Formic acid above the Jungfraujoch during 1985–2007: observed variability, seasonality, but no long-term background evolution

Abstract

Abstract. This paper reports on daytime total vertical column abundances of formic acid (HCOOH) above the Northern mid-latitude, high altitude Jungfraujoch station (Switzerland; 46.5 • N, 8.0 • E, 3580 m alt.). The columns were derived from the analysis of infrared solar observations regularly performed with high spectral resolution Fourier transform spectrometers during over 1500 days between September 1985 and September 2007. The investigation was based on the spectrometric fitting of five spectral intervals, one encompassing the HCOOH ν 6 band Q branch at 1105 cm −1 , and four additional ones allowing to optimally account for critical temperature-sensitive or time-evolving interferences by other atmospheric gases, in particular HDO, CCl 2 F 2 and CHClF 2 . The main results derived from the 22 years long database indicate that the free tropospheric burden of HCOOH above the Jungfraujoch undergoes important shortterm daytime variability, diurnal and seasonal modulations, inter-annual anomalies, but no significant long-term background change.A major progress in the remote determination of the atmospheric HCOOH columns reported here has resulted from the adoption of new, improved absolute spectral line intensities for the infrared ν 6 band of trans-formic acid, resulting in retrieved free tropospheric loadings being about a factor two smaller than if derived with previous spectroscopic parameters. Implications of this significant change with regard to earlier remote measurements of atmospheric formic acid Correspondence to: P. Duchatelet (p.duchatelet@ulg.ac.be) and comparison with relevant Northern mid-latitude findings, both in situ and remote, will be assessed critically. Sparse HCOOH model predictions will also be evoked and assessed with respect to findings reported here.

Five years of CO, HCN, C<sub>2</sub>H<sub>6</sub>, C<sub>2</sub>H<sub>2</sub>, CH<sub>3</sub>OH, HCOOH and H<sub>2</sub>CO total columns measured in the Canadian high Arctic

“…It presents a minimum in February of 1.05 × 10 15 molecules cm −2 . This is consistent with the study of Zander et al (2010), in which the seasonal modulation is in phase with biogenic emissions, which depend on solar isolation, local temperature, atmospheric transport and soil coverage. However, at Eureka, the HCOOH seasonal amplitude of 61 % is smaller than that of the other species, certainly due to the shorter lifetime of this molecule (three to four days; Table 1) as well as the importance of wet deposition as a sink.…”

“…Our HCOOH retrieved columns are in agreement in terms of mean and extreme values as well as seasonal amplitude, compared to those measured at Jungfraujoch (Zander et al, 2010). They reported a mean value of 1.70 ± 0.50 × 10 15 molecules cm −2 for June-July-August from 1985 to 2007, which is comparable to our average of 2.10 ± 0.20 × 10 15 molecule cm −2 for the same summer months from 2007 to 2011.…”

“…The spectroscopic parameters of this band have been updated (Perrin and Vander Auwera, 2007). Zander et al (2010) have shown that these improvements reduce the retrieved total columns by a factor of two. In this MW, a global SNR of 800 is used and interfering species (HDO,O 3 For H 2 CO, MWs are from Paton-Walsh et al (2005) where the lines belong to two bands, centred at 2782.000 and 2843.000 cm −1 , respectively.…”

“…For HCOOH, we use one MW between 1104.650 and 1105.600 cm −1 , which corresponds to the band used in Zander et al (2010), Paulot et al (2011) and . The spectroscopic parameters of this band have been updated (Perrin and Vander Auwera, 2007).…”

“…CH 3 OH and HCOOH have been measured in a limited number of ground-based FTIR studies (Paton-Walsh et al, 2005Rinsland et al, , 2009Zander et al, 2010;Paulot et al, 2011). The first FTIR data sets of H 2 CO were obtained in remote areas (Mahieu et al, 1997;Notholt et al, 1997a, b) and were then extended to urban areas (Hak et al, 2005) and the Southern Hemisphere (Jones et al, 2009;Vigouroux et al, 2009;Paton-Walsh et al, 2010).…”