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 ?yearN (avg(?pm10) as ?avgpm10) WHERE {
     ?obs schema:PM10 ?pm10 .
     ?obs schema:station ?station .
     ?station property:longitudeDegree ?long .
     ?station property:latitudeDegree ?lat .
     ?station property:type "Background"^^xsd:string .
     ?station property:areaType ?class .
     ?obs schema:year ?year .
     ?year property:yearNum ?yearN .
     ?obs schema:sensor ?sensor .
     ?sensor property:statisticShortName "Mean"^^xsd:string . 
     FILTER (?class in ("suburban"^^xsd:string, "urban"^^xsd:string) && ?yearN >= 2000 && ?yearN <= 2014)
} GROUP BY ?yearN