Influence of southern hemispheric biomass burning on midtropospheric distributions of nonmethane hydrocarbons and selected halocarbons over the remote South Pacific.

Aircraft measurements of nonmethane hydrocarbons (NMHCs) and halocarbons were made over the remote South Pacific Ocean during late August‐early October 1996 for NASA's Global Tropospheric Experiment (GTE) Pacific Exploratory Mission‐Tropics A (PEM‐Tropics A). This paper discusses the large‐scale spatial distributions of selected trace gases encountered during PEM‐Tropics A. The PEM‐Tropics A observations are compared to measurements made over the southwestern pacific in early November 1995 as part of Aerosol Characterization Experiment (ACE 1). Continental pollution in the form of layers containing elevated levels of O 3 was observed during a majority of PEM‐Tropics flights, as well as during several ACE 1 flights. The chemical composition of these air masses indicates that they were not fresh and were derived from nonurban combustion sources. The substantial impact of biomass burning on the vertical structure of the South Pacific troposphere is discussed.