Halogenated species have a significant impact on atmospheric composition, including catalytic ozone destruction and influence on HOx and NOx cycles. Halogens are also involved in marine and coastal new particle formation, a process that can ultimately affect Earth's radiation balance. However, the exact processes governing halogen chemistry and halogen new particle formation have been puzzling the community for years.
One of the major difficulties in understanding these processes has been the lack of techniques able to measure inorganic halogenated radicals and stable species simultaneously both in laboratory studies and in ambient conditions. This is because previous spectroscopic and mass spectrometric methods utilized could only measure one, or a few halogenated species at once, while most of the halogenated species existing in the atmosphere were likely un-measurable. Here we present new chemical ionization (CI) mass spectrometric methods to measure over 20 halogenated species simultaneously at ambient pressure. These species include halogen oxides, halogen acids, nitrogen containing halogen species, halogen radicals and molecular halogens, covering the major categories present in the ambient atmosphere. The methods will further be deployed into field measurements in various locations around the world to better understand the impact of halogenated species to the atmosphere.
A recent study revealed homogeneous nucleation processes by (HIO3) (brackets here indicate all the isomers). However, the exact formation mechanism of (HIO3) has not been investigated in laboratory experiments. We deployed the above mentioned new measurements methods to study the formation mechanism of (HIO3) in dedicated flow tube experiments. The results show that OIO and OH radical could form (HIO3) as indicated by previous quantum mechanism calculations. In addition, two novel (HIO3) formation pathways from photo-oxidation of CH2I2 and molecular iodine were suggested. One pathway shows that the homogeneous bimolecular reaction of CH2IOO could form (HIO3), while the other suggests either iodine radical or iodine monoxide could react with ozone and water vapor to form (HIO3). These findings could potentially explain the large amount of (HIO3) observed.
Beside from coastal areas, the first ambient data showing the existence of (HIO3) in various locations in the world, including a boreal forest site, a wet land site, Greenland and Antarctica are also presented here. These findings indicate that the (HIO3) might be involved in nucleation processes in locations other than coastal areas.
More than (HIO3), sulfuric acid is known for its active role in atmospheric nucleation over different environments. However, the knowledge of its gas phase oxidation processes is not complete. Our laboratory results imply that iodinated species might be able to oxidize SO2 to sulfuric acid through some yet unknown mechanisms. Further studies are needed to understand the exact mechanisms in the oxidation processes and how important this mechanism could be in the ambient atmosphere.
