Changes in Atmospheric Chemistry

Geog410

Atmospheric composition

Air pollution:

change in the concentration of material (energy) in the air such that the modified content adversely affects the well-being of living things (collectively solid, liquid, and gases)

Causes:1. Natural: gas from marshes; smoke from range and forest fires; volcanic

activity; decay of vegetation. They become pollutants only when they are placed into atmosphere in abnormally large mounts.

LA is “bay of smoke” in 1542. Prevailing weather condition caused the smoke from scattered Indian fires to hang as a pull of pollution over the area. Some are carcinogenic (cancer pro).

EPA is responsible for monitoring and enforcing laws pertaining to environmental laws.

Pollution Standards Index (PSI): an air quality standard that uses the value of the pollution that occurs in the highest concentration in relation to natural air quality standards. Normal value is below 100; Above 100 is unhealthy.

2. Anthropogenic: sources is related to the specific pollutants.

Lists of atmospheric pollutants

1. particulates: soots and acid aerosols in the air. Thick and hazy, especially in summer. They impair the functioning of lungs, affect chronic respiratory illness: asthma (difficulty in breezing), bronchitis (inflamed throat), emphysema (enlarged air space). It has the third largest cause of death.

PM10: dust-sized particulates, smaller than 10 microns in diameter.PM2.5: finer-sized particulates, smaller than 2.5 microns in diameter.Sources: diesel trucks and buses; factory and electric utility smoke stacks; car exhaust;

burning woods; mining; construction.2. Carbon Monoxide: colorless, odorless and tasteless gas formed by incomplete

combustion of coal, fuel oil, and gasoline (automobiles). If above 100PPM (parts per million), headache and dizzy. Last for a few days and change to CO2.

3. Sulfur Compounds (SO2 and H2S)SO2: a heavy, pungent, colorless gas from coal burning, stays 10 days and combined

with water to form sulfuric acid.Sulfuric acid causes (1) plant leaves turn yellow; (2) dissolves limestone and marble; (3)

corrosive of iron and steel (4) reduce atmospheric visibility and block out sun light; (5) irritant to eyes and respiratory system and can be lethal

H2S: hydrogen sulfide from organic decay where there is not enogh O2 present to oxidize the organic material (swamps), rotten egg smell.

continue

4. Nitrogen Oxides (NOx)Caused by the combustion at high temperatures in automobile engines.NO2: has yellow-brown in color and a pungent sweet odor. Stays in

air for 3 days and becomes nitric acid (HNO3). It also contribute to acid rain and surface O3 production.

5. Surface Ozone: colorless and odorless except at very high concentrations. A major ingredient in smog.

From unburned petroleum hydrocarbons and nitrogen oxides from automobiles exhausts and fossil fuel power plants from automobile exhausts and fossil fuel power plants react in sunlight. Faster in hot summer days. It starts to from at about 10:00AM. Solar time, and break down after sunset.

It causes respiratory problem who exercise outdoors. Irritant to lungs and air passages (cough, chest pain, shortness of breath). In 1988, ground O3 level reached highest eastern states of Mississippi river, in California, and Texas.

6. Acid PrecipitationAcid rain is a phrase that applies to a process that results in deposition of acid on the surface of the earth

(PH value <5.6).Natural precipitation has PH of 5.6. A neutral solution has a PH of 7.0. For each unit the PH drops. The

acidity increases by a multiple of 10.It is caused by injection of SO2 or NO2 into atmosphere by coal-burning electric power plants. It can

transport by wind over a great distance before precipitates to the ground.

Significant events:In Great Britain, PH of 2.0 affected Norfolk and Lincolnshire in 1987 september. It corroded aluminum

instruments, kill leaves of trees, etc.Impacts: (1) Aquatic environment (fresh-water lakes): fish become endangered when the PH drops to about 5.5.

Most species of fish stop reproducing at PH level between 5.3-5.6; in high acidity, trace metals are dissolved in the water and collects in fish’s gills, they choke to death by straggle in their own mucus (aluminum); Acidy prevents fish from absorbing calcium and sodium. Lack of calcium weakens their borne structure and skeletons deformed and easily damaged. Lack of sodium causes convulsions which kill the fish (abnormally violent and involuntary).

Acid shock during spring snow melt. Sensibility of lake to acidification depends on their natural ability to neutralize the acid runoff into the lake. In regions where the parent rock is high in mineral salts such as calcium, magnesium, and phosphorous, the soli solution tends more toward alkaline and the salts neutralize the acid;

Lakes with igneous and metamorphic rocks containing lots of silicates are most sensitive to acid deposition. Water remains highly acidic

In the world, about 1000 lakes have become too acidic to support life, and several hundreds to have acid shock.

Impact of Acid precipitation, Continue

(2) Terrestrial systemDamage forest in North America. Acid rain and acid fog cause rapid die back

of forest around mountain Mitchell in North Caroline. Fogs has PH of 2.5-3.5; Spruce forest in Whiteface mountain in New York; 1/3 of forest in German are damaged from acid rain

(3) Human healthIn southern Ontario, atmospheric sulfate levels roses, hospital admittance

increases (illness related to pneumonia and asthma; Children’s emphysema (air filled expansion of tissue) and other respiratory diseases.

Health hazard in eating fish taken from streams and lakes with increased acidity. These fishes has high levels of aluminum, copper, lead, mercury and zinc. Aluminum linked to Alzheimer’s disease.

(4) StructuresLimestone and marble are soluble in acids. In Great Britain, acid dissolve the

exteriors of major historical buildings. Replacement cannot keep up with the damage rate. Status replace by fibreglasses.

7. Stratosphere Ozone and UV radiation

98% ozone is found at stratosphere (7-30miles). Most ozone is produced in tropical areas (where radiation is strong) and moves into polar region.

CFCs reacts with ozone.

• Antarctic Ozone Hole

later 1970s sept-oct (spring in southern hemisphere), hole appears in September when sunlight first reaches the region and ends in October when circulation brings summer warming over Antarctic. Lowest was observed in 1987 August and September.

Occur on polar stratospheric clouds (moisture condenses into ice crystals and form nitric acid crystals when air temperature is below -84°C (-119°F). When nitric acid crystals drop out of the stratosphere leaving behind the chlorine and bromine compounds and ice crystals. Each ice crystal provides a place for accelerated chemical reactions that begins when sunlight appears in spring, the warming increases the rate of chemical reactions and chlorine destroy O3 at a rapid rate.Montreal Protocol; in 1978 US banned on the use of compounds as aerosol propellants.

Reducing risk of skin cancer

Avoid sun between 10am-2pm (11am-3:00pm day light saving time); sunscreen rating of 15 provide protection from UVB and UVA; avoid tanning parlors (radiation is bad or worse than natural sunlight).

Factors increase air pollution

1. Topography: hills, building, mountain blocks air movement, so favors accumulation of pollutants produced locally

2. High air temperature: increases ozone and photochemical smog production

3. Inversion: stable atmosphere traps pollutants.

Profile of Atmosphere based on air temperature profile

Figure 3.2

1. TroposphereSurface to 18 km (11 mi)90% mass of atmosphereLapse rate: the rate of air temperature decreases with elevationNormal lapse rate – average cooling at rate of 6.4 C°/km (3.5 F°/1000 ft)

2. Stratosphere18 to 50 km (11 to 31 mi)Inversion: air temperature increases with elevationOzone maximum

3. Mesosphere50 to 80 km (30 to 50 mi)4. ThermosphereRoughly same as heterosphere80 km (50 mi) outward

Natural Processes of Air pollution removal

• Wind: disperse pollutants into upper atmosphere and spread into larger area to dilute them

• Rain and snow: dissolves into water and deposit to the ground