<http://webisa.webdatacommons.org/296215892>	<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>	<http://www.w3.org/ns/prov#Entity> .
<http://webisa.webdatacommons.org/prov/257023879>	<http://www.w3.org/ns/prov#wasDerivedFrom>	<http://webisa.webdatacommons.org/296215892> .
<http://webisa.webdatacommons.org/296215892>	<http://www.w3.org/ns/prov#wasQuotedFrom>	<federalregister.gov> .
<http://webisa.webdatacommons.org/296215892>	<http://www.w3.org/ns/prov#value>	"However, in considering an appropriate level for a secondary standard to address adverse effects of PM 2.5 on visibility, the EPA concluded that the determination of a single national level was complicated by important regional differences influenced by factors such as background and current levels of PM 2.5, composition of PM 2.5, and average relative humidity." .