FTIR analysis of surface functionalities on particulate matter produced by off-road diesel engines operating on diesel and biofuel.

Fourier transform infrared spectroscopy is applied as a powerful analytic technique for the evaluation of the chemical composition of combustion aerosols emitted by off-road engines fuelled by diesel and biofuels. Particles produced by burning diesel, heated rapeseed oil (RO), RO with ethylhexylnitrate, and heated palm oil were sampled from exhausts of representative in-use diesel engines. Multicomponent composition of diesel and biofuel particles reveal the chemistry related to a variety of functional groups containing carbon, hydrogen, oxygen, sulfur, and nitrogen. The most intensive functionalities of diesel particles are saturated C-C-H and unsaturated C=C-H aliphatic groups in alkanes and alkenes, aromatic C=C and C=C-H groups in polyaromatics, as well as sulfates and nitrated ions. The distinguished features of biofuel particles were carbonyl C=O groups in carboxylic acids, ketones, aldehydes, esters, and lactones. NO2, C-N and -NH groups in nitrocompounds and amines are found to dominate biofuel particles. Group identification is confirmed by complementary measurements of organic carbon (OC), elemental carbon, and water-soluble ion species. The relationship between infrared bands of polar oxygenated and non-polar aliphatic functionalities indicates the higher extent of the surface oxidation of biofuel particles. Findings provide functional markers of organic surface structure of off-road diesel emission, allowing for a better evaluation of relation between engine, fuel, operation condition, and particle composition, thus improving the quantification of environmental impacts of alternative energy source emissions.

Cloud condensation nuclei and ice nucleation activity of hydrophobic and hydrophilic soot particles.

Cloud condensation nuclei (CCN) activity and ice nucleation behavior (for temperatures

Water interaction with hydrophobic and hydrophilic soot particles.

The interaction of water with laboratory soots possessing a range of properties relevant for atmospheric studies is examined by two complementary methods: gravimetrical measurement of water uptake coupled with chemical composition and porosity analysis and HTDMA (humidified tandem differential mobility analyzer) inference of water uptake accompanied by separate TEM (transmission electron microscopy) analysis of single particles. The first method clarifies the mechanism of water uptake for bulk soot and allows the classification of soot with respect to its hygroscopicity. The second method highlights the dependence of the soot aerosol growth factor on relative humidity (RH) for quasi-monodisperse particles. Hydrophobic and hydrophilic soot are qualitatively defined by their water uptake and surface polarity: laboratory soot particles are thus classified from very hydrophobic to very hydrophilic. Thermal soot particles produced from natural gas combustion are classified as hydrophobic with a surface of low polarity since water is found to cover only half of the surface. Graphitized thermal soot particles are proposed for comparison as extremely hydrophobic and of very low surface polarity. Soot particles produced from laboratory flame of TC1 aviation kerosene are less hydrophobic, with their entire surface being available for statistical monolayer water coverage at RH approximately 10%. Porosity measurements suggest that, initially, much of this surface water resides within micropores. Consequently, the growth factor increase of these particles to 1.07 at RH > 80% is attributed to irreversible swelling that accompanies water uptake. Hysteresis of adsorption/desorption cycles strongly supports this conclusion. In contrast, aircraft engine soot, produced from burning TC1 kerosene in a gas turbine engine combustor, has an extremely hydrophilic surface of high polarity. Due to the presence of water soluble organic and inorganic material it can be covered by many water layers even below water saturation conditions. This soot demonstrates a gradual diameter growth factor (D(wet)/D(dry)) increase up to 1.22 at 93% relative humidity, most likely due to the presence of single particles with water soluble material heterogeneously distributed over their surface.