Despite studies indicating that the Golden Temple was getting damaged due to pollution by coal hearths, among other things, a part of the langar is still being cooked from firewood.
Links:
[1] http://admin.indiaenvironmentportal.org.in/news/little-effort-check-pollution-shrine-complex
[2] http://admin.indiaenvironmentportal.org.in/category/author/neeraj-bagga
[3] http://admin.indiaenvironmentportal.org.in/category/newspaper/tribune-new-delhi
[4] http://admin.indiaenvironmentportal.org.in/category/thesaurus/punjab
[5] http://admin.indiaenvironmentportal.org.in/category/thesaurus/amritsar-t
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/air-pollution
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/firewood
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/state-pollution-control-board-spcb-0
[9] http://admin.indiaenvironmentportal.org.in/category/thesaurus/indian-institute-technology-iit
[10] http://admin.indiaenvironmentportal.org.in/category/thesaurus/industrial-pollution
[11] http://admin.indiaenvironmentportal.org.in/category/thesaurus/vehicular-pollution
[12] http://admin.indiaenvironmentportal.org.in/category/thesaurus/environmentalists
[13] http://admin.indiaenvironmentportal.org.in/category/thesaurus/religious-places