Aviation and Chemistry and Transport Processes in the Upper Troposphere and Lower Stratosphere

Abstract

Aircraft emissions impact the atmosphere in a variety of ways, including enhancing greenhouse gases, especially water vapor and carbon dioxide, in the upper troposphere and lower stratosphere, forming persistent contrails, and altering the distributions of reactive chemical species, which change the oxidative capacity of the atmosphere. This paper summarizes some recent findings related to the impacts of aircraft exhaust on the chemistry of the upper troposphere and lower stratosphere (UTLS). Of particular note are the improvements in our understanding of production of nitrogen oxides (NOx ~ NO + NO2) by lightning and of the influence of long-range transport on background abundances of reactive species. Studies have also identified gaps in our knowledge, including the behavior of HOx (OH and HO2) species at high NOx and discrepancies in measurements of water vapor in the relatively dry UTLS. Lack of detailed observations of species, such as the halogens chlorine and bromine, limits our ability to assess the role of heterogeneous chemistry on UTLS chemistry with or without the influence of aircraft exhaust. Recommendations for studies that address these issues are presented.