A large organic aerosol source in the free troposphere missing from current models

Aircraft measurements of organic carbon (OC) aerosol by two independent methods over the NW Pacific during the ACE‐Asia campaign reveal unexpectedly high concentrations in the free troposphere (FT). Concentrations average 4 μg sm −3 in the 2–6.5 km column with little vertical gradient. These values are 10–100 times higher than computed with a global chemical transport model (CTM) including a standard 2‐product simulation of secondary organic aerosol (SOA) formation based on empirical fits to smog chamber data. The same CTM reproduces the observed vertical profiles of sulfate and elemental carbon aerosols, which indicate sharp decreases from the boundary layer to the FT due to wet scavenging. Our results…

• NS
  National Science Foundation
• NA
  National Aeronautics and Space Administration