Atmospheric Chemistry and Physics www.atmos-chem-phys.net 1680-7316 1680-7324 6 5 2006 10.5194/acp-6-1181-2006 http://www.atmos-chem-phys.net/6/1181/2006/ http://www.atmos-chem-phys.net/6/1181/2006/acp-6-1181-2006.html http://www.atmos-chem-phys.net/6/1181/2006/acp-6-1181-2006.pdf 1181 1184 2006-04-18 An improved inlet for precisely measuring the atmospheric Ar/N<sub>2</sub> ratio T. W. Blaine R. F. Keeling W. J. Paplawsky Scripps Institution of Oceanography, University of California, San Diego, La Jolla, CA 92093-0244, USA The atmospheric Ar/N<sub>2</sub> ratio is expected to be useful as a tracer of air-sea heat exchange, but this application has been hindered in part due to sampling artifacts. Here we show that the variability in &delta;(Ar/N<sub>2</sub>) due to thermal fractionation at the inlet can be on the order of 40-80 per meg, and we introduce the use of an aspirated solar shield that successfully minimizes such fractionation. The data collected using this new inlet have a mean diurnal cycle of 1.0 per meg or less, suggesting that any residual thermal fractionation effect is reduced to this level.