envsci 101 - Ozone in the atmosphere
A severe decrease in the concentration of ozone in the ozone layer could lead to the following harmful effects:
- An increase in the incidence of skin cancer (ultraviolet radiation can destroy acids in DNA). - A large increase in cataracts and sun burn - Suppression of immune systems in organisms - Adverse impact on crops and animals - Reduction in the growth of phytoplankton found in the Earth's oceans - Cooling of the Earth's stratosphere and possibly some surface climatic effect.
Hole keeps growing (on average 3% a year)
- No correlation? - Lag in response? - Irreversible damage? - Something else causing it? >Decreases in CFC's due to Montreal however increase in other pollutants (HFC's)
Scattering
The process of scattering occurs when small particles and gas molecules diffuse part of the incoming solar radiation in random directions without any alteration to the wavelength of the electromagnetic energy
What caused ozone hole?
Based on 25 years of previous data and hypotheses, the following was thought: • Not observed prior to 1980s • An hypothesis is proposed that this is caused by increased emissions of CFCs from Freon in aerosol spray and refrigerating systems, fertilisers, and nitrous oxides from jet exhausts were likely to explain destruction of ozone hole.
Colour of photochemical smog
Brown/yellowish. Temperature inversion traps ozone city smog over North American and European cities
Peaks of ozone on eastern seaboard
Collecting of pollutants from southern and westerly cities on eastern seaboard coupled with pollution produced locally results in high amounts of ozone pollution in this region
Auckland ozone concentration
Has low concentration not due to UV radiation (lots of), but we don't have other volatile organic compounds in atmosphere
Is ozone good or bad?
It's all a question of scale! ... WHERE is it? ... troposphere or stratosphere? in boundary layer it is formed as a secondary pollutant ... natural or anthropogenic (bad, secondary pollutant)?
Ozone Air Pollution at the surface
Ozone is a powerful oxidant and thus has both direct & indirect consequences on human life Ozone can: • inflame and damage the lining of the lung • reduce lung function • aggravate asthma • damage leaves & reduce crop yields • attack rubber and other man made substances
Ozone
Ozone is very good at absorbing incoming solar radiation in the ULTRA VIOLET wave band... - Protects the earth surface from high levels of UV radiation - Warms the stratosphere
Antarctic and artic ozone holes
Vary spatially from year to year >This can be due to a number of reasons including reading variability etc
Why do we mainly see the hole in winter in the Antarctic?
• Presence of polar stratospheric clouds, rich in nitrogen, and sunlight facilitates a series of reactions which prolong the life of chlorine • These clouds require very cold air (~ -85° Celsius) • Stratospheric air of this temperature occurs above Antarctica in the winter and early spring months • Destruction of the ozone begins in Antarctica in the spring as this region moves from 24 hours of night to 24 hours of day • These clouds are less frequent in the Arctic stratosphere because winter cooling of the air in the stratosphere is less severe.
Chlorine and ozone
• 1 mole of chlorine can destroy up to 100,000 moles of O3 • It is not destroyed in the reaction • Other compounds such as NO. and HO. also play an important role in destroying ozone -Found in CFC's
Surface ozone in Auckland
• 10-20 ppb (5-12ppb in Christchurch) • Maximum Auckland ~80 ppb (ChCh 40 ppb, LA 300 ppb!) • Isolation of city means long range transport unlikely • Re-circulation possible >Not a problem in AKL
What is ozone?
• A form of oxygen in which three atoms of oxygen occur together - O3 • Unstable & chemically active and has a short average lifetime in the atmosphere
Ozone measurement stats
• A reduction of about 3 % per year has been measured for Antarctica where most of the ozone loss is occurring globally since measurements began! • In some years, spring levels of stratospheric ozone were more than 50 % lower than the levels recorded months prior to the seasonal development of the hole.
Discovering of ozone layer thinning
• At first scientists didn't believe the data they saw! - instruments were faulty? - TOMS data? • Required repeat measurements and data from different sources to believe what they saw! • Developed a hypothesis as to why there was a hole which hadn't been seen before...
Causes of the 'hole'
• CFCs were created as a replacement to the toxic refrigerant ammonia • CFCs have also been used as a propellant in spray cans, cleaner for electronics, sterilant for hospital equipment, and to produce the bubbles in styrofoam • CFCs are cheap to produce and are very stable compounds, lasting up to 200 years in the atmosphere. • By 1988, some 320,000 metric tons of CFCs were used worldwide. -CFC's peaked in 1980's and 1990's, this was then stopped in international agreements (Montreal protocol) leading to a decrease in ozone layer
How do we know there is a HOLE??
• Dobson ozone spectrometer (since 1920s) - discovered ozone • In situ using balloons, aircraft (1970s) • Satellite images (NASA, NOAA, since 1960s) >First reported: BAS 1985
Ozone near the surface
• In the troposphere ozone is not emitted directly but formed as a secondary pollutant • It is formed as a result of the photo dissociation of NO2 >This reaction needs UV radiation (during day) and is much more efficient if volatile organic compounds are also present • The warmer the atmosphere the faster the formation of ozone • It is largely formed downwind of urban areas which have high vehicle emissions > It is therefore a regional scale problem (not likely to be isolated to one location)
Ozone concentrations
• Natural background (pre-industrial): 10-20 ppb • Remote locations in the Northern Hemisphere: 20-40 ppb (varying by season and latitude) • Rural areas during region-wide pollution events 80- 100 ppb • Peak O3 in urban areas during pollution events 120- 200 ppb • Maximum urban O3 (Los Angeles, Mexico City) 490 ppb • Stratospheric ozone layer 15000 ppb • US EPA health standard for ozone 125 ppb, 1-hour exposure (proposed revision: 85 ppb, 8 hour exposure)
Ozone in the stratosphere
• Naturally occurring (sun radiation changing oxygen molecules) • Much higher concentrations (15000 compared with a few hundred) • Layer of high concentrations of ozone (O3) molecules in the Earth's atmosphere. - 5 to 50 km above the surface - maximum concentration in the stratosphere at an altitude of approximately 25 km.
Reflection
• Reflection is a process where sunlight is redirected by 180 ° after it strikes an atmospheric particle. • This redirection causes a 100 % loss of the insolation. • Most of the reflection in our atmosphere occurs in clouds by particles of liquid and frozen water. • The reflectivity of a cloud can range from 40 to 90 %.
Atmospheric Effects on Incoming Solar Radiation
• Scattering • Reflection • Absorption • Re-emission
Absorption and emission
• Some gases and particles in the atmosphere have the ability to absorb incoming insolation • Absorption is defined as a process in which solar radiation is retained by a substance and converted into heat energy • That energy is then reemitted- but because the atmosphere is much cooler than the sun the radiation emitted is LONGWAVE
Key points
• Understanding temporal and spatial scale is important to determining whether a substance is a pollutant • In the troposphere high ozone concentrations cause human health problems and environmental damage • Ozone in the troposphere is formed as a result of chemical reactions of other pollutants : it is a secondary pollutant • Ozone in the stratosphere is normal and natural: it is the absence of ozone that is of concern • CFC's and other pollutants are thought to destroy ozone and cause the ozone hole • Low concentrations of ozone in the stratosphere have health and environmental implications for us particularly in NZ! But: • Ozone has only been measured since the 1970's and across the globe since the 1980's. - What is NORMAL? - What is natural? - Is it really caused by CFC's?
