Air pollution – Local and Global Concerns

Many atmospheric pollutants are naturally occurring compounds. What are the key human activities that cause levels of these compounds to become problematic?

What is a biogeochemical cycle?

Give an example of a local or regional-scale biogeochemical budget.

Why do we care about global budgets?

What is a flux? A sink? A transformation process?

Discuss the cycling of:

sulfurnitrogencarbon

What sorts of atmospheric and other concerns are caused by each of these in their‘polluting’ form?

Briefly describe the origin and problems associated with

leadozone CFC’s

Hydrogen, oxygen, carbon, nitrogen, and sulfur combine toform a set of ‘environmental gases’ which are cycled throughthe atmo-, hydro-, litho- and ecospheres.

Global Biogeochemical Cycles

What are global biogeochemical cycles?

Global cycles vs. local budgets?

Chemical species involved.

Fluxes, reservoirs and long-term storage

Transport and transformation processes

Examples - Carbon, nitrogen, sulfur

Local or regional ‘budgets’

Balance inputs/output or gains/losses on a localor regional scale.

Example: Solute budget for the Chenango River drainage system.

Inputs/gains: Dissolved salts from precipitation plus dissolved salts from weathering and soils

Outputs/losses: Outflow to streams plus storage in biomass plus outflow as groundwater plus inorganic precipitation in soils

A BUDGET MUST BALANCE ON SOME TIME SCALE

FluxMovement of mass of material from one reservoir to another (measured in mass/time) - often involves atransformation process.

Reservoir (or sink)Place of storage of material. Duration of storage measuredin mean residence time. Storage can be very short (e.g. waterin the atmosphere 2-3 days) or very long (carbon in the earth’s crust - millions of years)

Transport mechanismsAdvection (transport of dissolved ions in water)

Transformation processesPhotosynthesis (carbon fixation), respiration (oxidation ofcarbon), nitrification, denitirification

Forms of Sulfur:

Sulfur oxide gases (SOx) - Combustion of S-bearing fossil fuelsacid rain gas

Reduced sulfur as H2S - Decay of organics; sulfate reduction(oxidizes rapidly to SOx in atmosphere)

DMS -dimethyl sulfide - Organic decay(moderately long-lived gas in atmosphere - oxidizes toSOx)

Sulfate ion in seawater

Pyrite (FeS2) in sedimentary rocks

Sulfur in the Atmosphere:

Sulfate particles in the upper atmosphere increase the reflection of sunlight, especially the visible-red portion ofthe spectrum. Volcanic sulfate ejected into the atmosphere during major eruptions could cause significant global cooling.Ash particles from volcanoes have similar effects.

Significant sulfate loading in the atmosphere results in acid rain. Both volcanic sulfate and fossil fuel sulfate increaseacidity of precipitation.

Many economically important metals - zinc, lead, copper - are found as sulfides. Mining of these introduces locallysignificant amounts of sulfideand sulfate into surface andground waters. The low pH(high acidity) of mine drainagemay mobilize other toxic metalslike cadmium or mercury thatordinarily are quite inert. Theamount of sulfur introduced intothe global budget from miningactivities is insignificant comparedto fossil fuel combustion.

A large number of simultaneous major eruptions could introduceenough sulfur into the atmosphere to cause global cooling.

Use of nitrogenfertilizer is aglobal phenomenon.

Production anduse of nitrogenfertilizers hasfostered the‘Green Revolution’

Forms of Nitrogen:

Most common is N2 (78% of atmosphere) - slightly soluble inwater.

Ammonia - NH3 - soluble in water - oxidizes rapidly

Nitrous oxide (laughing gas) - stable in atmosphere; accumulatingbecause natural breakdown processes are too slow to manage increased load.

NOx gases (NO, NO2) - soluble, acid-forming gases

Nitrogen is an important and significant component of organictissue. Proteins.

Organic matter can be characterized by its C/N ratio. Nitrogen-rich wastes, for example, will release soluble fixed nitrogen, and can be used as nitrogen fertilizers.

Nitrogen Cycle Unknowns:

What is the amount of nitrogen fixed annually in major biomes?How has this changed over time?(Think about where lots of carbon is fixed today.)

Are stores of fixed nitrogen in tilled soils being reduced? Whatabout tropical forest ecosystems?

What effect does anthropogenic nitrogen have on rivers andcoastal biomes? (coral reefs?)

What will be the stable concentration of nitrous oxide in theupper atmosphere?

Historic trends of NOx andSox emissions in the US.

What causes the two ‘dips’ in the SOx curve?

Ozone:

O3 - “Sharp-smelling, colorless gas”

O2 + O -> O3

Ozone intercepts UV in the 200-300 nm wavelength.

Historical Perspective:

By 600 mya, there was enough atmospheric oxygen (~10% PAL)to produce ozone in upper atmosphere. This was critical to thesubsequent evolution of life on land.

The ‘Ozone Layer’

At heights of 20-30 km in atmosphere

10 ppm vs. 0.04ppm in typical troposphere

90% of ozone in atmosphere

Protective ozone - intercepts UV

Ozone layer measured in Dobson Units (DU).

One DU = 2.69 x 1016 molecules/cm2

Bad Ozone:

Health hazard when inhaled

Strong oxidizing agent

Combines with gasoline compounds to form “photochemicaloxidants” which are common in urban smog

Summer - warm temperatures, air stagnation/stratification,slow-moving air masses

Ozone/oxidant-rich air masses may travel from urban to rural areas. Effects on vegetation and crops have been noted.

Ozone Production:

O2 + UV light -> 2 O

O + O2 -> O3

O3 + UV -> O2 + O

O + O2 -> O3

O3 + O -> 2O2

These are known collectively as the ‘Chapman Reactions”. In natural systems, there is an approximate balance between theproduction and destruction of ozone in the lower stratosphere, whichkeeps the level at about 300 DU

Ozone Destruction:

O3 + X -> XO + O2 (where X is O, NO, OH, Br, CL)

This process is accelerated by the presence of catalytic surfaces likeice crystals or dust particles.

CFC (Chloro-fluorocarbons) are an important source of Cl in the upper atmosphere.

CCl3 F - (CFC-11) Refrigerants, aerosol can propellantsCCl2F2 - (CFC-12) These break down to release Cl.

Cl + O3 -> ClO + O2

ClO + O -> Cl + O2

Ozone Depletion Poles:

Lower ozone production in winter

Ice crystals provided catalytic surfaces

Air trapped in polar vortex

30-50% reduction in ozone levels - the ozone ‘hole’(vs. 3-4% natural variation caused by sunspot cycles)

Increased UV reaches surface

Human health effects; changes in photosynthetic organisms; other unknown effects on biological systems

Global Ozone Agreements:

CFC Reductions - Replacement of CFC’s with other propellantsin aerosol cans

- Replacement of refrigerants; limitations on production

Supersonic Transport Aircraft (SST)- Proposed limits on flights at high altitudes.

Tropospheric Ozone:

Ozone produced by high-temperatures within internal combustion engines.

Ozone combines with photo-active compounds in smog.

Catalytic converters reduce (somewhat) pollution by ozone and smog components.

Oxygenated gasolines reduce output of photo-active compounds.

A few others:

Lead

VOC’s (volatile organic compounds)

Particulates

CFC’s (see ozone)

The carbon cycle

Three scales of cycling:

a. Short - photosynthesis/respirationdays-months-years

b. Intermediate - storage and removal offixed carbon from sedimentary rocks105 - 108 years

c. Long - organic carbon/carbonate rocks;subduction/CO2 release; weathering ofsilicates on land108 - 1010 years

Carbon cycle:

Can be constructed in many ways, but typically:

atmosphere is reservoir of interestquantify flows of carbon into and out of atmosphere

Carbon species - carbon monoxide, methane, ‘organic matter’,carbon dioxide, and many others

Most research focuses on carbon dioxide because of its role as a greenhouse gas

A traditional ‘cartoon’ model of the carbon cycle.

The ‘short’ and ‘intermediate’ cyclesFive primary fluxes/transformation processes

1. Photosynthesis2. Detritus decomposition3. Ocean cycling 4. Fossil fuel combustion5. Deforestation

1-3 are primarily natural 4-5 are primarily anthropogenic

Estimates of anthropogenic emission are easier to produce.1. Fossil fuel consumption2. Deforestation estimates from satellite imagery

A “box” model of the global carbon cycle