Air pollution part 2

Ozone• O3

• Occurs naturally in the stratosphere.

3O2 + UV 2O3

• Good in stratosphere…why?

• Bad in troposphere…why?

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

Threats to the "good" (stratospheric) ozone

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

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

CCl4, methyl chloroform are other ODCs

• What is the consequence of stratospheric ozone depletion?

© 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.

• Why so bad in 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

•Montreal Protocol on Substances that Deplete the Ozone Layer (Montreal Protocol for short).

•Clean Air Act Amendments 1990, 1992

September 24, 2006: Biggest ozone hole to date

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

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.

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?