To explain the elevated levels of HO X in the upper troposphere, a number of new sources have been proposed. These cases were often associated with recent deep convection. Thus, injection of air from the surface, carrying high levels of HO X precursors, could be an additional HOx source to the upper troposphere. However, it was not possible to test the importance of these new sources directly because they were not measured during the initial three campaigns. These observations allowed a detailed evaluation of our understanding of HOx chemistry in the upper troposphere.
Observations are for cloud-free, daytime conditions.
Adapted from Brune et al . The observations shown in Figure 1 are for cloud-free, daytime conditions only. Although the concentrations of these HO X precursors were enhanced in fresh convective outflows, the enhancements were driven primarily by the high levels of water vapor in these outflows. 2 NO 2 and NO 2 . This results in the well known non-linear dependence of HO X and ozone production on NO X , which we can now test directly in the atmosphere with measurements of HO X and NO X species.