Question: when was the problem of cfc's discovered
[{'answer': 'late 1970s', 'provenance': [{'wikipedia_id': '54910', 'title': 'Chlorofluorocarbon', 'start_paragraph_id': 37, 'start_character': 10, 'end_paragraph_id': 37, 'end_character': 20, 'bleu_score': 1.0, 'section': 'Section::::History.:Regulation.\n'}]}, {'answer': '1973', 'provenance': [{'wikipedia_id': '54910', 'title': 'Chlorofluorocarbon', 'start_paragraph_id': 37, 'start_character': 366, 'end_paragraph_id': 37, 'end_character': 370, 'bleu_score': 1.0, 'section': 'Section::::History.:Regulation.\n'}]}, {'answer': '1970s', 'provenance': [{'wikipedia_id': '54910', 'title': 'Chlorofluorocarbon', 'start_paragraph_id': 34, 'start_character': 816, 'end_paragraph_id': 34, 'end_character': 821, 'bleu_score': 1.0, 'section': 'Section::::History.:Commercial development and use.\n'}]}, {'answer': '1974', 'provenance': [{'wikipedia_id': '54910', 'title': 'Chlorofluorocarbon', 'start_paragraph_id': 37, 'start_character': 898, 'end_paragraph_id': 37, 'end_character': 902, 'bleu_score': 1.0, 'section': 'Section::::History.:Regulation.\n'}]}, {'provenance': [{'wikipedia_id': '54910', 'title': 'Chlorofluorocarbon', 'start_paragraph_id': 37, 'start_character': 0, 'end_paragraph_id': 37, 'end_character': 1278, 'bleu_score': 0.9590753693839521, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 3956187005225439667}, 'section': 'Section::::History.:Regulation.\n'}]}, {'provenance': [{'wikipedia_id': '54910', 'title': 'Chlorofluorocarbon', 'section': 'Section::::History.:Regulation.\n', 'start_paragraph_id': 37, 'end_paragraph_id': 37, 'meta': {'evidence_span': ['capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 60 ppt of CFC-11 over Ireland. In a self-funded research expedition ending in 1973,', "Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. After the development of his electron capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 60 ppt of CFC-11 over Ireland. In a self-funded research expedition ending in 1973, Lovelock went on to measure CFC-11 in both the Arctic and Antarctic, finding the presence of the gas in each of 50 air samples collected, and concluding that CFCs are not hazardous to the environment. The experiment did however provide the first useful data on the presence of CFCs in the atmosphere. The damage caused by CFCs was discovered by Sherry Rowland and Mario Molina who, after hearing a lecture on the subject of Lovelock's work, embarked on research resulting in the first publication suggesting the connection in 1974. It turns out that one of CFCs' most attractive featurestheir low reactivity is key to their most destructive effects. CFCs' lack of reactivity gives them a lifespan that can exceed 100 years, giving them time to diffuse into the upper stratosphere. Once in the stratosphere, the sun's ultraviolet radiation is strong enough to cause the homolytic cleavage of the C-Cl bond. In 1978, under the Toxic Substances Control Act, the EPA banned commercial manufacturing and use of CFCS and aerosol propellants. This was later superseded by broader regulation by the EPA under the Clean Air Act to address stratospheric ozone depletion.", 'Since the late 1970s, the use of CFCs has been heavily regulated because of their destructive effects on the ozone layer. After the development of his electron capture detector, James Lovelock was the first to detect the widespread presence of CFCs in the air, finding a mole fraction of 60 ppt of CFC-11 over Ireland.']}}]}]