Data for: Intercomparison of commercial analyzers for atmospheric ethane and methane observations

Methane (CH4) is a strong greenhouse gas that has become the focus of climate mitigation policies in recent years. Ethane / methane ratios can be used to identify and partition the different sources of methane, especially in areas with natural gas mixed with biogenic methane emissions, such as cities. We assessed the precision, accuracy, and selectivity of three commercially available laser-based analyzers that have been marketed as measuring instantaneous dry mole fractions of methane and ethane in ambient air. The Aerodyne SuperDUAL instrument performed best of the three instruments but it requires expertise to operate and space for the large footprint. The Aeris Mira Ultra LDS analyzer also performed well for the price point and small footprint but required characterization of the water vapor dependence of reported concentrations and careful setup for use. The Picarro G2210-i precisely measured methane but it did not detect the 10 ppbv increases in ambient ethane detected by the other two instruments when sampling a plume of incompletely combusted natural gas. For long-term tower deployments or those with large mobile laboratories, the Aerodyne SuperDUAL provides the best precision for methane and ethane. For smaller mobile platforms, the Aeris MIRA is a more compact analyzer, and with careful use, can quantify thermogenic methane sources to sufficient precision for short term deployments in urban or oil and gas areas. We weighed the advantages of each instrument, including size, power requirement, ease of use on mobile platforms, and expertise needed to operate the instrument, and we recommend the Aerodyne SuperDUAL or the Aeris MIRA Ultra LDS depending on the situation.

Methods
We collected data and assessed the precision, accuracy, and selectivity of three commercially available laser-based analyzers that have been marketed as measuring instantaneous dry-mole fractions of methane and ethane in ambient air. The instruments were calibrated against NOAA standards and the humidity correction was characterized and applied. We took the data reported by each analyzer and merged them into one file (EthaneIntercomp_Feb_merged_v20220802.RData). We also conducted stability tests by sampling compressed air and sampled ambient air outside. We analyzed the data in R using the script Commane_EthaneIntercomp_analysis_archive.R. The merged data file is output as merged_data.csv and contains raw, humidity corrected and final calibrated dry mole fractions of various trace gases. The readme guide is a text/R Markdown file.