| The reactive iodine radicals including atomic iodine（I·）,iodine monoxide（IO·）,iodine dioxide（OIO）and I2·-radicals have been widely detected in the global atmosphere and may exhibit significant atmospheric impacts such as tropospheric ozone depletion,altering HOx and NOx chemistry,mercury oxidation,formation of cloud condensation nuclei and aerosol,and further influencing climate.Of these reactive iodine radicals,I·/I2·-radicals are considered as the initial radicals playing crucial roles for the generation of other iodine radicals by chain reactions.However,the current understanding on the formation of iodine radicals in atmospheric aqueous aerosol is still quite limited.In this study,employing modern analysis method including laser flash photolysis（LFP）,three-dimensional excitation emission matrix fluorescence（3DEEM）,ultraviolet-visible spectroscopy（UV-Vis）,total organic carbon（TOC）,ion chromatography（IC）,and high-performance liquid chromatography（HPLC）,combined with steady-state photolysis and quenching experiment,we do the research about exploring the main component dissolved photosensitive matters（DPSM）in atmospheric aqueous aerosol,analysis of mechanisms on the I·/I2·-radicals photo-generation pathways,mechanism and kinetics,and the calculation of photochemical generation rate of I·/I2·-radicals via photo-generation pathways in each reaction system.The main results are as follows:1.Dissolved organic matters（DOM）,Fe-complexes[Fe（Ⅲ）],nitrate ions（NO3-）and nitrite ions（NO2-）were the major components of DPSM in atmospheric aqueous aerosol,where the contents of most DPSM in haze were higher than that in non-haze.1.67±1.39μM and 2.63±0.14μM of Fe（Ⅲ）-complexes,224.96±8.14μM and 140.56±6.22μM of NO3-,and 124.48±3.32μM and 78.13±0.13μM of NO2-were found in aqueous extracts of haze and non-haze aerosol samples,respectively.2.I·/I2·-radicals can be produced simultaneously in aqueous aerosol by several sunlight-driven photochemical pathways under simulated sunlight.（1）The I·was produced via direct photo-dissociation of SOI and further reacted with I-to form I2·-.（2）The I·was produced by·OH-mediated oxidation of I-in which·OH radicals were generated due to the photolysis of DPSM（Fe（Ⅲ）-complexes,NO3-,HNO2/NO2-）.（3）And the I·was also the production of triplet excited state of DOM（3DOM*）-induced oxidation of I-,in which DOM was excited by the absorption of a photon to form the excited singlet state of CDOM,1DOM*following the conversion of 1DOM*to 3DOM*via the intersystem crossing.Meanwhile,the pathway of eaq--initiated stepwise reduction of IO3-to I2（aq）and further photolyzed into I·plays negligible role in formation of I·/I2·-radicals due to the low reaction rates and severe quenching effect of eaq-by dissolved O2.3.Second-order reaction rate constant（kI·2-）of I·+I-→I2·-in aqueous Fe（Ⅲ）-FA mixture,NO3-,HNO2/NO2-,and H2O2 spiked with a series of concentrations of I-were 9.0×109 M-1 s-1,1.25×1010 M-1 s-1,5.1×109 M-1 s-1,and 5.5×109 M-1 s-1,respectively.Of these photochemical pathways,the formation rates of I·and I2·-（RI·and RI·2-）were determined as 0.10～1.34×10-9 M ns-1 and 0.99～5.68×10-7 Mμs-1for photolysis of SOI（5.0 mM）mixed with I-（0.2～2.0 mM）,0.03～1.41×10-8 M ns-1 and 0.05～4.10×10-6 Mμs-1 for·OH-mediated oxidation of I-in aqueous DPSM（Fe（Ⅲ）-complexes,NO3-,NO2-）spiked with I-（0.1～1.0m M）,and 1.57～1.65×10-9 M ns-1 and 0.99～5.68×10-7 Mμs-1 for 3DOM*-induced oxidation of I-in aqueous DOM(0.25 mg L-1)spiked with I-（0.5～1.0 mM）,respectively.RI·and RI·2-also increased as the concentration of I-spiked increases.This work comprehensively investigated the mechanisms and kinetics on the photochemical reactions involved in the formation of I·/I2·-radicals in atmospheric aqueous aerosol,and would help to better understand the transformation mechanism of iodine species,pathways of iodine cycling and the associated environmental impacts involving atmospheric reactive iodine radicals. |
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