Observation of atmospheric oxygenitrogen ratio aboard a cargo ship using gas chromatography/thermal conductivity detector

摘要

Measurements of atmospheric O_2/N_2 ratio and CO_2 concentration have been used to analyze the —ΔO_2/ΔCO_2 ratio to obtain information on CO_2 sources, e.g., anthropogenic or terrestrial biogenic sources (respiration or wildfire). In this study we report on the development of a shipboard system for measuring atmospheric O_2/N_2 ratio by using the gas chromatography/thermal conductivity detector (GC/TCD) technique. The standard error for a one hour average (N = 6) is found to be ± 5 per meg (± 1 ppm). The shipboard measurements have been conducted since the end of September 2007 on the Voluntary Observing Ship TRANS FUTURE 5, a cargo ship sailing between Japan, Australia, and New Zealand every six weeks. Spatially, the observation covers latitudes between 41°S and 33°N over the western Pacific. Air masses with high CO_2 concentration are observed along the coastline of Australia and New Zealand. In more than two thirds of the cases (17 of 23 events) detected between September 2007 and July 2009, values of the —ΔO_2/ΔCO_2 ratio are less than 1.15, indicating dominance of biogenic sources (e.g., respiration or wildfire) of CO_2.