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Discussion papers
https://doi.org/10.5194/acp-2019-114
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/acp-2019-114
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 27 Feb 2019

Research article | 27 Feb 2019

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This discussion paper is a preprint. A revision of the manuscript is under review for the journal Atmospheric Chemistry and Physics (ACP).

Trends in N2O and SF6 mole fraction in archived air samples from Cape Meares, Oregon (USA) 1978–1996

Terry C. Rolfe and Andrew L. Rice Terry C. Rolfe and Andrew L. Rice
  • Department of Physics, Portland State University, Portland, 97201, United States

Abstract. Quantifying historical trends in atmospheric greenhouse gases (GHG) is important to understanding changes in their budgets and for climate modeling which simulates historic and projects future climate. Archived samples analyzed using updated measurement techniques and calibration scales can reduce uncertainties in historic records of GHG mole fractions and their trends in time. Here, we present historical measurements of two important GHG, nitrous oxide (N2O) and sulfur hexafluoride (SF6), collected at the midlatitude northern hemisphere station Cape Meares, Oregon (USA, 45.5° N, 124° W) between 1978 and 1996 in archived air samples from the Oregon Health and Science University–Portland State University (OHSU–PSU) Air Archive. N2O is the third most important anthropogenically forced GHG behind carbon dioxide (CO2) and methane (CH4). SF6 has a low abundance in the atmosphere, but is one of the most powerful GHG known. Measurements of atmospheric N2O made during this period are available for select locations but prior to mid-1990 have larger uncertainties than more recent periods due to advancements made in gas chromatography (GC) methods. Few atmospheric SF6 measurements pre-1990 exist, particularly in the northern hemisphere. The GC system used to measure N2O and SF6 concentrations in this work is designed to be fully automated, capable of running up to 15 samples per batch. Measurement precision (1σ) of N2O and SF6 is 0.16 % and 1.1 % respectively. Samples were corrected for detector response non-linearity when measured against our reference standard, determined to be 0.14 ppb ppb−1 in N2O and 0.03 ppt ppt−1 in SF6. The concentration of N2O in archived samples is found to be 301.5 ± 0.3 ppb in 1980 and rises to 313.5 ± 0.3 ppb in 1996. The average growth rate over this period is 0.78 ± 0.03 ppb yr−1 (95 % CI). Seasonal amplitude is statistically robust, with a maximum anomaly of 0.3 ppb near April and a minimum near November of −0.4 ppb. Measurements of N2O match well with previously reported values for Cape Meares and other comparable locations. The concentration of SF6 in analyzed samples is found to be 0.85 ± 0.03 ppt in 1980 and rises to 3.83 ± 0.03 ppt in 1996. The average growth rate over this period is 0.17 ± 0.01 ppt yr−1 (95 % CI). Seasonality is statistically robust and has an annual peak anomaly of 0.04 ppb near January and a minimum anomaly of −0.03 ppt near July. These are unique SF6 results from this site and represent a significant increase in SF6 data available during the 1980s and early 1990s at any location. The concentration and growth rate of SF6 measured compares well to other northern hemisphere measurements over this period. From these N2O and SF6 measurements, overall we conclude that sample integrity is robust in the OHSU–PSU Air Archive.

Terry C. Rolfe and Andrew L. Rice
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Status: final response (author comments only)
AC: Author comment | RC: Referee comment | SC: Short comment | EC: Editor comment
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Terry C. Rolfe and Andrew L. Rice
Terry C. Rolfe and Andrew L. Rice
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Short summary
We present 159 measurements of the atmospheric mole fraction of nitrous oxide (N2O) and sulfur hexaflouride (SF6) from historic archived air samples collected at Cape Meares, Oregon (USA, 45.5° N, 124.0° W) between 1978 and 1996. These measurements add significantly to the historical record of the atmospheric composition for these important greenhouse gases. Results provide an analysis of the average atmospheric concentration, growth rate, and seasonality for N2O and SF6 in the mid-latitude.
We present 159 measurements of the atmospheric mole fraction of nitrous oxide (N2O) and sulfur...
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