The upper troposphere and lower stratosphere (UTLS) accommodate a complex mixture of aerosol species. Primary particles emitted from the surface, such as biomass burning, sea salt, and mineral dust, mix with ubiquitous secondary particles composed of sulfate and organic material. In situ mass spectrometry techniques probe these different particle types and their chemical components from airborne platforms with fast time response and very high sensitivity.
In this talk I will describe recent measurements in both the remote and continentally-influenced UTLS and give an overview of several topics where aerosol composition is a key parameter. Composition is a defining property for the ability of aerosol particles to seed ice clouds. Field studies confirm that mineral dust aerosol can dominate cirrus formation in some regions. Recent global sampling campaigns and new quantitative methods yield the first abundance measurements of dust in the background atmosphere, enabling new insights into the prominence of dust to act as a cirrus cloud seed throughout the troposphere. Other climate-relevant aerosol such as biomass burning particles and sea salt are similarly constrained by measurements that are then used to improve emission sources, vertical transport, and radiative effects in global aerosol models. Continental convection provides a sporadic but considerable source of aerosol and precursors to the UTLS. Recent and future high altitude sampling campaigns investigate the impact of continental convection over a wide range of convective environments. Objectives include quantifying the perturbation to background UTLS aerosol abundance and composition, composition-dependent removal, chemical modification of aerosol by cloud processing, source attribution, and quantifying aerosol organic and halogen content.