Raman Microspectroscopic Analysis of Size-Resolved Atmospheric Aerosol Particle Samples Collected with an ELPI: Soot, Humic-Like Substances, and Inorganic Compounds

Abstract

Raman microspectroscopy and mapping have been applied for the analysis of soot, humic-like substances (HULIS) and inorganic compounds in size resolved samples of air particulate matter collected with an electrical low pressure impactor (ELPI). Using several reference materials, we found that spectral parameters determined by curve fitting with five bands (G, D1-D4) enable a discrimination of soot and HULIS and provide information about the relative abundance and structural order of graphite-like carbon. In particular, the D1 band width exhibited a near-linear negative correlation with the ratio of apparent elemental carbon to total carbon in different types of soot.The ELPI samples of sub-micrometer atmospheric particles exhibited essentially the same Raman spectra and parameters as standard diesel soot. In winter samples this was also the case for larger particles with aerodynamic diameters up to 4 μm. Spring and autumn samples, however, exhibited increased D1 band widths and D3 band intensities, indicating a high prevalence of HULIS in the size range of 2-4 μm. In addition, various nitrates and sulfates (mostly NaNO 3 and (NH 4 ) 2 SO 4 ; some NH 4 NO 3 , Ca(NO 3 ) 2 , Na 2 SO 4 , and CaSO 4 ) and small amounts of CaCO 3 were detected. Different single-and multi-component spectra indicated the presence of externally and internally mixed particles. The relative abundance of different chemical components in different particle size ranges was quantified in mapping experiments (0-55% NaNO 3 , 1-15% (NH 4 ) 2 SO 4 , 10-45% soot/HULIS, 30-60% highly fluorescent organics). Overall, the results of this study demonstrate that Raman microspectroscopy and mapping can provide qualitative and quantitative information about the composition of ELPI aerosol samples.

Chemical characterization of laboratory-generated tar ball particles

“…The O / C molar ratio of other atmospheric TBs varies widely and in some cases compares better with the O / C molar ratio of HULIS. As expected from the above results, the mean carbon to mass conversion factor of our Lab-TBs (1.21; RSD: 0.5 %) is between that of HULIS (1.81-1.93; Krivácsy et al, 2001;Kiss et al, 2002;Salma et al, 2007) and soot samples (1.04-1.15; Akhter et al, 1985;Clague et al, 1999).…”

“…However, when comparing the elemental compositions of our Lab-TBs to that of HULIS, both the O / C (0.094-0.109) and the H / C (0.511-0.584) molar ratios of our Lab-TBs were substantially lower than those reported for HULIS samples (O / C: 0.455-0.563; H / C: 1.431-1.537) (Krivácsy et al, 2001;Kiss et al, 2002;Salma et al, 2007). The O / C molar ratio of other atmospheric TBs varies widely and in some cases compares better with the O / C molar ratio of HULIS.…”

Characterization of Exhaust Particulates from a Dual Fuel Engine by TGA, XPS, and Raman Techniques

“…In the present study this intensity ratio varied from 0.5 for diesel (light) to 1.3 for dual fuel PM samples (Table 5) indicating the more amorphous nature of the carbon in dual fuel PM compared to diesel (high) samples. Ivleva et al (2007) correlated the intensity ratio, I D3 /I G , to the ratio of elemental carbon (EC) to total carbon (TC) present in PM. According to the authors the decrease in the intensity ratio with increasing EC/TC ratio implied a decrease in amorphous organic carbon fraction.…”

Heterogeneous Uptake of Amines by Citric Acid and Humic Acid

“…31 On the other hand, humic-like substances (HULIS) were also found as a major part of the OA in urban fine PM. 32,33 In this study, we investigated the heterogeneous uptake of MA, DMA, and TMA on citric acid and humic acid as representatives of carboxylic acids present in atmospheric PM. γ were measured at 298 K using a Knudsen cell reactor coupled to a quadrupole mass spectrometer (QMS).…”