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

In-situ airborne measurements of OH and HO₂ with the HORUS (<b>H</b>ydr<b>O</b>xyl <b>R</b>adical measurement <b>U</b>nit based on fluorescence <b>S</b>pectroscopy) instrument were performed in the summertime upper troposphere across Europe during the HOOVER 2 (<b>HO</b>x <b>OV</b>er <b>E</b>u<b>R</b>ope) 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 HO₂ with simulated mixing ratios from the constrained box model CAABA/MECCA (<b>C</b>hemistry <b>A</b>s <b>A</b> <b>B</b>ox Model <b>A</b>pplication/<b>M</b>odule <b>E</b>fficiently <b>C</b>alculating the <b>C</b>hemistry of the <b>A</b>tmosphere), and the global circulation model EMAC (<b>E</b>CHAM5/<b>M</b>ESSy <b>A</b>tmospheric <b>C</b>hemistry Model). The constrained box model reproduces the observed OH and HO₂ mixing ratios with better agreement (obs/mod median 98% OH, 96% HO₂) than the global model (median 76% OH, 59% HO₂). 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

Impact of acetone (photo)oxidation on HOxproduction in the UT/LMS based on CARIBIC passenger aircraft observations and EMAC simulations

“…Recently, Regelin et al . [] have shown that calculated HO x levels from EMAC in the upper‐troposphere (7–10 km) over Europe significantly underestimate observed levels by ~24% (OH) and ~41% (HO 2 ). Upon scaling the OH/HO 2 field by factors of 1.3/1.5 (scenario 3 ), while leaving all other parameters unchanged (Table ), R (Ac/O1D) decreases at most by ~ −3% 2.5 km above the TP in autumn.…”

Tropospheric Reaction Chemistry

“…On the other hand, the underestimate of the calculated concentrations of HO 2 is the same situation as in the polluted atmosphere, and suggests the presence of unknown reaction pathways from OH to HO 2 as will be discussed later. The three-dimensional simulations are also performed for such aircraft measurements of OH and HO 2 , to make comparison in the free troposphere (Sudo et al 2002;Zhang et al 2008;Regelin et al 2012). Figure 7.13 is an example by Sudo et al (2002).…”