Retrievals of formaldehyde from ground-based FTIR and MAX-DOAS observations at the Jungfraujoch station and comparisons with GEOS-Chem and IMAGES model simulations

Abstract

Abstract. As an ubiquitous product of the oxidation of many volatile organic compounds (VOCs), formaldehyde (HCHO) plays a key role as a short-lived and reactive intermediate in the atmospheric photo-oxidation pathways leading to the formation of tropospheric ozone and secondary organic aerosols. In this study, HCHO profiles have been successfully retrieved from ground-based Fourier transform infrared (FTIR) solar spectra and UV-visible Multi-AXis Differential Optical Absorption Spectroscopy (MAX-DOAS) scans recorded during the July 2010–December 2012 time period at the Jungfraujoch station (Swiss Alps, 46.5° N, 8.0° E, 3580 m a.s.l.). Analysis of the retrieved products has revealed different vertical sensitivity between both remote sensing techniques. Furthermore, HCHO amounts simulated by two state-of-the-art chemical transport models (CTMs), GEOS-Chem and IMAGES v2, have been compared to FTIR total columns and MAX-DOAS 3.6–8 km partial columns, accounting for the respective vertical resolution of each ground-based instrument. Using the CTM outputs as the intermediate, FTIR and MAX-DOAS retrievals have shown consistent seasonal modulations of HCHO throughout the investigated period, characterized by summertime maximum and wintertime minimum. Such comparisons have also highlighted that FTIR and MAX-DOAS provide complementary products for the HCHO retrieval above the Jungfraujoch station. Finally, tests have revealed that the updated IR parameters from the HITRAN 2012 database have a cumulative effect and significantly decrease the retrieved HCHO columns with respect to the use of the HITRAN 2008 compilation.

NDACC harmonized formaldehyde time-series from 21 FTIR stations covering a wide range of column abundances

“…a positive bias of 30% or even 50% is found at Reunion Island if the settings of Franco et al (2015) or Jones et al (2009) are used, respectively, instead of those from Vigouroux et al (2009). Although these high biases are consistent with the uncertainty budgets, it is important, to facilitate the interpretation of a satellite or model validation, to harmonize the settings 20 among the stations.…”

“…no large residuals remain due to bad spectroscopic or incorrect ILS parameters). In the past studies, while the micro-window spectral widths differ, some common HCHO sig- were used in all previous stud-10 ies (Notholt et al, 1997;Paton-Walsh et al, 2005;Viatte et al, 2014;Jones et al, 2009;Vigouroux et al, 2009), except in Franco et al (2015) who discarded the 2781.0 cm −1 signature because of the bad residuals due to poorly fitted CH 4 lines (from HITRAN 2008, Rothman et al (2009). In Vigouroux et al (2009), in which HITRAN 2004(Rothman et al, 2005 was used, the micro-windows containing these two stronger signatures were quite narrow (2778.…”

“…This seems to be the case at Altzomoni, which lies in the same model pixel as Mexico City, leading to an overestimation of 26%, much larger in summer (+49%), and at the European station Zugspitze where the model overestimates the HCHO levels by +41%. Note that in the study of Franco et al (2015), a negative bias (-13%) was observed between FTIR at Jungfraujoch (47…”

“…We keep the two narrow micro-windows used in Vigouroux et al (2009) andFranco et al (2015) at about 2763.5 and 2765.8 cm…”

Retrieval of ammonia from ground-based FTIR solar spectra

“…For Jungfraujoch, the error computation was performed using the perturbation method, the spectra of 2009 to 2011 and the Rodger formalism as explained e.g. in Franco et al (2015). For Réunion Island, the covariance matrix used for the smoothing error has diagonal elements representing 150 % variability from the a priori profile.…”