Large-scale distribution of hydrogen peroxide from aircraft measurements during the TROPOZ II experiment

Aircraft measurements of hydrogen peroxide (H₂O₂) were performed during the TROPOZ II meridional campaign. A specially designed automatic H₂O₂ analyser on board the airplane allowed us to obtain more than 43,000 H₂O₂ measurements. The data set covers a latitude range from 60°N to 60°S and altitudes up to 11 km. Concentration of H₂O₂ ranged from 0.42 ppb (percentile 5) to 6.31 ppb (percentile 95) and exhibited a variability factor of as much as 15. Hydrogen peroxide concentration was typically low (<2 ppb) in the boundary layer of both hemispheres except for the inter-tropical belt, even in America, as well as Africa where the mean mixing ratio reached 5 ppb. In the northern uppermost troposphere a significant increase in H₂O₂ (>3 ppb) could be noticed. Some episodes of high hydrogen peroxide mixing ratio were encountered in the vicinity of cloud systems probably by exchange of H₂O₂ from the liquid phase to the gas phase.