@electronic{www.opensense.ethz.ch,
   title       = {OpenSense}, 
   url         = {http://www.opensense.ethz.ch/trac/},
   biburl      = {https://puma.uni-kassel.de/url/dc506d816e3a25aead448b6b152a7ae3/stumme},
   keywords    = {air airprobe everyaware opensense quality sensors sitc},
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@electronic{aqicn.org,
   title       = {Beijing Air Pollution: Real-time PM2.5 Air Quality Index (AQI)}, 
   url         = {http://aqicn.org/city/beijing/},
   biburl      = {https://puma.uni-kassel.de/url/6b90de60e08a81c8d5ff2b947f442b59/stumme},
   keywords    = {air airprobe quality sensor},
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@electronic{www.eea.europa.eu,
   title       = {Status of black carbon monitoring in ambient air in Europe — European Environment Agency (EEA)}, 
   url         = {http://www.eea.europa.eu/publications/status-of-black-carbon-monitoring},
   biburl      = {https://puma.uni-kassel.de/url/638e82683efed66805b29ed6a4e51e05/stumme},
   keywords    = {air airprobe black carbon everyaware monitoring quality sitc},
   added-at    = {2013-12-12T16:11:06.000+0100},
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