Environmental Project No. 2019, 2018

Hydrocarbon background levels in Denmark – outdoor and indoor air

22-06-2018

The objective of this study was to address a need for well-documented Danish background/ambient levels of hydrocarbon VOCs in outdoor and indoor air in residences, which can be used for vapour intrusion studies.

At sites with a subsurface petroleum hydrocarbon contamination, many of the specific compounds detected in the indoor air can originate both from outdoor air, internal sources in the building and from the contaminated subsurface through vapor intrusion. Hence, vapour intrusion studies at hydrocarbon contaminated sites are challenged by the task of distinguishing between the contribution from ambient sources, and the contribution from vapor intrusion.

It was concluded that background levels of benzene and TVOC have the potential to interfere with vapor intrusion studies, while background levels of other compounds are not expected to interfere with vapor intrusion studies. A median value for the background indoor concentration of benzene was calculated to 0,66 µg/m3 in November and 0,41 µg/m3 in May. The corresponding value for outdoor air was calculated to 0,50 µg/m3 in November and 0,28 µg/m3 in May. Both outdoor and indoor background concentrations of benzene exceed the Danish regulatory limit for (0,13 µg/m3 ) in >99% of the residences. The indoor background concentration of TVOC can be expected to exceed the Danish regulatory limit (100 µg/m3 ) in about 30% of uncontaminated Danish residences, but the general background concentration of TVOC in outdoor air cannot be expected to exceed the regulatory limit.

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