Characterizing the Asian Tropopause Aerosol Layer Using Satellite Observations, in Situ Balloon Measurements, and Chemical Transport Modeling

Satellite observations and numerical modeling studies have demonstrated that the Asian Summer Monsoon (ASM) can provide a conduit for gas-phase pollutants in south Asia to reach the lower stratosphere. Observations from the CALIPSO satellite have revealed the Asian Tropopause Aerosol Layer (ATAL), a summertime accumulation of aerosols in the upper troposphere and lower stratosphere (UTLS), associated with ASM anticyclone. The ATAL has potential implications for regional cloud properties, climate, and chemical processes in the UTLS. Here, we illustrate the development and long-term trend of the ATAL based on CALIPSO and SAGE II measurements. We

show in situ measurements from balloon-borne instruments, aircraft and satellite observations, combined with trajectory and chemical transport model (CTM) simulations to explore the origin, composition, physical and optical properties of aerosols in the ATAL. We show balloon-based observations from our BATAL-2015 field campaign to India and Saudi Arabia in summer 2015, including in situ measurements from COBALD back scatter sondes, and some of the first observations of size and volatility of aerosols in the ATAL layer using optical particle counters (OPCs). Back trajectory calculations initialized from CALIPSO observations point to deep convection over North India as a principal source of ATAL aerosols. Available aircraft observations suggest significant carbonaceous contributions to the ATAL, which is supported by simulations using the GEOS-Chem CTM. Source elimination studies conducted with the GEOS-Chem indicate that 70-80% of ATAL aerosols originate from South Asian sources, in contrast with some earlier studies.