Soot particles emitted by aircraft engines may act as ice nuclei (IN) within the atmosphere, subsequently triggering the formation of condensation trails. Such contrails might further evolve as cirrus clouds, and thus greatly influence the Earth's radiative budget and impact the amount of precipitation. In order to monitor in-situ deliquescence, efflorescence, and nucleation processes followed by ice growth in the laboratory, we developed the Ice and Droplet Nucleation Experimental Setup (IDroNES), which combines optical imaging and micro-Raman measurements to follow nucleation events in a pressure-, temperature-and humidity-controlled optical chamber. We first compare against literature data, and later confirm, the deliquescence relative humidities of micron-sized sodium chloride salt crystals in the -5°C to -35°C temperature range. Then, we investigate the ice nucleation activity of graphite and aircraft soot analogs, in the -15°C to -45°C temperature range, when exposed to humid nitrogen (N2/H2O gas flow). Soot samples exhibiting various surface chemistries, morphologies, and sizes are thoroughly examined via mass spectrometry, and spectroscopic and optical techniques. All carbon-bearing samples are found active at nucleating ice at low ice saturation ratios (Sice determined when the first crystal is detected). When normalizing Sice to the total surface area of a sample, one can derive the ice-active surface site density (ns). This parameter provides a means to compare the ice nucleating behavior of various particle types with distinct surface areas. As all samples studied in our work feature large surface areas, we provide ice nucleation data (Sice and ns) for a range of surface areas that remained largely unexplored to date. We find that the interplay between surface composition and morphology (micro, meso, and macro pores, surface roughness) influences the ice onset relative humidity.

Abstract. Combustion of hydrocarbons produces both particulate and gas phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose to couple a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate and gas phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through, and then trap the most volatile components on a second black carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling/multi-technique approach in conjunction with advanced statistical methods we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry.

Abstract. Combustion of hydrocarbons produces both particulate- and gas-phase emissions responsible for major impacts on atmospheric chemistry and human health. Ascertaining the impact of these emissions, especially on human health, is not straightforward because of our relatively poor knowledge of how chemical compounds are partitioned between the particle and gas phases. Accordingly, we propose coupling a two-filter sampling method with a multi-technique analytical approach to fully characterize the particulate- and gas-phase compositions of combustion by-products. The two-filter sampling method is designed to retain particulate matter (elemental carbon possibly covered in a surface layer of adsorbed molecules) on a first quartz fiber filter while letting the gas phase pass through and then trap the most volatile components on a second black-carbon-covered filter. All samples thus collected are subsequently subjected to a multi-technique analytical protocol involving two-step laser mass spectrometry (L2MS), secondary ion mass spectrometry (SIMS), and micro-Raman spectroscopy. Using the combination of this two-filter sampling–multi-technique approach in conjunction with advanced statistical methods, we are able to unravel distinct surface chemical compositions of aerosols generated with different set points of a miniCAST burner. Specifically, we successfully discriminate samples by their volatile, semi-volatile, and non-volatile polycyclic aromatic hydrocarbon (PAH) contents and reveal how subtle changes in combustion parameters affect particle surface chemistry.

S1 L2MS spectra Figure S1. Comparison between mass spectra for SP1, SP2, SP3, and SP4 samples recorded with λi = 157 nm and λi = 118 nm for Front Filters (lower spectra) and Back Filters (upper spectra).