Spectro-Microscopy Studies of Atmospheric Particles

Principal Investigator(s):
Alexander Laskin, Purdue University

This project will provide physico-chemical description of individual atmospheric particles collected during field studies at DOE ARM sites. We will focus our efforts on systematic spectro-microscopy studies of particles collected during the ACE-ENA experiment (2017-2018) with secondary efforts devoted to particles from the HI-SCALE (2016-2017) and GOAmazon (2014/2015) experiments. Our goals are to 1) investigate the contribution of natural and anthropogenic sources to populations of atmospheric particles during representative atmospheric conditions for each site 2) characterize their hygroscopic properties and propensities to CCN and IN activity, 3) evaluate optical properties of typical particle ensembles in the areas of studies with respect to their composition and mixing state.

Using spectromicroscopy techniques, we will examine elemental and molecular composition, mixing state, size, and higher order morphology for individual particles. By combining these analyses with concurrent trace gases, meteorological, cloud, and in-situ aerosol measurements, we will contribute to the ACE-ENA study by addressing the following scientific questions: (1) What are the aerosol properties, including size distribution, composition, mixing state, morphology, and hygroscopicity of particles in the mid-Atlantic marine boundary layer (MBL) and free troposphere (FT)? (2) What are the contributions of different aerosol sources (i.e., local natural versus long-range transported anthropogenic sources) to the MBL and FT cloud nuclei budgets? (3) How do aerosol properties and the contributions from different sources/pathways vary with air mass type, meteorological and cloud conditions, and marine biological activities? Similarly, our objectives for the analysis of particles collected in other two studies include, but are not limited to: (1) Characterization of external and internal mixing of particles to document their atmospheric sources and transformations during different meteorological conditions; (2) Determine differences in chemical composition and physical state (phase and volatility) of particles; (3) Assessment of particle hygroscopic, CCN, IN and optical properties.

Comprehensive offline analyses of particle samples will be carried out to characterize particle composition, mixing state, size, and morphology. Elemental composition will be quantified using computer controlled scanning electron microscopy and X-ray microanalysis. Transmission electron microscopy will provide higher resolution measurements for particles smaller than ~200 nm. The chemical bonding speciation of carbon, nitrogen, oxygen and sulfur in the individual particles will be probed using scanning transmission X-ray microscopy. Combined together, results of these analyses will allow an assessment of the major particle sources (biogenic vs. anthropogenic, primary vs secondary), and will provide key information on the evolution processes of aerosol particles such condensation, coagulation, aging, and cloud processing in the atmosphere.

The particle composition, mixing state, and morphology from analyzed periods will be combined with in-situ measurements of aerosol size distribution, CCN concentration, hygroscopicity, and aerosol bulk composition. Particles in selected samples will be microscopically probed to investigate their optical and hygroscopic properties, liquid-liquid and solid-liquid phase separations, and ice nucleation activity. In combination, these data sets will allow for a detailed examination of how sources and mixing state impact cloud formation and radiative balance for these unique regions of the Earth. In collaboration with other scientists involved in the ACE-ENA, HI-SCALE and GOAmazon field campaigns, we will carry out statistical analysis of particle properties and their source-specific contributions to regional aerosol loading under representative air mass, meteorological, and cloud conditions.