Iodine Fate in Atmospheric Droplets: Heterogeneous

**IODINE FATE IN ATMOSPHERIC DROPLETS: HETEROGENEOUS REACTIVITY AND ROLE OF INTERFACE**:

- Réf
- **ABG-113442**
- Sujet de Thèse- 14/04/2023- Contrat doctoral- Institut de Radioprotection et de Sûreté Nucléaire- Lieu de travail- Cadarache - Provence-Alpes-Côte d'Azur - France- Intitulé du sujet- IODINE FATE IN ATMOSPHERIC DROPLETS: HETEROGENEOUS REACTIVITY AND ROLE OF INTERFACE- Champs scientifiques- Chimie

**Description du sujet**:
CONTEXT

**Since the late 90’, the fate of tropospheric iodinated species aroused the interest of atmospheric chemistry community but has also gained much interest in the field of nuclear safety**. Indeed, in case of incident or accident in a nuclear power plant or in a radioisotope production facility, the release of gaseous radioiodine compounds to the atmosphere must be considered. The knowledge of its reactivity is a key issue to predict its dispersion for **efficient current accident management plans.** The importance of halogens (Cl, Br) in the atmospheric compartment is well established since many decades - especially for their oxidative reactivity and their implication in the ozone budget control. The iodine chemistry in the atmosphere received increasing interest since the late 1990’s, and large progresses have been achieved regarding gas phase (photo)reactivity and the formation of iodine-containing aerosols. However, **heterogenous reactivity of iodine gases remains still poorly documented**. This gap prevents the **achievement of a comprehensive atmospheric iodine model**. In that context, the main objective of this PhD project is to contribute to **a better modeling of the global iodine cycle in the atmosphere by filling the gap in the heterogeneous reactivity of iodine in focusing on inorganic iodine interaction with aqueous phase.** The originality of the project lies in laboratory experimental **studies of iodine heterogeneous reactivity at the single particle scale**.

RESEARCH PROGRAM

The PhD project is divided in two complementary parts:
**1- (at IRSN-Cadarache)** **Determination of the uptake coefficients of gaseous inorganic iodine (I**2** and HOI) by aqueous droplets** as models of atmospheric aerosols. Laboratory experimental studies of gas-aerosol interaction will be conducted under controlled conditions using **open droplet train flow reactor** that is commonly employed to determine gaseous uptake coefficients The **role of droplets composition** will be investigated with respect to I2 and HOI uptake: (i) pure water reference case, (ii) including carboxylated compounds (formic acid, oxalic acid) may contribute to the release of stable iodinated organic volatile compounds into the atmosphere (CH3I for instance) and (iii)inorganic salts (NaCl, (NH4)2SO4, NaSO4, NaNO3 and NH4NO3) potentially impacting reactivity. These compounds are representative of organic and inorganic loading of atmospheric aerosols. State-of-the art detection techniques that include gas chromatography and mass spectrometry will be used to monitor on-line the reactant concentration and/or the formed reaction products in liquid phase at low level of detection. Thus, iodine uptake coefficients and composition evolution of particles will be addressed. The **influence of the particle size** will be explored with the generation of particles ranging between 10 and 100 µm. The **influence of the pH** will be studied.

**2- (at ISM-Bordeaux) H**eterogeneous reactivity** between gaseous iodinated species and aqueous aerosols and the physico-chemical evolution of **single particles** exposed to iodine species will be carried out using **acoustic levitation** since this single particle technique can be easily coupled with various analytical techniques. The setup consists in a commercial acoustic levitator device which is included within an environmental jacket to control gaseous environment. This levitation cell is coupled routinely with an optical camera and a Raman microspectrometer for in-situ and on-line characterization of chemical composition and size of single particles. Influence of the particle size, the effect of humidity, the UV-visible irradiation on the chemical (photo)evolution of the particles during gaseous iodinated species exposure and the role of the interface will be investigated. All experiments will be carried out under carefully controlled experimental conditions (temperature, relative humidity, UV radiation intensity, initial reactant mixing ratios).

**Prise de fonction**:

- 02/10/2023**Nature du financement**:

- Contrat doctoral**Précisions sur le financement**:
**Présentation établissement et labo d'accueil**:

- Institut de Radioprotection et de Sûreté NucléaireIRSN, a public expert with industrial and commercial activities, was set up in 2001.The Institute is supervised jointly by the French Minister of the Ecological transition, the French Minister of Defense, and the French Ministers of Energy transition, Research and Health.It is the nation’