Atmospheric New Particle Formation

The cast of molecular characters driving NPF

Prototypical NPF is driven by acids (primarily sulfuric acid) and bases (ammonia, amines) because of their ability to transfer protons and form strongly ionically-bound clusters that are less likely to evaporate back to vapors.  Organic acids, produced by oxidation of volatile organic compounds (VOCs), are likely to play a role in NPF, though the exact nature of this role is still unclear.  In polar and coastal regions, iodine-containing compounds such as iodic acid and iodine oxide are important.

Photochemical mechanisms in polar and coastal regions

Iodine oxide particles are likely to form and grow into climatically-relevant aerosol in coastal and polar regions.  While photochemical processing of iodine-containing molecules is relatively well-established, the role of photochemistry in newly-formed particles containing iodic acid and iodine oxides is only beginning to be explored.  We are recording the first UV photolysis spectra of iodine oxide/iodic acid clusters, finding that photolysis rates are high enough that photochemical processes occur in every new particle during formation events.  We observe multiple photolysis products, most importantly atomic oxygen, I2O4, and I2O5, with absorption in the atmospherically-relevant region >300 nm increasing with increasing cluster size.  We hypothesize that this photochemistry may go on to drive interesting intraparticle chemistry that will significantly influence the growth of these new particles.