# Chemical budgets of OH, HO2+RO2 and H2SO4 in a sub-urban temperate forest near Paris

Yang Jiao, Alexandre Kukui

► To cite this version:

Yang Jiao, Alexandre Kukui. Chemical budgets of OH, HO2+RO2 and H2SO4 in a sub-urban temper-
ate forest near Paris. EGU General Assembly 2025, Apr 2025, Vienna, Austria. 10.5194/egusphere-
egu25-17736 . insu-05202025

HAL Id: insu-05202025

https://insu.hal.science/insu-05202025v1

Submitted on 7 Aug 2025

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# Chemical budgets of OH, HO2+RO2 and H2SO4 in a sub-urban temperate forest near Paris

**Yang Jiao<fnref n="1" />, Alexandre Kukui<fnref n="1" />, and the ACROSS Rambouillet Measurements Team*

Understanding the OH and peroxy radical chemistry in different environments is essential to predict atmospheric lifetimes and chemical transformations of compounds emitted to the atmosphere of both biogenic and anthropogenic origin. The extent to which insight into radical chemistry can be gained by comparing simulated and measured radical concentrations has been found to depend on the environment. In particular, significant discrepancies between modeled and measured OH and peroxy radical concentrations have been observed in forested regions characterized by relatively high VOCs and low NO concentrations. The objective of this study was to assess the importance of different radical production and loss processes as well as the role of OH in the production of sulfuric acid, a major precursor of newly formed atmospheric particles, in a sub-urban temperate forest.

Measurements were performed as part of the ACROSS project (Atmospheric ChemistRy Of the Suburban foreSt) during June-July of 2022 at a forested site in Rambouillet located along the path of pollution plumes from Paris. OH radicals were measured in a forest clearing at ground-level (about 6 m). Co-located measurements of HO2+RO2 (i.e. the sum of hydroperoxy and organic peroxy radicals) and gas-phase H2SO4 were also made on top of a 40 m tower (~20 m above the forest canopy). A budget analysis was performed using steady-state calculations for OH and H2SO4 using other available measurements on the ground and on the tower (photolysis rates, NOx, O3, VOCs, OH reactivity, aerosol particle size distribution, etc.). A detailed budget analysis for OH and peroxy radicals was performed with a box-model using a MCM derived mechanism.

Calculated daytime and nighttime OH concentrations on the ground, using measured OH reactivity, showed good correlation with the measurements and reproduced the observed daytime maximum and nighttime levels of about 4×10⁶ molecule cm⁻³ and (2-6)×10⁵ molecule cm⁻³, respectively. The production of OH radicals in the clearing and above the canopy during the day was found to be dominated by its regeneration in reactions of HO₂ and RO₂ with nitric oxide. During the night, the ozonolysis of monoterpenes was a significant OH production pathway with its contribution depending on the nighttime NO concentrations. The box-model resulted in significant underestimation, up to a factor of two in daytime OH and an overestimation of OH reactivity. At the same time, the model sum of peroxy radicals was larger than measurements, especially during the night with lowest observed NO concentration. However, most of the time the model reproduced the observed peroxy radical temporal behavior on the ground and above the canopy, as well as their slightly lower concentrations over the canopy during the day.

<footnote n="1">¹Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), CNRS, Orléans, France</footnote>

<footnote>*A full list of authors appears at the end of the abstract</footnote>
The formation of H2SO4 was observed every day during the measurement period, with the median maximum H2SO4 concentration of 2.5×106 molecule cm⁻³ similar to that observed at some other forested sites. The calculated and measured daytime H2SO4 concentrations were highly correlated with formation of sulfuric acid via SO₂+OH reaction accounting for (90±20)% of the observed H2SO4.

**ACROSS Rambouillet Measurements Team:** Chaoyang Xue(1) ch.xue@mpic.de, Sebastien Dusanter(2) sebastien.dusanter@imt-lille-douai.fr, Ahmad Lahib(2) ahmad.lahib@imt-nord-europe.fr, Alexandre Tomas(2) alexandre.tomas@imt-nord-europe.fr, Marina Jamar(2) marina.jamar@imt-nord-europe.fr, Espéranza Perdrix(2) esperanza.perdrix@imt-nord-europe.fr, Pablo Espina Martin(3) pabesp@ceh.ac.uk, Max R. McGillen(4) max.mcgillen@cnrs-orleans.fr, John N. Crowley(5) john.crowley@mpic.de, Jan Schuladen(5) jan.schuladen@mpic.de, Stéphanie Alage(6) emoussa@lisa.ipsl.fr, Vincent Michoud(6) vincent.michoud@lisa.ipsl.fr, Manuela Cirtog(7) manuela.cirtog@lisa.ipsl.fr, Paola Formenti(6) paola.formenti@lisa.ipsl.fr, Claudia Di Biagio(6) claudia.biagio@lisa.ipsl.fr, Chenjie Yu(6) chenjie.yu@lisa.ipsl.fr, Hichem Bouzidi(6) Hichem.Bouzidi@lisa.ipsl.fr, Christopher Cantrell(7) christopher.cantrell@lisa.ipsl.fr, Coralie Schoemaecker(8) coralie.schoemaecker@univ-lille1.fr, Nesrine Shamas(8) nesrine.shamas@univ-lille.fr, Sébastien Batut(8) sebastien.batut@univ-lille.fr, Amaury Lahccen(8) amaury.lahccen@univ-lille.fr, Eric Villenave(9) eric.villenave@u-bordeaux.fr, Emilie Perraudin(9) emilie.perraudin@u-bordeaux.fr, Pierre-Marie Flaud(9) pierre-marie.flaud@u-bordeaux.fr, David O. De Haan(10) ddehaan@sandiego.edu, Kanuri I. Roundtree(10) kroundtree@sandiego.edu, Cyrielle Denjean(11) cyrielle.denjean@meteo.fr, Jean-Claude Etienne(11) jean-claude.etienne@meteo.fr, Olivier Garrouste(11) olivier.garouste@meteo.fr, Morgan Lopez(12) morgan.lopez@lsce.ipsl.fr, Valéry Catoire(1) valery.catoire@cnrs-orleans.fr, Laboratoire de Physique et Chimie de l'Environnement et de l'Espace (LPC2E), CNRS, Orléans, France, 2 Centre for Energy and Environment, IMT Nord Europe, Institut Mines-Télécom, Université de Lille, Lille, 59000, France, 3 UK Centre for Ecology and Hydrology, Bush State, Penicuik, EH26 0QB, UK, 4 Institut de Combustion, Aérothermique Réactivité et Environnement (ICARE), CNRS, 45071 Orléans, France, 5 Atmospheric Chemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany, 6 Université Paris Cité and Université Paris-Est Créteil, CNRS, LISA, 75013 Paris, France, 7 Université Paris-Est Créteil and Université Paris Cité, CNRS, LISA, 94010 Créteil, France, 8 Physico-Chimie des Processus de Combustion et de l'Atmosphère-PC2A, Université de Lille, CNRS, UMR 8522, Villeneuve d'Ascq, 59650, France, 9 Université Bordeaux, CNRS, EPOC, EPHE, UMR 5805, F-33600 Pessac, France, 10 Department of Chemistry and Biochemistry, University of San Diego, 5998 Alcala Park, San Diego, California 92110, United States of America, 11 CNRM, Université de Toulouse, Meteo-France, CNRS, 31057 Toulouse, France, 12 Laboratoire des Sciences du Climat et de l'Environnement (LSCE-IPSL), UMR CEA-CNRS-UVSQ, Gif-sur-Yvette, France