Laser based systems for gases and water isotopes

Every gas-phase molecule (e.g. CO2, CH4, or water vapor) has a unique absorption spectrum which can be used to measure its abundance in natural or experimental systems. Picarro has developed laser-based instruments that can measure trace gases and water vapor fast and accurately with equipment that is sufficiently robust to be carried to the field.  At the Centre for Ice and Climate we take advantage of this emerging technology. Starting in 2009, several laser based systems will be brought to the NEEM field camp to measure trace gases and water vapor.

About 10% of the volume of a polar ice core is air of atmospheric origin (read more about how air is trapped in ice cores here). Discrete measurements for e.g. the CH4 concentration are traditionally done by melting or crushing the ice followed by gas chromatography analysis of the released air. As a part of the impurity measurements carried out e.g. as part of the current NEEM deep drilling project, ice is continuously melted for chemical analyses. For these so- called Continuous Flow Analysis (CFA) measurements, the air bubbles in the ice are an annoyance, and the air in the sample stream is therefore removed without being used scientifically. We are working on techniques to measure the CH4 concentration of this air with a standard Picarro instrument. This will result in a CH4 record of unprecedented resolution that can be interpreted in connection with other high resolution climate records.

Another opportunity for online measurements in connection with the CFA system is water isotopes. For decades, the isotopic composition of the water (a proxy for the local temperature) has been measured by mass spectrometry. Obtaining a detailed water isotope profile is a labor intense and costly task. The Picarro instrument allows measurement of oxygen and hydrogen isotope compositions with a very high resolution but with lower accuracy than when using a mass spectrometer. A fraction of the continuous melt water stream is evaporated and the isotopic composition of the water vapor is measured in the Picarro instrument. The advantage is that the measurements can be done in the field with no further sample preparation than what is already required for the CFA measurements.

Read more about mass spectrometer water isotope measurements at Centre for Ice and Climate and about the Picarro laser absorption instrument (opens in a new window).