Lifetimes and transport characteristics of different-sized aerosols in the Asian Tropopause Aerosol Layer: a climate model study

Abstract. Using the Community Earth System Model (CESM), a series of sensitivity experiments were conducted to investigate the lifetimes and transport characteristic of different-sized aerosol particles within the Asian tropopause aerosol layer (ATAL). The results reveal that during the Asian summer monsoon (ASM) period, small particles, represented by Aitken-mode sea salt (NCl a2, 0.015–0.052 μm in diameter), can reside stably in the upper troposphere–lower stratosphere (UTLS) region and undergo extensive horizontal transport. The mean lifetime of NCl a2 particles reaches up to 552 days, while those of fine (0.095–0.56 μm) and coarse (0.63–3.70 μm) sea salt particles have an average lifetime of approximately 28 days and 11 days, respectively. The trapping effect of the ASM circulation on particles released at various heights within the ATAL (180–80 hPa) can maintain even after 120 days. When aerosol particles are released below the ATAL, the number of particles entering the UTLS region varies significantly with the release sites, i.e., aerosols released over South Asia (an effective upward transport pathway) more readily enter the ASM anticyclone and the stratosphere and reside longer in the UTLS region than particles released at the ASM anticyclone hinterland and the East Asia (EA) site.