Self‐attenuation artifacts and correction factors of light element measurements by X‐ray analysis: Implication for mineral dust composition studies

Abstract

[1] On a global scale, mineral dust is one of the major components of atmospheric aerosols and has important effects on the radiative budget of the atmosphere and thus on climate forcing. An accurate measurement of the concentration of crustal elements, namely Na, Mg, Al, Si, K, Ca, Ti, and Fe, is mandatory for the study of desert aerosols. The concentration of light elements, when measured by X-ray emission techniques such as X-ray fluorescence (XRF) and particle-induced X-ray emission (PIXE), can be underestimated owing to self-absorption of the emitted soft X-rays inside aerosol particles. In this work, we analyzed dust samples collected in field campaigns and samples produced in the laboratory using dust of known composition. Measurements have been conducted with PIXE and energy-dispersive XRF (ED-XRF), together with an attenuation-free technique such as particle-induced gamma-ray emission (PIGE) and attenuation corrected wavelength-dispersive XRF (WD-XRF) by internal standard calibration. We focus on the determination of Al and present results of a PIXE versus PIGE intercomparison. Aluminum concentration was measured with both techniques in dust samples collected by aircraft sampling over western Africa during winter 2006 and summer 2007. An underestimation of the Al concentration determined by PIXE was observed (up to 40%), and it was compared with the results of a simple calculation using basic physics and the size distribution of the collected aerosol. Similar attenuation was observed for Mg, Al, and Si in the laboratory samples analyzed by ED-XRF and WD-XRF. In order to use concentration ratios involving light elements as tracers of the region of emission of the sampled dust, these artifacts (i.e., underestimation of the concentration of light elements) induced by self-attenuation should be properly considered and corrected.Citation: Formenti, P., S. Nava, P. Prati, S. Chevaillier, A. Klaver, S. Lafon, F. Mazzei, G. Calzolai, and M. Chiari (2010), Self-attenuation artifacts and correction factors of light element measurements by X-ray analysis: Implication for mineral dust composition studies,

Spatial and seasonal distribution of aerosol chemical components in New York City: (2) Road dust and other tracers of traffic-generated air pollution

“…Data were averaged from all of the residential locations for each season. Markers of roadway dust, such as Al, Si, Fe, and Ti (Limbeck et al, 2009;Formenti et al, 2010), were generally elevated on the GWB walkways compared with the residential locations. It should be noted that the nearroadway measurements had significant variability as noted by the relatively wide SD; this is due, in part, to having data on just seven sampling periods at this location, compared with 4150 samples for each season of the residential data set.…”

Physico‐chemical and optical properties of Sahelian and Saharan mineral dust: in situ measurements during the GERBILS campaign

“…Elemental tracers of mineral dust, such as Al, Si, K, Ca, Ti and Fe, dominated the aerosol load, their sum in the oxide form accounting for up to 70% of the total gravimetric mass. However, if no correction is applied, Al and Si concentrations as determined by PIXE are surely underestimated because of self-attenuation of the emitted X-rays due to the particle size Formenti et al, 2010); if this effect is properly taken into account, the contribution of mineral dust to the total aerosol load increases to approximately 87%. In addition, a contribution of marine aerosol up to 7% was evident on 27 samples collected close to the Atlantic coast by the linear correlation of Na and Cl (coefficient of linear correlation R 2 = 0.82).…”

Spectral- and size-resolved mass absorption efficiency of mineral dust aerosols in the shortwave spectrum: a simulation chamber study

“…Thanks to the uniformity of the aerosol deposit on the filters, the atmospheric elemental concentrations (µg m −3 ) were calculated by multiplying the analyzed elemental mass thickness by the ratio between the collection and analyzed surfaces of each sample (41 and 22 mm, respectively), then dividing by the total sampled volume (m 3 ). Finally, concentrations of light-weight elements (atomic number Z < 19) were corrected for the underestimation induced by the selfabsorption of the emitted soft X-rays inside aerosol particles according to Formenti et al (2010). Additional XRF analysis of the quartz filters was performed both in the PM 10.6 and the PM 2.5 fractions to verify the absence of biases between the experiments dedicated to the determination of particle composition and those where the optical properties were measured.…”