HO<sub>x</sub> measurements in the summertime upper troposphere over Europe: a comparison of observations to a box model and a 3-D model

Abstract

Abstract. In situ airborne measurements of OH and HO 2 with the HORUS (HydrOxyl Radical measurement Unit based on fluorescence Spectroscopy) instrument were performed in the summertime upper troposphere across Europe during the HOOVER 2 (HO x OVer EuRope) campaign in July 2007. Complementary measurements of trace gas species and photolysis frequencies were conducted to obtain a broad data set, which has been used to quantify the significant HO x sources and sinks. In this study we compare the in situ measurement of OH and HO 2 with simulated mixing ratios from the constrained box model CAABA/MECCA (Chemistry As A Box Model Application/Module Efficiently Calculating the Chemistry of the Atmosphere), and the global circulation model EMAC (ECHAM5/MESSy Atmospheric Chemistry Model). The constrained box model reproduces the observed OH and HO 2 mixing ratios with better agreement (obs/mod median 98 % OH, 96 % HO 2 ) than the global model (median 76 % OH, 59 % HO 2 ). The observations and the computed HO x sources and sinks are used to identify deviations between the models and their impacts on the calculated HO x budget.

Chemical processes related to net ozone tendencies in the free troposphere

“…Additional flights in summer 2007 were directed to the Arctic (Svalbard, Norway; 78.1 • N, 15.3 • E) and two flights over central Germany to study the influence of deep convection. Details about the campaigns can be found in two previous publications (Klippel et al, 2011;Regelin et al, 2013).…”

The influence of deep convection on HCHO and H<sub>2</sub>O<sub>2</sub> in the upper troposphere over Europe

“…The mixing ratios of NO, O 3 and OH in the outflow are higher than in the inflow, while for HO 2 , HCHO and H 2 O 2 we find the reverse. The influence of the high NO on HO x partitioning has been addressed by Regelin et al (2013) and will not be discussed here. From the behaviour of the longer-lived, insoluble tracers, and assuming that the measurements in the boundary layer are representative of the in-flow of the thunderstorm cell, we infer that the convection transported nearly undiluted boundary-layer air into the UT.…”

“…In the present configuration, both the range and height maximum were reduced due to the use of two wing pods that housed additional instruments. The instrumentation consisted of a chemiluminescence detector (CLD 790 SR, ECO Physics, Switzerland) for NO, NO 2 and O 3 measurements (Hosaynali Beygi et al, 2011); a set of up-and downward looking 2π -steradian filter radiometers for j (NO 2 ) measurements (Meteorologie Consult GmbH, Germany); a quantum cascade laser IR-absorption spectrometer for CO, CH 4 and HCHO measurements (Schiller et al, 2008); a dual enzyme fluorescence monitor (model AL2001 CA peroxide monitor, Aero-Laser GmbH, Germany) to measure H 2 O 2 and organic hydroperoxides (Klippel et al, 2011); a laser induced fluorescence (LIF) instrument for simultaneous measurements of OH and HO 2 (Martinez et al, 2010;Regelin et al, 2013); a non-dispersive IR-absorption instrument (model LI-6262, LI-COR Inc., USA) for CO 2 and H 2 O measurements ; a proton transfer reaction mass spectrometer (PTR-MS, Ionicon, Austria) for partially-oxidized VOC measurements and a series of canisters for post-flight analysis of non-methane hydrocarbons (Colomb et al, 2006). Details about the instrument performance with respect to time resolution, precision, detection limit and total uncertainty can be found in Klippel et al (2011), Regelin et al (2013) and Bozem et al (2017).…”

“…Since both H 2 O 2 and HCHO are precursors of HO x radicals, transport of these species to the UT in convective clouds has a significant influence on the oxidizing capacity of the UT, since HO x production from photolysis of HCHO and H 2 O 2 typically exceeds primary OH production from O 3 photolysis and the subsequent reaction of O( 1 D) with water vapour (Jaeglé et al, 1997;Prather and Jacob, 1997;Lee et al, 1998;Wang and Prinn, 2000;Marie et al, 2003;Regelin et al, 2013;Lelieveld et al, 2016). Figure 1 illustrates the processes associated with deep convection.…”

“…Emphasis is given to HCHO, which has a medium solubility described by its Henry's law co- (Klippel et al, 2011;Regelin et al, 2013;Bozem et al, 2017).…”