Change of the light nonmethane hydrocarbon blank values in tap water by water pipe renewal works.

Abstract

We proposed a method to measure light nonmethane hydrocarbon content in the atmosphere using distilled water, which was heated and cooled down to room temperature, in 2015. However, tap water, which distilled water is made from, originally contains some amount of light nonmethane hydrocarbons and they are not completely removed by a distilling apparatus. Since it is necessary to carefully consider the pollution by a minute amount of organic matter particularly in organic geochemistry, knowing their content in tap water is very important.

In January 2015, waterpipes in a building of the National Institute of Advanced Industrial Science and Technology were replaced. We measured the blank values of light nonmethane hydrocarbons in the tap water before and after the renewal work. The value increased after the renewal work and then decreased gradually. But it did not recover to the prior level after half a year. The relation between the blank values and sampling intervals was also investigated. It is clarified that the longer the flushing interval is, the lower the blank value becomes. This means flushing a large volume of water before the use is effective to temporarily reduce the content of light nonmethane hydrocarbons.