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 ν6 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, CCl2F2 and CHClF2. The main results derived from the 22 years long database indicate that the free tropospheric burden of HCOOH above the Jungfraujoch undergoes important short-term 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 ν6 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 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.
Highlights
Numerous field investigations of volatile organic compounds in the boundary layer and through the free troposphere have been undertaken in situ and remotely during isolated, timelimited local as well as regional studies since the mid-1980s
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 ν6 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, CCl2F2 and CHClF2
Summary
Numerous field investigations of volatile organic compounds in the boundary layer and through the free troposphere have been undertaken in situ and remotely during isolated, timelimited local as well as regional studies since the mid-1980s (e.g., local ground-based background monitoring; measurements during natural and controlled savannah fires; related Atlantic and Pacific ship- and airborne campaigns; stratospheric balloon flights- and space-based solar observations) They indicate that HCOOH is, after acetic acid (CH3COOH), the most abundant global organic carboxylic acid present in the Earth’s atmosphere, in both gaseous and liquid phases (e.g., Talbot et al, 1988, 1990; Puxbaum et al, 1988; Andreae et al, 1988; Arlander et al, 1990; Klemm et al, 1994; Sanhueza et al, 1996; Kesselmeier and Staudt, 1999; Khare et al, 1999; Poisson et al, 2000; Legrand et al, 2003, 2004). Despite original findings acquired along these field investigations and related chemical studies in the laboratory, there remain numerous gaps in the observational datasets, preventing regional and global background emissions to be satisfactorily quantified and understood, difficult to be adequately modeled
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