PREFIX schema: <http://qweb.cs.aau.dk/airbase/schema/>
PREFIX property: <http://qweb.cs.aau.dk/airbase/property/> 
PREFIX xsd: <http://www.w3.org/2001/XMLSchema#>
SELECT ?station (avg(?no2) as ?avgno)  WHERE {
	?obs schema:NO2 ?no2 .
    ?obs schema:station ?stationObj .
	?stationObj property:station ?station .
   	?stationObj schema:inCity ?cityObj .
    ?obs schema:year ?year .
	?year property:yearNum "2011"^^xsd:integer .
	?cityObj property:city ?city .
    ?obs schema:sensor ?sensor .
    ?sensor property:statisticShortName "Mean"^^xsd:string . 
	FILTER(?city = "AALBORG"^^xsd:string || ?city = "COPENHAGEN"^^xsd:string || ?city = "ARHUS"^^xsd:string || ?city = "ODENSE"^^xsd:string)
} GROUP BY ?station HAVING (?avgno > 16.5)