Diurnal variations in H₂O₂, O₃, PAN, HNO₃ and aldehyde concentrations and NO/NO₂ ratios at Rishiri Island, Japan: Potential influence from iodine chemistry

The presence of iodine chemistry, hypothesized due to the overprediction of HO₂ levels by a photochemical box model at Rishiri Island in June 2000, was quantitatively tested against the observed NO/NO₂ ratios and the net production rates of ozone. The observed NO/NO₂ ratios were reproduced reasonably well by considering the conversion of NO to NO₂ by IO, whose amount was calculated so as to reproduce the observed HO₂ levels. However, the net production rates of ozone were calculated to be negative when such high mixing ratios of IO were considered, which was inconsistent with the observed buildup of ozone during daytime. These results suggest that iodine chemistry may not be the sole mechanism for the reduced mixing ratios of HO₂, or that "hot spots" for iodine chemistry were present. Diurnal variations in the mixing ratios of HCHO, CH₃CHO, peroxy acetyl nitrate (PAN) and HNO₃ observed during the study are presented along with the simulated ones. The box model simulations suggest that the effect of iodine chemistry on these concentrations is small and that important sources of CH₃CHO and sinks of PAN are probably missing from our current understanding of the tropospheric chemistry mechanism.