An improved device for continuously measuring dimethyl sulfide and isoprene in the air and seawater

The oceanic short-lived trace gases, such as dimethyl sulfide (DMS) and isoprene, play important roles between the surface ocean and the lower atmosphere. Once emitted into the atmosphere, these gases were rapidly oxidized, and their by-products could influence the atmospheric physical and chemical properties by forming particles. However, it is still challenging to collect these trace gases data efficiently due to the lack of a fully automatic measurement method. Therefore, we improved our previous home-made purge and trap system, including the controlling system, purge vessel and heating and cooling device, for measuring DMS and isoprene in the air and seawater respectively. The parameters, such as purge flow, split ratio and heating power rate (for controlling desorption temperature), were investigated by coupling with a gas chromatography–mass spectrometry (GC–MS). Under the conditions of split ratio 8:1, heating power rate 85% and purge flow 50 mL min−1, the peaks and intensities of DMS and isoprene standards were found to be sharp and significant. The standard curves were also established with high linear correlations (R2 > 0.97). The system was reliable and stable with small uncertainty (<5%) and low detection of limit (0.1 ppb and 4 ppt for the DMS and isoprene respectively in air sample, 0.2 nmol L−1 and 6 pmol L−1 for the DMS and isoprene respectively in water sample). Finally, the developed measurement method was successfully used to continuously detect the seawater and air samples. It is anticipated that our method could be widely spread because there are still many labs employing the traditional low automatic purge and trap system.