Year-round retrievals of trace gases in the Arctic using the Extended-range Atmospheric Emitted Radiance Interferometer

Abstract

The Extended-range Atmospheric Emitted Radiance Interferometer (E-AERI) was installed at the Polar Environment Atmospheric Research Laboratory (PEARL) at Eureka, Nunavut, Canada in October 2008. Spectra from the E-AERI provide information about the radiative balance and budgets of trace gases in the Canadian high Arctic. Measurements are taken every 7 min year-round, including polar night when the solar-viewing spectrometers at PEARL are not operated. This allows E-AERI measurements to fill the gap in the PEARL dataset during the four months of polar night. Measurements were taken year-round in 2008–2009 at the PEARL Ridge Lab, which is 610 m a.s.l. (above sea-level), and from 2011 onwards at the Zero-Altitude PEARL Auxiliary Lab (0PAL), which is at sea level 15 km from the Ridge Lab. Total columns of O3, CO, CH4, and N2O have been retrieved using a modified version of the SFIT2 retrieval algorithm adapted for emission spectra. This provides the first ground-based nighttime measurements of these species at Eureka. Changes in the total columns driven by photochemistry and dynamics are observed. Analyses of E-AERI retrievals indicate accurate spectral fits (root-mean-square residuals consistent with noise) and a 10–15% uncertainty in the total column, depending on the trace gas. O3 comparisons between the E-AERI and a Bruker IFS 125HR Fourier transform infrared (FTIR) spectrometer, three Brewer spectrophotometers, two UV-visible ground-based spectrometers, and a System D'Analyse par Observations Zenithales (SAOZ) at PEARL are made from 2008–2009 and for 2011. 125HR CO, CH4, and N2O columns are also compared with the E-AERI measurements. Mean relative differences between the E-AERI and the other spectrometers are 1–10% (14% is for the un-smoothed profiles), which are less than the E-AERI's total column uncertainties. The E-AERI O3 and CO measurements are well correlated with the other spectrometers (r > 0.92 with the 125HR). The 24 h diurnal cycle and 365-day seasonal cycle of CO are observed and their amplitudes are quantified by the E-AERI (6–12 and 46%, respectively). The seasonal variability of H2O has an impact on the retrievals, leading to larger uncertainties in the summer months. Despite increased water vapour at the lower-altitude site 0PAL, measurements at 0PAL are consistent with measurements at PEARL.