Acid Rain Flashcards
Acid rain
It is formed when oxides of Sulphur and nitrogen react with moisture in the atmosphere
Rain with pH of less than 5.6
Acid rain damages lakes, streams, forests, plants and animals that live in these ecosystems
Types of acid deposition:
1) Acid rain (mixture of wet and dry deposition from atmosphere)
2) Wet deposition (if acid chemicals in the air are blown into areas where the weather is wet, acids can fall to the ground in the form of rain, snow, fog or mist).
As acidic water flows over and through ground, it affects variety of plants and animals
Strength of effects depends on several factors like how acidic the water is, the chemistry and buffering capacity of soil involved, types of fish trees and other living things that rely on the water etc.
Precipitation removes the gas particles from atmosphere by two processes: rain out, is corporation of particles into cloud drops that fall on the ground and wash out occurs when materials below cloud is swept down by rain or snow.
3) dry deposition: in areas of dry weather, acid chemicals are incorporated into dust or smoke and fall to the ground through dry deposition, taking to ground, building, vegetation, cars, etc.
Dry deposited gases and particles can be wash from the surfaces by rain stones through run off. The runoff water mix mixture more acidic.
About half of acidity in the atmosphere falls back to earth through dry deposition.
pH scale:
pH scale is measure of how acidic or basic (alkaline) solution
Ranges from 0 to 14 (pH of 7 is neutral)
Devised in 1909 and it is logarithmic index for hydrogen ion concentration in aqueous solution
pH values decrease as hydrogen ion levels increases
Solution with pH 4 is 10x more acidic than solution with pH 5, and 100x more acidic than a solution with pH 6.
While the pH range is usually 0-14, lower and higher values are theoretically possible.
Sources of compounds causing acid rain
Sulphur: natural sources: seas and oceans, volcanic eruptions, biological processes in soil like decomposition of organic matter.
Man-made sources: burning of coal (60% of SO2), petroleum products (30% of SO2), smelting of metal sulphide ores to obtain pure metals, industrial production of sulphuric acid in metallurgical, chemical and fertilizer industries
Nitrogen: natural sources: lightning, volcanic eruption and biological activity. Anthropogenic sources: forest fire and combustion of oil, coal and gas
Formic acid: biomass burning due to forest fires causes emission of formic acid (HCOOH) and formaldehyde (HCHO) into atmosphere and large fraction formaldehyde gets photo oxidation and forms formic acid in atmosphere
Other acids: chlorine, phosphoric acid, hydrochloric acid (smokestacks), carbon monoxide and carbon dioxide (automobiles) became carbonic acid.
Characteristics of acid rain
Concentrated in industrialized belt of northern hemisphere
Upland and/or mountainous areas, are well-watered by rain and snow
Due to abundance of water, they possess numerous lakes and streams and have more land covered with vegetation
Being upland, they have thin soils and glaciated bedrock
In India, first report of acid rain came from Bombay in 1974, instances of acid rain are being reported from metropolitan cities.
Chemistry of acid rain
Atmosphere receives oxides of Sulphur and nitrogen from natural and man-made sources
Some oxides fall back directly to ground as dry deposition, either close to place of origin or some distance away
Sunlight formation of photo-oxidants (ozone) in atmosphere
Photo-oxidants interact with oxides of Sulphur and nitrogen to produce H2SO4 and HNO3 by oxidation
Oxides are of sulphur and nitrogen, photo-oxidants, and other gases (like NH3)
Containing ions of sulphate, nitrate, ammonium and hydrogen falls as wet deposition
Impact of acid rain
On soil:
Exchange between hydrogen ions and nutrient cations like potassium and magnesium in soil cause leaching of nutrients, which makes the soil infertile
Accompanied by decrease in respiration of soil organisms
Increase in ammonia in soil due to decrease in other nutrients decreases rate of decomposition
Nitrate level of soil found to decrease
Impact of acid on soil is less in India because Indian soils are alkaline with good buffering ability
On Vegetation:
Acid rain affects trees and undergrowth in forest in several ways, causing reduced growth or abnormal growth.
Typical growth decreasing symptoms are: discoloration and loss of foliar biomass, loss of feeder root biomass in conifers, premature senescence (aging) of older needles in conifers, increase in susceptibility of damaged to root and foliar pathogens, death of herbaceous vegetation beneath affected trees, prodigious production of lichens on affected trees, death of affected trees.
On microorganisms:
The pH determines proliferation of any microbial species in particular environment and rate at which it produces
Optimum pH of most bacteria and protozoa is near neutrality, most fungi prefer acidic environment, most blue green bacteria prefer alkaline environment
After long run of acid rain, microbial species in soil and water shift from bacteria bound to fungi bound and cause an imbalance in micro flora
Cause delay in decomposition of soil organic material and increase in fungal disease in aquatic life and forests
On Wildlife:
Effects of acid rain on wildlife is not obvious and difficult to document
Director indirect effects of acid rain on productivity and survival of wildlife populations have been reported
Acid rain directly affects eggs and that was a frogs and salamanders that breed in small forest ponds
As postulated, acid rain indirectly affects wildlife by allowing metals bound on soil and sediments to be released into aquatic environment by animals like birds that feed in such an environment
Indirect effects of wildlife are loss or alteration of food and habitat resources
On humans:
Bad smells, reduced visibility, irritation of skin, eye and respiratory tract
Direct effects include chronic bronchitis, pulmonary emphysema and cancer
Some indirect effects are food poisoning via drinking water and food
Increase in levels of toxic heavy-metals like manganese, copper, cadmium and Aluminium contribute to detrimental effects on mental health.
On socio-economics conditions:
Adverse impact on farming and fishing leads to the deterioration in life quality indices like the GNP and per capita income in agricultural and developing countries like India.
Trigger effect of acid rain on pollutants:
Low pH of rainwater and subsequent increased acidity in environment can trigger of or aggravate effects of certain harmful pollutants
1) Mercury:
Methyl Mercury and related short chain alkyl mercurial compounds are most dangerous to human beings accumulate in edible fish tissue
Acid deposition does not increase production of methyl Mercury but it increases the partitioning of methyl Mercury into water column
Use of lime has held in reducing Mercury levels in fish
2) aluminium:
Acidified waters are known to leach substantial amount of aluminium from watersheds
Even at relatively low levels, aluminium has implicated been in dialysis, dementia, disorder of the central nervous system, maybe toxic to individuals with impaired kidney function.
3) Cadmium:
Cadmium can enter drinking water supply through the corrosion of galvanized pipe or from copper zinc through corrosion of galvanized Piper or from copper zinc solder used in the distribution systems
4) Lead:
Foetuses and infants our highly susceptible to drinking water lead contamination
High blood levels in children (<30 mug/ml) are believe to induce biochemical and neurophysiological dysfunction
5) Asbestos:
Natural Rock released by acidic waters
Control measures
Reducing or eliminating sources of pollution
Buffering (practice of adding neutralizing agent to acidified water to increase pH)
Reducing emission of SO2 from power stations by burning less fossil fuel, using alternate energy sources tidal, wind, hydropower, etc.
Using low sulphur fuel.
Desulphurisation
Decreasing emission of NOx from power stations
Modification of engines
Emissions of SOx controlled by
Converting to sulphuric acid
Converting to elemental sulphur
Neutralizing it and using it in manufacture of other products
