IB Ess 6 4 Stratospheric Ozone Question Bank

oxygen \(/ \mathrm{O}_{2}\) B: nitrogen \(/ \mathrm{N}_{2}\); Both required to award [1]. Do not accept N or O.

ozone initially declined; b. ozone stabilized / began to increase slightly; Note: do not credit descriptions of the projected values. Allow 1 mark for overall decline Precise dates are not necessary for credit (i.e. accept change occurring around 2000). (b) State one chemical responsible for the trend in the recorded annually averaged data between 1980 and 1990 shown in Figure 2.

halons/CFCs/HCFCsHBFCs/ \(\mathrm{N}_{2} \mathrm{O}\) /methyl bromide/methyl chloroform/carbon tetrachloride/ chlorine/bromine: Note: do not credit HFCs/ODSs (c) Outline one impact of low concentrations of stratospheric ozone on humans.

a. cell damage/premature aging of skin / skin cancer; b. cataracts / eye damage; c. immune system suppression; (d) Identify the year that stratospheric ozone is predicted to return to 1980 levels in Figure 2.

Accept any year in range 2041-2043; (e) Describe two reasons for the projected change in ozone levels after 2020 in Figure 2.

a. Montreal Protocol resulted in unprecedented international cooperation to address loss of ozone (and its influence still continues); b. banned use of CFCs/ phasing out of CFCs/ ozone depleting substances /refrigerants/aerosols/recycling of refrigerants; c. alternatives to CFCs (HFCs/HCFCs) were developed reducing harm to ozone; d. education/awareness campaigns led to changes in consumer preferences; e. ozone reforms due to natural reversible chemical reactions/processes / ODSs eventually begin to break down/dissipate; (f) Outline one factor that may affect the reliability of the model projections in Figure 2.

ozone initially declined; b. ozone stabilized / began to increase slightly; Note: do not credit descriptions of the projected values Allow 1 mark for overall decline Precise dates are not necessary for credit (i.e. accept change occurring around 2000). (b) State one chemical responsible for the trend in the recorded annually averaged data between 1980 and 1990 shown in Figure 2.

halons/CFCs/HCFCsHBFCs/ \(\mathrm{N}_{2} \mathrm{O}\) /methyl bromide/methyl chloroform/carbon tetrachloride/ chlorine/bromine: Note: do not credit HFCs/ODSs (c) Outline one impact of low concentrations of stratospheric ozone on plants.

a. cell damage on leaves / reduced leaf size/reduced plant growth/ photosynthesis; b. reduced phytoplankton in oceans; (d) Identify the year that stratospheric ozone is predicted to return to 1980 levels in Figure 2. [1]

Accept any year in range 2041-2043; (e) Describe two reasons for the projected change in ozone levels after 2020 in Figure 2.

a. Montreal Protocol resulted in unprecedented international cooperation to address loss of ozone (and its influence still continues); b. banned use of CFCs/ phasing out of CFCs/ ozone depleting substances /refrigerants/aerosols/recycling of refrigerants; c. alternatives to CFCs (HFCs/HCFCs) were developed reducing harm to ozone; d. education/awareness campaigns led to changes in consumer preferences; e. ozone reforms due to natural reversible chemical reactions/processes / ODSs eventually begin to break down/dissipate; (f) Outline one factor that may affect the reliability of the model projections in Figure 2.

increased skin cancer/melanomas/skin aging/mutations; increased eye abnormalities/cataract/photo allergy/blindness; weakening of immune systems; disrupts plant growth / damage leaves thus reducing photosynthesis / loss of plant species; damage to phytoplankton in oceans / reducing base of food web; causes death of krill/zooplankton/amphibian larvae reducing diversity/food for higher trophic levels; Note: Do not give credit for responses simply stating it leads to increased UV (Q asks for impact on "life"). Do not credit responses identifying consequences linked to GW. (Increased UV has negligible DIRECT impact on GW ...however, INDIRECTLY, eg by reducing primary productivity, it may contribute to GW, but such an indirect link would need to be explicitly stated to gain credit).

clear evidence of successful reduction in CFC use/ozone depletion/size of ozone hole; protocol prompted production of alternatives to replace CFCs allowing smooth phase-out; financial assistance was offered to assist in phase out of CFCs (Multilateral Fund); demonstrated it was possible for governments to work multilaterally; led to changes in the behaviour of individuals and societies; very large number of signatories; secured binding environmental agreements/legal commitments with which countries/industries complied; there was a widespread/common acceptance/understanding of the effect of CFCs (amongst scientists/public/politicians); Note: Simply stating "CFCs were banned" or "banning of CFCs" is not sufficient for credit.

because HFCs are bad for climate/contribute to global warming; realisation that environmental issues need to be addressed at an intergovernmental level; realisation that changes in behaviour are necessary to protect the environment in the future; in response to development in scientific understanding of issue; rich countries agreed to provide financial assistance for poorer countries to phase out HFCs; because technological development has found alternatives to HFCs;

(peak of 175- lowest point of 73= ) 102(ppb); Accept 72 - 75 as lowest point, ie 100-103 (ppb). Units and working are NOT required for the 1 mark. (b) State two factors necessary for the chemical formation of ozone in the troposphere.

sunlight/UV light; NOx/oxygen (atoms/ free radicals/molecules)/hydrocarbons/VOCs; Note: Only credit necessary reactants for ozone formation as shown above. Do not credit sources of these active pollutants (eg fossil fuel use, organic solvents, pesticides etc). (c) Outline why a high concentration of ozone in the troposphere is a direct problem for humans, while in the stratosphere it is a benefit to humans.

in the troposphere it causes respiratory illnesses / eye/nose/throat irritations / heart failure; in the stratosphere it prevents entry of UV that is harmful to humans/can cause mutations/skin cancer/tissue damage/cataracts/crop damage; [1 max] Note: Do not credit responses that simply suggest global warming/climate change as an impact of tropospheric ozone without referring to some direct impact of those phenomena on humans. Note: Accept "ozone in stratosphere protects humans from UV" WTTE ... (use of "protects humans" implies UV is harmful to humans). d) Suggest possible reasons for the overall trends of tropospheric ozone levels in Figure 3.

in the (lower) stratosphere / over the poles / above the Antarctic/Arctic / at higher latitudes / Australia/NZ; (b) Describe the changes in mean ozone hole area between 1979 and 2016.

rapid increase during the 1980s/up to 1990s/ from 1979-87; reaches maximum in late 1990s; relative stable during late1990s; fluctuating from 2000 onwards; possibly declining in late 2000s/from 2014; Be prepared to give a little leeway in precise years for changes in trends, but some reference to their timing is required. (c) Identify one possible reason for the changes shown during the 1980s.

increasing use of/disposal of refrigerants containing CFCs; increasing use of CFCs in aerosols; increasing release of \(\mathrm{NO}_{x}\) from fossil fuel combustion; increasing use of methyl bromides as pesticides; Responses should identify the ODS and its use for full credit. (d) Explain how the data in Figure 3 can be used in judging the success of the Montreal Protocol in addressing ozone depletion.

Montreal Protocol was introduced in 1987/graph covers period before and after introduction of Montreal Protocol; it introduced a ban on the use of CFCs / led to use of alternative HCFs/HFs; rate of ozone destruction/growth of the ozone hole slows down/stops soon after this date; suggesting it had some success/favourable impact on ozone depletion; however, there is little evidence of ozone levels being restored to earlier levels / hole disappearing; possibly some evidence in last few years/2014-2016 on graph of ozone hole reducing/ozone being restored; the stabilisation/limited decline in ozone hole may suggest black market sale of ODSs (limited success); continued impact of long-lasting ODSs (CFCs/HCFs) delay final judgement; Part (c) questions in Section B are all to be assessed using the markbands on page 17 with the guidance given below for each question.

Introductory explanations: i. ozone depleting substances (ODSs)/CFCs disrupt (the dynamic equilibrium of) ozone formation; ii. ODSs are halogenated organic gases such as chlorofluorocarbons (CFCs) / halons; iii. ...used as cooling agents (old refrigerators, air-conditioning units) / aerosol propellants (spray cans) / blowing agents (insulating foams) / fire-extinguishers / cleaning solvents (electronic equipment) / pesticides; Activities that lead to increase/restoration of ozone: iv. pollution management may be achieved by reducing the manufacture and release of ozone-depleting substances; v. methods for this reduction include recycling refrigerants/developing alternatives to gas-blown plastics/ halogenated pesticides/propellants and aerosols/developing non-propellant alternatives; vi. the Montreal Protocol (on Substances that Deplete the Ozone Layer (1987)) (and subsequent updates) is an international agreement for the reduction of use of ODSs; vii. this is considered to be a very successful international agreement; viii. national governments complying with the agreement made national laws and regulations to decrease the consumption/production of ODSs; Mechanisms that lead to reduction/destruction of ozone: ix. UV light breaks apart the ODSs/CFCs and releases a halogen atom; x. ... halogen atom breaks an ozone molecule apart and combines with an oxygen atom; xi. oxygen atoms combine with the oxygen from the halogen and release the halogen to start the process again; xii. ... the halogen is considered a catalyst / why the reaction is cyclical; Explanations of "continuing" effect on ozone: xiii. ODSs/CFCs have a very long lifetime in the atmosphere / there is a time lag from removal of ODSs to the end of ozone destruction; xiv. halogen atoms are removed very slowly from stratosphere; (CI by a chemical reaction with methane forming hydrochloric acid) xv. an illegal market for ozone-depleting substances persists and requires consistent monitoring; xvi. some countries are still not complying with international agreements on bans; xvii. HCFCs may have lower ozone depleting potential, but still destroy ozone (not phased out before 2020); xviii. increasing GCC/GHGs affect polar weather conditions (increasing temperature difference between troposphere and cooler stratosphere), thus affecting the distribution of ozone (positively in 2019, negatively in 2020); (Note that this should be the only link with GCC accepted) Notes: Award [5 max] if there are no explanations of "continuing" effect on ozone. Accept CFCs as alternative to ODSs.

Gases involved: for GW are CO2/CH4/CFCs (whereas) for OD are halogen containing gases/CFCs/NOx; Human activities responsible: for GW are human causes are very diverse (whereas) for OD more limited; for GW include burning fossil fuels for transportation/agriculture/heating / rice culture / deforestation (whereas) for OD include refrigeration / spraying / cleaning electronics; Mechanism; for GW involves GHGs trapping more infra-red/heat (whereas) OD involves chemical breakdown of ozone molecules; for GW involves increase in mean global temperature (whereas) OD involves more UV passing through atmosphere; Distribution: GW occurs globally (whereas) OD is concentrated around the poles; OD is caused largely by MEDC activities (whereas) LEDCs make significant contribution to GW through deforestation/rice culture;

Stratospheric ozone Tropospheric ozone Change in concentration Increase Increase Cause of change in concentration: ban of ozone depleting substances (ODS)/CFCs; Montreal protocol; increased number of vehicles; increase in combustion of fossil fuels; increase in concentration of populations in urban areas/activities that produce air pollution; formation of photochemical smog; increase in release of hydrocarbons/VOCs and NOx (from burning of fossil fuels) that react in sunlight to form ozone; Impact on humans: less UV exposure / less biological damaging effects (e.g skin cancer and cataracts); irritating/destroys living tissues/materials / damage to crops or forests/ irritates the eyes/ respiratory problems /cancer; One mark for two or three correct responses and two marks for four correct responses. No marks for only one correct response. Do not accept only 'health problems'.

Weaknesses [3 max] after Montreal Protocol entered in effect ozone levels continued decreasing / stabilized for a few years before declining again; agreement of Montreal Protocol was not followed by an immediate response / the banning of ODS occurred in stages / not all countries initially participated in the Montreal Protocol; enforcing/policing implementation of the Montreal Protocol across all nations is difficult; following banning of ODS/Montreal Protocol a black market trade continued in these substances; Montreal Protocol did not stop further destruction of stratospheric ozone due to the long life spans of ODS; the effects of the Montreal Protocol will take a long time to occur and for the ozone hole to reduce; Strengths [3 max] the ozone hole stabilized between around 1993 and 2008; in 1988 ozone hole showed a significant decline/ results for 1988 are anomaly; in 2002 ozone hole showed a significant decline/ results for 2002 are anomaly; without the Montreal Protocol the ozone hole may have continued to increase at a faster rate/indefinitely/beyond 26.6 million \(\mathrm{km}^{2}\); Protocol has led to reduction in production/use of ODS (eg.CFCs); due to reduction in ODS, ozone levels are expected to recover in the future (eg some scientist predict that by 2080 ozone levels will return to 1950 levels/ by 2014 there were signs the ozone hole was starting to recover); referred to as the most successful international environmental agreement /first universally agreed Protocol/agreed by all nations; it provides a model/example for other global environmental protection initiatives; Credit quantification of data eg: ozone hole increased by around 5 million \(\mathrm{km}^{2}\) between 1987 and 2008 compared to about 10 million \(\mathrm{km}^{2}\) between 1980 and 1986; Appraisal / Conclusion [1 max] - clear statement which adequately considers both strengths and weaknesses of the Montreal Protocol and implies which side is stronger based on evidence provided. N.B An isolated statement eg "the Montreal Protocol has been successful" or an unjustified opinion eg "I think the Montreal Protocol has been successful" should not be considered as a valid appraisal/conclusion. The appraisal/conclusion must be supported/justified by points raised that have addressed both sides of the argument. Award max of 4 marks for responses that do not refer to the data.