Abstract
ABSTRACTContinuous formaldehyde measurements were performed at the high-altitude GAW site Environmental Research Station Schneefernerhaus for more than one year. This unique dataset was analyzed for daily and seasonal variation and for the influence of large-scale synoptic conditions and air-mass origin on the observed concentrations. The average daily course exhibited maxima in the afternoon and minima at night, however differing between seasons. The general strong seasonal variation with average values for winter, spring, summer, and fall of 0.350, 0.529, 0.986, 0.429 ppbv, respectively, could be well explained by secondary production following photochemical activity. The large variability of formaldehyde mixing ratios within the seasons was shown to be influenced by different factors in this complex topography such as mixing of air masses from the planetary boundary layer and the free troposphere, advection of differently aged air from various source regions, and local meteorological conditions. An analysis of the impact of large-scale weather types, cyclonality, and flow directions revealed that the cleanest air masses were advected from westerly directions in particular under cyclonic conditions while southerly cyclonic and northerly/northwesterly anticyclonic conditions led to the highest formaldehyde levels.
Highlights
Formaldehyde (HCHO) is a key substance in atmospheric chemistry, an important radical source in the remote free troposphere (FT), precursor of ozone (O3), and an important indicator of atmospheric photochemical activity
An analysis of the impact of large-scale weather types, cyclonality, and flow directions revealed that the cleanest air masses were advected from westerly directions in particular under cyclonic conditions while southerly cyclonic and northerly/northwesterly anticyclonic conditions led to the highest formaldehyde levels
The annual variation of HCHO background is primarily driven by photochemistry that is mainly dependent on solar radiation, producing the highest amounts of secondary HCHO from methane and other precursors during the summer months (Solberg et al, 2001)
Summary
Formaldehyde (HCHO) is a key substance in atmospheric chemistry, an important radical source in the remote free troposphere (FT), precursor of ozone (O3), and an important indicator of atmospheric photochemical activity. It is known as a human and animal carcinogen. Besides a broad range of anthropogenic VOCs that contribute to HCHO production, biogenic sources (e.g., ethene, isoprene) play an important role especially in rural and remote settings during the vegetation period (Duane et al, 2002; Millet et al, 2006; Guo et al, 2009; Luecken et al, 2012)
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