The Global Distribution of Sea Salt Aerosol

We present the first measurements of the concentration of sea salt aerosol over a wide range of latitude and altitude in the troposphere. The Particle Analysis by Laser Ionization Mass Spectrometry (PALMS) instrument measured the concentration of a wide variety of aerosol species during the deployments of the Atmospheric Tomography Mission (ATom). In particular, concentrations of sea salt were measured from near the surface to the lower stratosphere. Inferred concentrations near the surface are within the range of previous measurements. The concentration of sea salt falls off very rapidly with altitude, roughly a factor of 10 for every 2 km. This indicates efficient removal by precipitation. What sea salt was present above 4 km was notably chemically aged compared to sea salt in the boundary layer. The measured concentrations of sea salt in the upper troposphere were so small that reactions on sea salt cannot significantly affect the nitrate, sulfate, chorine, or bromine budgets in the upper troposphere. The measured concentrations will be compared to global models, with one model overestimating sea salt aerosol in the upper troposphere by factors of 10 to 1000. Making the removal of sea salt aerosol proportional to the removal of water may be an extremely simple and reasonably accurate parameterization.