Acid rain Acid Deposition Acid Deposition Wet Dry

Acid rain “Acid Deposition”

Acid Deposition Wet Dry Acid rain, fog, snow Acidic gases & particles

SOx: oxides of sulfur NOx: oxides of nitrogen THE SOURCE

Acid Deposition • Caused by: • Emissions of sulfur dioxide, nitrogen oxides & carbon dioxide –Fossil fuel combustion by automobiles –Electric utilities –Industrial facilities • Once airborne: • These pollutants can react w/water, oxygen, & oxidants to produce sulfuric acid & nitric acid • Pollutants leading to acid deposition can travel long distances, leading to political issues between states/countries

Effects of Acid Deposition • It limits the ability of lakes to support aquatic life • Can change p. H of water • Can leach Al out of soil/rock & into waterways, killing the fish by damaging their gills & disrupting their salt balance, water balance, breathing, and circulation • May damage trees & plants • Causes nutrient leaching from soil • H+ take place of important nutrients Ca, Mg & K • Causes insoluble forms of Al, zinc, mercury & copper into soluble forms, which can decrease water & nutrient uptake by plants • Leaves become discolored due to chlorosis (bleaching) & then die • More susceptible to pathogens & insects because weaker from rain • Damages agricultural crops • Erodes stone buildings (national monuments), corrodes cars, & erases writing from tombstones

• Sulfur Dioxide • NOx emissions • New technologies, like scrubbers, have decreased SO 2 emissions when burning fossil fuels • Have increased • But reduction is not enough

OZONE

Ozone, O 3 Good ozone • Bad ozone • 6 -30 miles above Earth’s surface (Stratosphere) • ABSORBS most of the Sun’s Ultraviolet-B & UV-C radiation • Provides critical protection because UV radiation is a mutagen & carcinogen • Destroyed by CFC’s • Montreal Protocol set up a time table for phasing out CFC’s & other ozone depleting substances • Troposphere • Formed when pollutants emitted by car exhaust, gasoline vapors, industrial facilities, electric utilities & chemical solvents react chemically in the presence of sunlight – NOx + Sunlight= ozone • Harmful air pollutant! • Part of photochemical smog – NOx/SOx + ozone + sunlight + VOCs= smog

GOOD OZONE Ozone is naturally created by the interaction of sunlight + atmospheric oxygen O 2 + UV (sunlight) --> O + O 2 --> O 3

Formation of stratospheric ozone

The Sun The sun emits: • High-energy ultraviolet waves • Medium-energy waves that we see as light • Lower-energy infrared heat waves

Stratospheric Ozone • Ozone layer in stratosphere blocks about 99% of the sun’s UV-B & UV-C radiation. – UV-A passes through atmosphere w/out being absorbed & contributes to, and possibly initiates skin cancer – UV-B & UV-C have enough energy to cause potentially significant damage to the tissues & DNA of living organisms • Can also: reduce primary productivity in oceans, disrupt food chains, cause widespread effects on major food crops, decrease plant productivity O 3 + UV-B or UV-C O 2 + O

Breakdown of stratospheric ozone

Breakdown of stratospheric ozone • Certain chemical catalysts, most notably chlorine, can break down ozone. • Chlorofluorcarbons (CFCs) – Man-made – Used in refrigeration & air conditioning – Propellants in aerosol cans, like deodorant or insect spray – Blowing agents to inject air into foam products like styrofoam cups and foam insulation – Stable, nontoxic, and nonflammable – Don’t break down, so they slowly circulate to atmosphere

Breakdown of stratospheric ozone • The CFC’s migrate to the upper stratosphere where the UV radiation breaks them apart, releasing chlorine atoms. CCl 3 F + UV Cl + CCl 2 F • The chlorine breaks ozone’s bonds & pulls off one atom of oxygen • Cl + O 3 Cl. O + O 2 • Then a free oxygen pulls the oxygen atom from Cl. O, freeing the chlorine & creating one more oxygen molecule – Cl. O + O Cl + O 2 • The free chlorine molecule is ready to break down more ozone!

Breakdown of stratospheric ozone Can also be broken down by: • NOx • Bromines & other Halons – Used as fumigants for soil pests such as termites • Carbon tetrachloride – Formally used as a cleaning solvent *They don’t reach stratosphere as efficiently as CFC’s because they are more reactive in the troposphere

Halons

Destruction of ozone • Mid-80’s scientists noticed that the stratospheric ozone in Antarctica had been decreasing each year • Depletion was greatest at the poles, but occurred worldwide

Destruction of ozone • In Antarctic, ozone depletion was seasonal – Depletion occurred from Aug-Nov – Late winter-early spring • Caused an area of severely reduced ozone concentrations over most of Antarctica (“ozone hole”)

Destruction of ozone • Winter conditions cause a build up of ice crystals mixed with NO, which creates stable Cl 2 • When sun reappears in Spring, UV radiation breaks down this molecule into Cl again, freeing it to catalyze the destruction of the ozone. – Ozone loss is greatest in the spring • As the air continues to warm, the natural production of ozone increases as more sunlight catalyzes the combination of oxygen back into ozone. – This occurs in Antarctica’s summer (Jan-Feb)

The Result • Decreased stratospheric ozone has increased the amount of UV-B radiation that reaches the Earth’s surface. – In mid-latitude N. America, UV radiation increased by 4% from 1979 -1992 – Increase is greater at the poles • UV radiation harms cells & can reduce photosynthetic activity of plants • Significant increases of skin cancer have increased, particularly in countries near the Antarctic ozone hole such as Chile & Australia

Efforts to reduce ozone depletion • 1987, 24 nations signed an agreement called the Montreal Protocol on Substances that Deplete the Ozone Layer • Committed to reducing reduce CFC production 50% by the year 2000 – Most far-reaching environmental treaty to date because global biosphere protection was prioritized over economic self-interest • Amendments eventually signed by 180 countries requiring the elimination of CFC production & use by 1996 – In total, protocol addressed 96 ozone-depleting compounds

The Result • Concentrations of chlorine in stratosphere has stabilized at about 5 ppb and should fall to 1 ppb by 2100 • Reduction process is slow because CFC’s are not easily removed from atmosphere

Bad Ozone & Photochemical Smog “EPA says half of the United States is Breathing Excessive Levels of Smog” Maximum allowable rate of O 3 is 0. 075 parts per million over 8 hours

Criteria Air Pollutants Compound Symbol Human-derived source Effects/Impacts Ozone O 3 A secondary • Reduces lung function & pollutant formed by exacerbates respiratory symptoms the combination of (harmful to respiratory tissue) sunlight, water, • - asthma, ephysema oxygen, VOCs, and NOx • Harmful to plant tissue • Damages materials such as rubber & plastic Causes: shortness of breath, pain when inhaling, wheezing/coughing, eye/nose irritation, interferes with body’s ability to fight off infection

Other Air Pollutants Compound Symbol Human-derived source Effects/Impacts Volatile organic compounds VOC Evaporation of fuel, solvents, paints; improper combustion of fuels such as gasoline (cars) • A precursor to ozone formation Volatile= easily evaporated at normal temperatures

Smog formation • The term "smog" was first used in London during the early 1900's to describe the combination of smoke and fog. • What we typically call "smog" today is a mixture of pollutants but is primarily made up of ground-level ozone. • Smog is often thought of as an urban problem but its not limited to these areas. Trees & shrubs produce VOCs that can contribute to photochemical smog, as do forest fires that begin naturally in rural areas.

Formation of ozone & smog • Part I: Takes place during the day, in the presence of sunlight –NO 2 + sunlight= NO + O 3 (ozone) • When VOCs are limited, the cycle of ozone formation & destruction generally takes place on a daily basis w/relatively small amounts of photochemical smog formation • Part II: When VOCs are present, they combine with nitrogen oxide to form photochemical oxidants • This causes a larger amount of ozone to accumulate because nitrogen oxide is no longer available to break down the ozone

Formation of ozone & smog PANs

Photochemical Oxidants • PANs • Peroxyacyl nitrates • Cause eyes to burn and damage vegetation

Atmospheric Temperatures affect formation of photochemical smog • Emissions of VOCs increase as temperature increases (evaporation) • NOx emissions increase as airconditioning demands for electricity on the hottest days • Ozone formation increases at higher temperatures