Quantitative determination of I2/IO using a dual-channel BBCEAS system and its laboratory validation

Correspondence: Min Qin(mqin@aiofm.ac.cn) , Pinhua Xie (phxie@aiofm.ac.cn)

Iodine (I) in the atmosphere not only provides an important source of iodine for mammals, but also affects the catalytic depletion of ozone in the atmosphere, the production of important free radicals such as OH, and the formation of marine aerosols. Its atmospheric chemical behavior has been an important topic in atmospheric chemistry research in recent years. Research has found that iodine oxide plays an important role in the formation process of ultrafine aerosol particles (particle size between 3-10 nm), especially in the oceanic boundary layer (i.e. iodine oxide particles, IOPs). The chemical composition analysis of new particles in the ocean boundary layer shows that the nucleation and growth of particles are mainly controlled by condensable iodine vapor. The ship measurement results of halogen oxides in the Arctic high boundary layer show that iodine will exacerbate the depletion of tropospheric ozone in spring. The chemical reaction between iodine and ozone is the second largest factor causing ozone loss, second only to the loss caused by ozone photolysis. Currently, most laboratories primarily rely on chemical methods for iodine analysis. However, the high cost of associated instruments makes it difficult to meet routine analytical demands. In the field of optical methods, various spectroscopic techniques have been developed and applied, such as long-path differential optical absorption spectroscopy (DOAS), cavity ring-down spectroscopy (CRDS), and cavity-enhanced absorption spectroscopy (CEAS).This study used Broadband cavity-enhanced absorption spectroscopy (BBCEAS) technology. A homemade dual-cavity BBCEAS system integrated with green and blue LEDs enables in situ simultaneous measurement of I₂ and IO (iodine monoxide). With a time resolution of 60 seconds, The limit of detection (2σ) of the measurement system reached 1.13 pptv for I₂ and 1.31 pptv for IO. It has already been applied in laboratory-based measurement experiments.