ess: chapter 6 - atmospheric systems and society

atmospheric structure

1. tropo

2. strato

3. meso

4. thermo

5. exo

atmospheric composition

78% nitrogen

21% oxygen

1% CO2, argon, water vapour, ozone, etc

enhanced greenhouse effect

dangerous version; GHG in atmosphere reducing heat loss instead trap heat energy from surface and reradiate it

troposphere

to 10km

stratosphere

10-50km

ozone

• good in stratosphere, bad in troposphere

• is sometimes a GHG, not always

ozone layer

1-10ppm thick, in dynamic equilibrium since it is continuously made from oxygen and converted back, UV radiation is absorbed in both

UV radiation

• UV-A, UV-B and UV-C

• less → more energy and harmful

damaging effects of UV radiation

• genetic mutation

• damage to living tissues

• skin cancer

• damage to phytoplankton and zooplankton

beneficial effects of UV radiation

• stimulates production of vitamin D

• treats psoriasis and vitiligo

• industrial use: laser, forensic analysis

positive feedback

something “speeding” the loop

ozone depleting substances (ODS)

CFC/freons:

• propellant in spray can, refrigerant. releases chlorine atoms

HCFCs:

• replacement for CFCs. releases chlorine atoms but with shorter lifetime

Halons:

• fire extinguisher. releases bromine atoms

Montreal Protocol

treaty under UNEP, about reduction of ODS before 2000. best example of international cooperation on environmental issue, precautionary principle in science based decision making. first to recognise that different countries phase out at different times, first with regulations carefully monitored

impacts of urban air pollution

• 1 million premature deaths/year

• 2-5% of GDP lost

• 90% of pollution in LEDCs comes from old motor vehicles

primary pollutants

• emitted directly from process

• natural or anthropogenic

• majorly from combustion of fossil fuels

  • carbon monoxide (incomplete combustion)

  • nitrogen oxides

  • CO2

  • unburned hydrocarbons

  • particulates/PM

  • sulphur dioxide

secondary pollutants

• prim. poll. undergo reactions with chemicals already in atmosphere

• sometimes photochemical reactions with sunlight

• examples

  • tropospheric ozone

  • PAN (peroxyacetyl nitrate)

  • particulates (from gaseous prim. poll.)

formation of tropospheric ozone

nitric oxide + oxygen → nitrogen dioxide → either:

• nitric oxide

• o + o2 → ozone (o3)

effects of tropospheric ozone

• enhanced oxidation

• damage to plants (reduces clorphyll)

• damage to humans

• damage to materials and products

formation of particulates

• burning of organic materials, fossil fuels, especially from poorly maintained diesel engines

• PM10 (smaller than 10 microm) has dangers

  • respiratory filters can’t filter them → asthma, lung cancer

  • many are cancer-causing

  • crops covered, reducing productivity

formation of photochemical smog

• caused by warm, sunny, traffic in combination with fossil fuels or forest fires

• mainly nitrogen dioxide and ozone that has interacted with sunlight

• creates chemicals that oxidise → build up of ozone near ground level

• often formed over large, low-lying cities (in valleys)

• enhanced effect by thermal inversion - warm air on top traps the smog

pollution management strategies against atmospheric pollution

eg.

• consume less

• government regulation

• catalytic coverters

• afforestation

wet deposition

acidic rain/snow

dry deposition

acidic ash or dry particles

acids

• chemicals able to give away hydrogen ion (H+)

• measured with logarithmic pH scale (acidic < 7 < alkaline)

• normal rain is pH 5.6

pollutants causing acid deposition

sulphur dioxide (SO2) and nitrogen oxides (NOx) which react with water to form strong acids (sulphuric and nitric acids)

sources of acid deposition

• SO₂ naturally from volcanic eruptions

• NO₃ from lightning

• fossil fuel combustion in cars

• industry and thermal power stations

formation of acid rain

reactions with oxygen → sulphuric trioxide (SO₃) → sulphuric acid (H₂SO₃) and nitric acid (HNO₃) → very soluble in water, thus acid rain

effects of acid deposition

• direct: weakening tree growth, decreased pH in lakes

• indirect: toxic (increased solubility of metal ions), nutrients (leaching of nutrients)

effects of acid deposition on coniferous forests

1. loss of chlorophyll and damage

2. reduces growth, nutrients washed away, insects entry

3. symbiotic root microbes are killed → decrease in nutrients → decreased growth

4. decreased availability of soil particles to hold nutrients

5. releases toxic aluminium from soil → damage to root hairs

toxic effects of acid deposition

• aluminium ions

• lichens

• nutrient removal (decreased soil fertility)

• buildings

• peat bogs

• human health

pollution management strategies for acid deposition

replace fossil fuels, reduce demand, clean-up at point of emission, catalytic converters, liming forests, international agreements