Cathy Banic

Airborne measurements of aqueous and gaseous hydrogen peroxide during spring and summer in Ontario, Canada

Measurements of H 2 O 2 , both in the gas phase and in cloudwater samples, were made over central Ontario during the summer 1988 and spring 1990 intensive measuring periods of the Eulerian Model Evaluation Field Study from a Twin Otter aircraft. Cloudwater concentrations range from less than 1.5 μM to greater than 100 μM; corresponding gaseous concentrations range from less than 0.1 parts per billion by volume (ppbv) to approximately 2.5 ppbv. Gas phase H 2 O 2 data are corrected for instrument response and the interphase partitioning of H 2 O 2 is examined. Ratios of the measured to predicted partitioning based on Henrys law equilibrium range from approximately 0.2 to 1. When the data correction is applied, most samples do not differ from equilibrium by more than 20%. Lower ratios are associated with samples from supercooled clouds or samples taken when interstitial SO 2 is high. The measured aqueous fraction for the supercooled samples is approximately 20% of that expected by Henrys law equilibrium. The ratios are independent of liquid water content but show some dependence on pH