Abstract
Abstract. Various atmospheric sources and sinks regulate the abundance of tropospheric formaldehyde (HCHO), which is an important trace gas impacting the HOx (≡ HO2 + OH) budget and the concentration of ozone (O3). In this study, we present the formation and destruction terms of ambient HCHO and O3 calculated from in situ observations of various atmospheric trace gases measured at three different sites across Europe during summertime. These include a coastal site in Cyprus, in the scope of the Cyprus Photochemistry Experiment (CYPHEX) in 2014, a mountain site in southern Germany, as part of the Hohenpeißenberg Photochemistry Experiment (HOPE) in 2012, and a forested site in Finland, where measurements were performed during the Hyytiälä United Measurements of Photochemistry and Particles (HUMPPA) campaign in 2010. We show that, at all three sites, formaldehyde production from the OH oxidation of methane (CH4), acetaldehyde (CH3CHO), isoprene (C5H8) and methanol (CH3OH) can almost completely balance the observed loss via photolysis, OH oxidation and dry deposition. Ozone chemistry is clearly controlled by nitrogen oxides (NOx ≡ NO + NO2) that include O3 production from NO2 photolysis and O3 loss via the reaction with NO. Finally, we use the HCHO budget calculations to determine whether net ozone production is limited by the availability of VOCs (volatile organic compounds; VOC-limited regime) or NOx (NOx-limited regime). At the mountain site in Germany, O3 production is VOC limited, whereas it is NOx limited at the coastal site in Cyprus. The forested site in Finland is in the transition regime.
Highlights
Formaldehyde (HCHO) is an important atmospheric trace gas which provides insight into various photochemical processes taking place in the Earth’s atmosphere
HCHO production paths are more diverse and include oxidation processes of almost any volatile organic compound (VOC), including acetone (CH3COCH3), methane (CH4), acetaldehyde (CH3CHO), methanol (CH3OH), isoprene (C5H8), methyl hydroperoxide (CH3OOH), ethene (C2H4) and many more, the majority of which are initiated by the OH radical during the day (Stickler et al, 2006; Wittrock et al, 2006)
We have analyzed the photochemical processes contributing to formaldehyde and ozone production and loss across Europe based on in situ trace gas observations during three different stationary field campaigns in Cyprus (CYPHEX in 2014), Germany (HOPE in 2012) and Finland (HUMPPA in 2010)
Summary
Formaldehyde (HCHO) is an important atmospheric trace gas which provides insight into various photochemical processes taking place in the Earth’s atmosphere It has both anthropogenic sources, such as industrial and vehicle emissions, and natural sources including, for example, biomass burning or volatile organic compound (VOC) precursors, with natural sources dominating in remote locations (Luecken et al, 2018; Anderson et al, 2017; Stickler et al, 2006; Wittrock et al, 2006; Lowe and Schmidt, 1983). Net production processes of formaldehyde, influence the HOx (HOx ≡ OH + HO2) budget, which, in turn, controls the atmospheric oxidizing capacity (Luecken et al, 2018) This includes the regulation of the atmospheric ozone (O3) abundance, a trace gas with adverse health effects for humans, animals and plants, leading to cardiovascular and respiratory diseases and the decrease in life expectancy (Nuvolone et al, 2018; Lippmann, 1989). Important to understand the processes influencing and contributing to HCHO and O3 formation and loss processes in the Earth’s atmosphere (see Figs. 1 and 2 for an overview of the reactions considered in this study)
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