Heterogeneous Uptake onto Deliquesced Particles as an Atmospheric Fate of Isoprene-Derived Hydroxy-RO₂

We integrated a chemical conversion technique to transform RO2 into OH radicals with a method combining laser photolysis radical generation and time-resolved OH radical detection by laser-induced fluorescence (LP-LIF). This approach allowed us to investigate the uptake coefficient of an isoprene-derived hydroxy–RO2, ISOPOO (HOC5H8OO·), onto deliquesced NaCl particles and the effect of transition metal ions (Fe2+ and Cu2+) on this uptake. We measured the uptake coefficients, γ, of ISOPOO on deliquesced NaCl particles doped with FeCl2 and CuCl2, each added at 5 wt % of NaCl, at 301 K and 84% relative humidity (RH). The results were 0.45 ± 0.01 for FeCl2 and 0.19 ± 0.01 for CuCl2. These values were 5 and 2 times greater than the uptake coefficient for deliquesced undoped NaCl particles, which was 0.09 ± 0.01. Preliminary simulation results for the western Japan domain, using a value of γ = 0.09 from a three-dimensional chemical transport model, indicate that the heterogeneous uptake of ISOPOO onto deliquesced particles contributed, on average, less than 3% of the ISOPOO loss process. This contribution increased to as much as 5% in remote forest and mountain areas during high PM2.5 events.