Air pollution part 2

pH ScaleAcids= compounds that donate H+ to a solution.

Bases= compounds that accept H+ from a solution. They may also remove H+ from solutions by donating OH-.

Differences between levels are 10-fold.

pH of 6 = 10 x 101 [H+]

pH of 5 = 10 x 102 [H+]

Acid Deposition• What it is: fallout of sulfuric

(H2SO4) and nitric acid (HNO3) as precipitation, or sulfate (SO4

2-) and nitrate (NO3

-) salts as particulate matter.

• Effects: – Ecosystems: changes pH of

soil and aquatic systems– Stuff: erodes statues and

stone buildings

Open Source

Types of acid deposition• Wet deposition= rain, snow, fog, cloud vapor of pH

5.6 or lower• Dry deposition= acidic particles like sulfate and

nitrate salts• Together they are acid deposition, or more commonly

called acid rain (pH <5.6)• Wet deposition tends to travel farther than dry.

Acid deposition: in-depth• Sources: power plants,

factories, smelting plants, vehicles

• Tall smokestacks reduce local pollution, but increase downwind pollution, sometimes 1000s of miles away (eg New England, from mid-west)

• Eastern US has precipitation of pH 4.4-4.7 on average. This is due to wind borne acidic compounds and urban areas with lots of vehicles.

www.sourcewatch.org

© Cornell University

Regional effects• Ecological

– Leaches nutrient ions from the soil– Releases (toxic) heavy metal ions bound to soil

particles into aqueous solution in the soil– Increases pH of water bodies to fatal levels for

animal life

• Human– Chronic respiratory diseases– Leach heavy metals into drinking water sources

• Bioaccumulation

– Damage to buildings, statues, metal finishes

Factors That Limit Organisms

• Organisms have a “range of tolerance” for numerous factors• pH, temperature, salinity, UV radiation, heavy metal

concentrations, etc…Figure 3-11Figure 3-11

Aquatic organisms and pH

• Where in the world is the most acidic precipitation?

• How can we prevent acid rain?

Asia (particularly China)

Ozone• O3

• Occurs naturally in the stratosphere.

3O2 + UV 2O3

• Good in stratosphere…why?• Stops 95% of harmful UV radiation!• Bad in troposphere!

Atmospheric (total) ozone is measured in Dobson Units (DU).

1 DU= a column of O3 0.01mm thick at 0ºC and 1 atm.

Normal concentration= 300 DU

Ozone in the troposphere

• Forms when NOx compounds from vehicle and industrial emissions react with VOCs.– Remember the photochemical smog equation?

• Exposure to high levels (>80 ppb for 8+ hours) leads to negative health effects:– Respiratory tract irritation– Flare-ups of asthma

• Chronic exposure is toxic to both animals and plants.

• Highest levels in the summer in urbanized areas.

Photochemical smog revisit • Formation requires cars and sunlight• Morning commuter traffic releases large amounts of NOx and VOCs• UV radiation promotes a series of reactions, that result in more than 100 chemicals• Ozone is the most abundant• Warmer temperatures increase the rate of reaction• Amount of smog peaks at noon when the sun rays are strongest. They dissipate and fall to zero after

midnight. Cycle starts over again in the morning.• Cities exacerbate the problem due to the heat island effect.

Threats to the "good" (stratospheric) ozone

• Ozone is split up when it reacts with molecules that contain hydrogen, nitrogen, chlorine, & bromine

• Some of these molecules are naturally occurring. Others are anthropogenic in origin.

• CFCs (chloroflourocarbons, aka freons) are the big culprit.– HBFCs, halons, methyl bromide, HCL, CCl4,

methyl chloroform are other ODCs• When stratospheric ozone is depleted

through these reactions, higher levels of harmful UV radiation make it to ground level.

© NASA

Health effects

• Increased sunburns

• Increased cataracts

• Increased incidences of skin cancers:– Squamous and basal cell (treatable, low

mortality rate)– Malignant melanoma (treatable if caught

early, but overall 25% mortality rate)– Tanning beds increase risk by 55%

CFCs• Remain in troposphere for long periods

(insoluble in water and unreactive) acting as greenhouse gases

• After 11-20 yrs, end up in stratosphere• Breakdown under more intense UV

radiation, releasing highly reactive Cl and F

• These reactive atoms break up ozone

Normal CFC interference

Reactions summary:

UV + CCl3F --> CCl2F + Cl

Cl + O3 --> ClO + O2

ClO + O --> Cl + O2

Historic data

Instruments on the ground (at Halley) and high above Antarctica (the Total Ozone Mapping Spectrometer [TOMS] and Ozone Monitoring Instrument [OMI]) measured an acute drop in total atmospheric ozone during October in the early and middle 1980s. © NASA

Antarctic ozone "hole"• Not actually a hole, just a really low

concentration of ozone.

• Usually, chlorine atoms react with other molecules that stabilize them, but the Antarctic atmospheric conditions are funky: polar vortex.– Clouds form in the winter from pulling

moisture in from surrounding area, trapping lots of Cl, etc. bad molecules.

– When UV light returns during the Antarctic spring (August-November), chlorine atoms are freed.

– Free chlorine atoms break up ozone in that same cycle we just talked about

– As Antarctica warms (through our winter) the reactions slow down.

(http://ozonewatch.gsfc.nasa.gov)

9/2010

12/31/2010

Ozone regulation

• Clean Air Act Amendments 1990, 1992– Limited the production and consumption of chemicals that

deplete stratospheric ozone– Required the phase out of the chemicals by 1995

• Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol for short).– International treaty initiated in 1987 finalized in 1999.– Countries (all in UN) agreed to phases out ozone depleting

chemicals . Goal was 2010.– If all countries follow through, the ozone layer could recover

by 2050.

September 24, 2006: Biggest ozone hole to date

(http://ozonewatch.gsfc.nasa.gov)

Acid deposition article

• What are the two types of acid rain?• What are the anthropogenic sources of each

acid rain?• What are the ecological effects of acid rain?

Give specific examples.• Why is sulfuric acid rain decreasing while

nitric acid rain is not?• What is a major, unregulated source of nitric

acid rain?