Evaluating the importance of nitrate aerosol in the upper troposphere and lower stratosphere during the Asian summer monsoon season

Abstract

The Asian Summer Monsoon (ASM), as well as tropical convection, transport aerosols and their precursors from the boundary layer to the upper troposphere and lower stratosphere (UTLS). We utilize the Community Aerosol and Radiation Model for Atmospheres (CARMA) coupled with the Community Earth System Model (CESM) to simulate all major tropospheric aerosols including sulfate, organics, ammonium, nitrate, sea salt, and dust. We evaluate the model during the ASM season by comparing the simulated aerosol microphysical properties, such as particle compositions, size distribution, and particle volume with MIPAS satellite and in-situ data from three field campaigns. We find nitrate, organics, and sulfate contribute significantly to the UTLS optical properties between 0-45˚N, 0-180˚E. The major source of nitrate is the ammonium nitrate formed locally and nitric acid condensation near the cold tropopause. Including nitrate in the model doubles the surface area density between 0-45˚N, 0-180˚E, which alter the chlorine partitioning at the UTLS region.