Mineralogy and mixing state of North African mineral dust by on-line single-particle mass spectrometry

Abstract

Abstract. The mineralogy and mixing state of dust particles originating from the African continent influences climate and marine ecosystems in the North Atlantic due to its effect on radiation, cloud properties and biogeochemical cycling. Single-particle mineralogy and mixing state is particularly important in many processes but is difficult to predict because of large temporal and spatial variability and the lack of in-situ measurements of dust properties during emission, transport and deposition. This lack of measurements is in part due to the remoteness of potential source areas (PSA) and transport pathways, but also because of 5 the lack of an efficient method to report the mineralogy and mixing state of single particles with a time resolution comparable to atmospheric processes.In this work, the mineralogy and mixing state of the fine fraction (< 2.5µm) in laboratory suspended dust from the Sahara and Sahel were made using novel techniques with on-line single-particle mass spectrometry (SPMS) and traditional off-line scanning electron microscopy (SEM). A regional difference in mineralogy was detected, with material sourced from Morocco 10 contained a high number fraction of illite like particles in contrast to Sahelian material which contains potassium and sodium depleted clay minerals like kaolinite. Applying the same methods to ambient measurement of transported dust in the marine boundary layer at Cabo Verde in the remote North Atlantic enabled the number fractions of illite/smectite clay mineral (ISCM), non-ISCM, and calcium containing particles to be reported at a 1 hour time resolution over a 20 day period alongside internal mixing with nitrate, sulphate and organic/biological material. The ISCM and nitrate content was found to change significantly 15 between distinct dust events, indicating a shift in source and transport pathways which may not be captured in off-line composition analysis or remote sensing techniques.The results show SPMS and SEM techniques are complimentary and demonstrate that SPMS can provide a meaningful high resolution measurement of single-particle mineralogy and mixing state in laboratory and ambient conditions. In most cases, the mineralogy varies continuously between particles rather than a collection of discrete mineral phases. These techniques 20 will be useful in resolving the complexity of mineral dust transport and in obtaining atmospherically relevant test material for laboratory experiments of dust properties.

Computational Study of the Effect of Mineral Dust on Secondary Organic Aerosol Formation by Accretion Reactions of Closed-Shell Organic Compounds

“…However, their relative amounts are significantly lower than those of feldspars and quartz. 67 It should be also noted that molten clays can transform into feldspars as they mostly consist of phyllosilicates 60 . Our model dust minerals were thus assumed to contain only feldspars and quartz.…”

“…67 It should be also noted that molten clays can transform into feldspars as they mostly consist of phyllosilicates. 60 Our model dust minerals were thus assumed to contain only feldspars and quartz. Since…”

“…57 Also, their chemical and physical properties change upon aging 58,59 and phase transitions. 58 Moreover, the distribution of mineral components in dust is naturally inhomogeneous 60 and mineral components may have different particle sizes. 60,61 To simplify the problem, we focused on the major dust minerals.…”

“…58 Moreover, the distribution of mineral components in dust is naturally inhomogeneous 60 and mineral components may have different particle sizes. 60,61 To simplify the problem, we focused on the major dust minerals. Based on numerous studies on dust components, quartz is the major oxide component of mineral dust (40− 70%).…”

Understanding of atmospheric aerosol particles with improved particle identification and quantification by single particle mass spectrometry

“…A combination of peak area and peak shift ratio, based on subtle changes in ion arrival times in the mass spectrometer, was introduced by Marsden et al (2018a) for the differentiation of mineral phases in silicates. Ternary sub-composition systems, such as (Al+Si) + -K + -Na + and Cl --(CN+CNO) --SO 4 -,were used to identify mineralogy and internal mixing state of ambient particles (Marsden et al, 2018b). In our previous study (Shen et al, 2018), laboratory-based reference spectra were suggested to be a useful tool for particle identification.…”