Measurement report: Photochemical production and loss rates of formaldehyde and ozone across Europe

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 summer time. 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 includes 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 (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.

Tropospheric ozone production and chemical regime analysis during the COVID-19 lockdown over Europe

“…Many different methods enable the determination of the dominant chemical regime, such as the use of the weekend ozone effect, which considers the response of O 3 to NO x reductions on weekends, or the ratio of HCHO to NO 2 , with various approaches from in situ observations, remote sensing and model simulations (e.g., Jin et al, 2020;Pusede and Cohen, 2012;Nussbaumer and Cohen, 2020;Duncan et al, 2010). We have recently shown that the fraction α of methyl peroxyradicals (CH 3 O 2 ) forming formaldehyde (HCHO) in correlation with ambient NO concentrations is capable of indicating the dominant chemical regime based on three different field campaigns across Europe in Finland (HUMPPA 2012), Germany (HOPE 2012 and Cyprus (CYPHEX 2014) (Nussbaumer et al, 2021). CH 3 O 2 formed from, for example, the oxidation of acetaldehyde (CH 3 CHO) or methane (CH 4 ) can either react with NO or OH radicals to form HCHO or undergo the competing reaction with HO 2 to form methyl hydroperoxide (CH 3 OOH).…”

“…For more details, please see Fig. 1 in Nussbaumer et al (2021). α CH 3 O 2 consequently depends on the ambient concentrations of NO, OH and HO 2 and the respective rate constants for the reaction with CH 3 O 2 , the latter of which were taken from the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation (2021).…”

“…Low values for α CH 3 O 2 with a high response to NO are an indicator for a NO x -limited regime, whereas high values for α CH 3 O 2 with little response to changing NO represent a VOC limitation (Fig. 11 in Nussbaumer et al, 2021). Investigating the dominant chemical regime is an important method for analyzing photochemical processes and air quality.…”

Tropospheric ozone production and chemical regime analysis during the COVID-19 lockdown over Europe

“…Jin et al (2020); Pusede and Cohen (2012); Nussbaumer and Cohen (2020); Duncan et al (2010)). We have recently shown that the share α of methyl peroxyradicals (CH 3 O 2 ) forming formaldehyde (HCHO) in correlation with ambient NO concentrations is capable of indicating the dominant chemical regime based on three different field campaigns across Europe in Finland (HUMPPA 2012), Germany (HOPE 2012) and Cyprus (CYPHEX 2014) (Nussbaumer et al, 2021). CH 3 O 2 formed from e.g.…”

“…the oxidation of methanol (CH 3 OH) or methane (CH 4 ) can either react with NO or OH radicals to form HCHO or undergo the competing reaction with HO 2 to form methyl hydroperoxide (CH 3 OOH). For more details, please see Figure 1 in Nussbaumer et al (2021). α CH3O2 consequently depends on the ambient concentrations of NO, OH and HO 2 and the respective rate constants for the reaction with CH 3 O 2 , the latter of which were taken from the IUPAC Task Group on Atmospheric Chemical Kinetic Data Evaluation (2021).…”