At the end of this page, you can find the list of highlights and the full list of publications.
Iodic acid (IA) has recently been recognized as a key driver for new particle formation (NPF) in marine atmospheres. However, the knowledge of which atmospheric vapors can enhance IA-induced NPF remains limited. The unique halogen bond (XB)-forming capacity of IA makes it difficult to evaluate the enhancing potential (EP) of target compounds on IAinduced NPF based on widely studied sulfuric acid systems. Herein, we employed athree-step procedure to evaluate the EP of potential atmospheric nucleation precursors on IA-induced NPF. First, we evaluated the EP of 63 precursors by simulating the formation free energies (ΔG) of the IA-containing dimer clusters. Among all dimer clusters, 44 contained XBs, demonstrating that XBs are frequently formed. Based on the calculated ΔG values, aquantitative structure−activity relationship model was developed for evaluating the EP of other precursors.
F. Ma, H.-B. Xie*, R. Zhang, …, M. Engsvang, J. Elm, X.-C. He*
Environmental Science and Technology (2023)
Iodine is a reactive trace element in atmospheric chemistry that destroys ozone and nucleates particles. Iodine emissions have tripled since 1950 and are projected to keep increasing with rising O3 surface concentrations. Although iodic acid (HIO3) is widespread and forms particles more efficiently than sulfuric acid, its gas-phase formation mechanism remains unresolved. Here, in CLOUD atmospheric simulation chamber experiments that generate iodine radicals at atmospherically relevant rates, we show that iodooxy hypoiodite, IOIO, is efficiently converted into HIO3 via reactions (R1) IOIO + O3 → IOIO4 and (R2) IOIO4 + H2O → HIO3 + HOI + (1)O2. The laboratory-derived reaction rate coefficients are corroborated by theory and shown to explain field observations of daytime HIO3 in the remote lower free troposphere. The mechanism provides a missing link between iodine sources and particle formation. Because particulate iodate is readily reduced, recycling iodine back into the gas phase, our results suggest a catalytic role of iodine in aerosol formation.
H. Finkenzeller+*, S. Iyer+, X.-C. He, …, T. Kurten, M.P. Rissanen, R. Volkamer*
The precise role of HIO2 in iodine oxoacid nucleation remains unclear. In this study, we probe such a role by investigating the cluster formation mechanisms and kinetics of (HIO3)m(HIO2)n (m = 0–4, n = 0–4) clusters with quantum chemical calculations and atmospheric cluster dynamics modeling. The fastest nucleation rate is predicted for mixed HIO3–HIO2 clusters rather than for pure HIO3 or HIO2 ones. Our calculations reveal that the strong binding results from HIO2 exhibiting a base behavior (accepting a proton from HIO3) and forming stronger halogen bonds. Our predicted cluster formation rates and dimer concentrations are acceptably consistent with those measured by the Cosmic Leaving Outdoor Droplets (CLOUD) experiment. This study suggests that HIO2 could facilitate the nucleation of other acids beyond HIO3 in regions where base vapors such as ammonia or amines are scarce.
R. Zhang, H.-B. Xie*, F. Ma., …, M. Sipila, M. Kulmala, X.-C. He*
Environmental Science and Technology 56, 19 (2022)
Iodine species are one of only a handful of atmospheric vapors known to make new aerosol particles, which play a central role in controlling the radiative forcing of climate. He et al. report experimental evidence from the CERN Cosmics Leaving Outdoor Droplets, or CLOUD, chamber demonstrating that iodic acid and iodous acid rapidly form new particles and can compete with sulfuric acid in pristine regions.
X.-C. He*, Y.J. Tham, L. Dada, …, J. Kirkby*, D.R. Worsnop, M. Sipila*
See also Interview with Jasper
Ions enhance the formation rate of atmospheric aerosol particles, which play an important role in Earth’s radiative balance. Although theoretical frameworks exist to calculate the collision rate coefficients between neutral molecules and ions, they need to be experimentally confirmed, ideally under atmospherically relevant conditions of around 1000 ion pairs cm-3$. Here, in experiments performed under atmospheric conditions in the CERN CLOUD chamber, we have measured the collision rate coefficients between neutral iodic acid (HIO3) monomers and charged iodic acid molecular clusters containing up to 11 iodine atoms. Three methods were analytically derived to calculate ion-polar molecule collision rate coefficients.
X.-C. He*, S. Iyer, M. Sipila, …, J. Kirkby*, T. Kurten, M. Kulmala
Aerosol Science and Technology 55, 2 (2021)
Iodine species are important in the marine atmosphere for oxidation and new-particle formation. Here, we describe the application of a bromide chemical ionization mass spectrometer (Br-CIMS) to measure iodine species. We have measured gas-phase iodine species and sulfuric acid using two BrCIMS. From offline calibrations and intercomparisons with other instruments, we have quantified the sensitivities of the Br-MIONCIMS to HOI, I2, and H2SO4 and obtained detection limits of 5.8 × 106, 3.8 × 105, and 2.0 × 105 molec. cm−3, respectively, for a 2 min integration time.
M. Wang+, X.-C. He+*, H. Finkenzeller, …, Y.J. Tham*, N.M. Donahue, M. Sipila
Atmospheric Measurement Techniques 14, 6 (2021)
The postulation that heterogeneous cycling of reactive iodine on aerosols may significantly influence the lifetime of ozone in the troposphere not only remains poorly understood but also heretofore has never been observed or quantified in the field. Here, we report direct ambient observations of hypoiodous acid (HOI) and heterogeneous recycling of interhalogen product species (i.e., iodine monochloride [ICl] and iodine monobromide [IBr]) in a midlatitude coastal environment. Significant levels of ICl and IBr with mean daily maxima of 4.3 and 3.0 parts per trillion by volume (1-min average), respectively, have been observed throughout the campaign. We show that the heterogeneous reaction of HOI on marine aerosol and subsequent production of iodine interhalogens are much faster than previously thought.
Y.J. Tham, X.-C. He, Q. Li, …, M. Dal Maso, A. Saiz-Lopez*, M. Sipila*
Proceedings of the National Academy of Sciences 118, 4 (2021)
Equal contribution (+) and corresponding author (*)
Enhancement of Atmospheric Nucleation Precursors on Iodic Acid-Induced Nucleation: Predictive Model and Mechanism
F. Ma, H.-B. Xie*, R. Zhang, …, M. Engsvang, J. Elm, X.-C. He*
Environmental Science and Technology (2023)
The gas-phase formation mechanism of iodic acid as an atmospheric aerosol source
H. Finkenzeller+*, S. Iyer+, X.-C. He, …, T. Kurten, M.P. Rissanen, R. Volkamer*
Nature Chemistry (2022)
Critical Role of Iodous Acid in Neutral Iodine Oxoacid Nucleation
R. Zhang, H.-B. Xie*, F. Ma., …, M. Sipila, M. Kulmala, X.-C. He*
Environmental Science and Technology 56, 19 (2022)
Role of iodine oxoacids in atmospheric aerosol nucleation
X.-C. He*, Y.J. Tham, L. Dada, …, J. Kirkby*, D.R. Worsnop, M. Sipila*
Science 371, 6529 (2021)
Determination of the collision rate coefficient between charged iodic acid clusters and iodic acid using the appearance time method
X.-C. He*, S. Iyer, M. Sipila, …, J. Kirkby*, T. Kurten, M. Kulmala
Aerosol Science and Technology 55, 2 (2021)
Measurement of iodine species and sulfuric acid using bromide chemical ionization mass spectrometers
M. Wang+, X.-C. He+*, H. Finkenzeller, …, Y.J. Tham*, N.M. Donahue, M. Sipila
Atmospheric Measurement Techniques 14, 6 (2021)
Direct field evidence of autocatalytic iodine release from atmospheric aerosol
Y.J. Tham, X.-C. He, Q. Li, …, M. Dal Maso, A. Saiz-Lopez*, M. Sipila*
Proceedings of the National Academy of Sciences 118, 4 (2021)