Exploring the inorganic composition of the Asian Tropopause Aerosol Layer using medium-duration balloon flights

Abstract

Abstract. Satellite observations have revealed an enhanced aerosol layer near the tropopause over Asia during the summer monsoon, called the “Asian Tropopause Aerosol Layer” (ATAL). In this work, aerosol particles in the ATAL were collected with a balloon-borne impactor near the tropopause region over India, using extended-duration balloon flights, in summer 2017 and winter 2018. The chemical composition of these particles was further investigated by quantitative analysis using offline ion chromatography. Nitrate (NO3-) and nitrite (NO2-) were found to be the dominant ions in the collected aerosols with values ranging between 87 and 343 ng m−3 at STP (standard temperature and pressure) during the summer campaign. In contrast, sulfate (SO42-) levels were found to be above the detection limit (>10 ng m−3 at STP) only in winter. In addition, we determined the origin of the air masses sampled during the flights using the analysis of back trajectories as well as a convective proxy from cloud-top temperature fields derived from a geostationary satellite. The results obtained from this analysis were put into the context of large-scale transport and aerosol distribution using GEOS-Chem chemical transport model simulations. The first flight in summer 2017 which sampled an air mass within the Asian monsoon anticyclone (AMA), influenced by convection over Western China, was associated with particle size diameters from 0.05 to 0.15 µm. In contrast, the second flight sampled air masses at the edge of the AMA associated with a larger particle size radius (>2 µm) with a higher NO2- concentration. The sampled air masses in winter 2018 were likely affected by smoke from the Pacific Northwest fire event in Canada, which occurred 7 months before our campaign, associated with concentration enhancements of SO42- and Ca2+. Overall, our results suggest that nitrogen-containing particles represent a large fraction of cloud-free and in-cloud aerosols populating the ATAL, which is partially in agreement with the results from aircraft measurements during the StratoClim (Stratospheric and upper tropospheric processes for better climate predictions) campaign. The exact nature of those particles is still unknown, but their coincidences with subvisible cirrus clouds and their sizes suggest nitric acid trihydrate (NAT) as a possible candidate, as NAT has already been observed in the tropical upper troposphere and lower stratosphere in other studies. Furthermore, GEOS-Chem model simulations indicate that lightning NOx emissions could have significantly impacted the production of nitrate aerosols sampled during the summer of 2017.

Characterization of refractory aerosol particles collected in the tropical UTLS within the Asian Tropopause Aerosol Layer (ATAL)

“…As a consequence, the chemical composition of aerosol particles in the ATAL may differ from the ground conditions (Froyd et al, 2009;Jost et al, 2017). However, experimental data on physicochemical properties of refractory particles within the ATAL and their sources is sparse (Vernier et al, 2022). This contribution aims on improving the experimental data base in order to gain a better understanding of particle transport into the ATAL.…”

The first balloon-borne sample analysis of atmospheric carbonaceous components reveals new insights into formation processes

“…Together with sulphates and organics, the presence of nitrates, ammonium and mineral dust has been reported in the UTLS above the polluted Asian region during summer monsoon by model simulations [26,27] with possible subsequent influence on the northern hemisphere aerosol content [28]. However, recent aircraft and balloon chemical composition measurements indicate the dominance of secondary aerosols such as nitrate, organics and sulfate with a degree of oxidation increasing with altitudes [29,30]. It remains uncertain if these particles are in an internal or external mixture with the sulfuric acid droplets though [19] suggest rather internal mixtures of sulfate and carbonaceous material.…”

Reconsidering the Existence of a Trend in the Asian Tropopause Aerosol Layer (ATAL) From 1979 to 2017

“…(2019)) and in situ measurements (Appel et al., 2022; Brunamonti et al., 2018; Höpfner et al., 2019; Mahnke et al., 2021; J.‐P. Vernier et al., 2018; H. Vernier et al., 2022). Multiple model studies have investigated the composition, source regions and evolution of the ATAL (e.g., Fadnavis et al.…”

“…The ATAL was first reported by J.-P. Vernier, Thomason, and Kar (2011) with satellite-based data (i.e., CALIOP: Cloud-Aerosol Lidar with Orthogonal Polarization). Since then, the existence of the ATAL was detected with multiple other satellite instruments (Stratospheric Aerosol and Gas Experiment, SAGE II: J.-P. Vernier et al (2015) and Thomason and Vernier (2013), SAGE III/ISS and Ozone Mapping and Profiler Suite, OMPS: Kloss et al (2019); CRyogenic Infrared Spectrometers and Telescopes for the Atmosphere, CRISTA: Höpfner et al (2019)) and in situ measurements (Appel et al, 2022;Brunamonti et al, 2018;Höpfner et al, 2019;Mahnke et al, 2021;J.-P. Vernier et al, 2018;H. Vernier et al, 2022).…”