Question: what factors led to the deadly smog in london in 1952
[{'answer': 'collected airborne pollutants', 'provenance': [{'wikipedia_id': '294378', 'title': 'Great Smog of London', 'start_paragraph_id': 1, 'start_character': 230, 'end_paragraph_id': 1, 'end_character': 259, 'bleu_score': 1.0, 'section': 'Section::::Abstract.'}]}, {'answer': 'A period of cold weather , combined with an anticyclone and windless conditions'}, {'provenance': [{'wikipedia_id': '294378', 'title': 'Great Smog of London', 'start_paragraph_id': 1, 'start_character': 0, 'end_paragraph_id': 1, 'end_character': 453, 'bleu_score': 0.97451705556073, 'meta': {'yes_no_answer': 'NONE', 'annotation_id': 18379995248117934468}, 'section': 'Section::::Abstract.'}]}]