Mid‐tropospheric aerosol backscatter background mode over the Pacific Ocean at 9.1 µm wavelength

The first atmospheric aerosol backscatter measurements at the rare isotope CO2 wavelength of 9.1 µm were obtained in the troposphere over the Pacific Ocean in May–June 1990. A distinct aerosol backscatter background mode was found in both hemispheres with modal value ∼10−10 m²kg−1sr−1 (backscatter normalized by air density), remarkably consistent with ground‐based and airborne backscatter climatologies collected at other wavelengths, locations, and times.