Saharan dust events at the Jungfraujoch: detection by wavelength dependence of the single scattering albedo and first climatology analysis

Abstract

Abstract. Scattering and absorption coefficients have been measured continuously at several wavelengths since March 2001 at the high altitude site Jungfraujoch (3580 m a.s.l.). From these data, the wavelength dependences of the Angström exponent and particularly of the single scattering albedo are determined. While the exponent of the single scattering albedo usually increases with wavelength, it decreases with wavelength during Saharan dust events (SDE) due to the greater size of the mineral aerosol particles and their different chemical composition. This change in the sign of the single scattering exponent turns out to be a sensitive means for detecting Saharan dust events. The occurrence of SDE detected by this new method was confirmed by visual inspection of filter colors and by studying long-range backtrajectories. An examination of SDE over a 22-month period shows that SDE are more frequent during the March-June period as well as during October and November. The trajectory analysis indicated a mean traveling time of 96.5 h, with the most important source countries situated in the northern and north-western part of the Saharan desert. Most of the SDE do not lead to a detectable increase of the 48-h total suspended particulate matter (TSP) concentration at the Jungfraujoch. During Saharan dust events, the average contribution of this dust to hourly TSP at the Jungfraujoch is 16 µg/m 3 , which corresponds to an annual mean of 0.8 µg/m 3 or 24% of TSP.

Ice nuclei properties within a Saharan dust event at the Jungfraujoch in the Swiss Alps

“…It is important to mention that hematite which could be found in mineral dust is another compound that can significantly absorbs light. It usually has a small contribution to the total absorption coefficient in pristine days, but significantly changes the absorption coefficient when high dust load are present (Collaud Coen et al, 2004). Further information about σ abs,BC measurements with the MAAP at the Jungfraujoch can be found in Cozic et al (2008b).…”

“…They found during CLACE-3 an average concentration of several hundreds ice residuals per liter in one cloud on 24 March 2004 using an ice-CVI. Our measurement campaigns were also motivated by the high probability of Saharan Dust Events (SDE) between March and June (Collaud Coen et al, 2004). This paper shows the first dataset of IN measurements at the JFJ over several days and discusses results of IN number concentration and its variation with respect to a SDE at the JFJ.…”

Relating aerosol absorption due to soot, organic carbon, and dust to emission sources determined from in-situ chemical measurements

“…Russell et al (2010) highlighted that many recent studies have shown the persistent connections between aerosol absorbing species and the wavelength dependence of absorption. Thus, numerous studies have classified absorbing aerosol types from optical properties measured on ground stations (Eck et al, 1999;Dubovik et al, 2002;Collaud Coen et al, 2004;Fialho et al, 2005;Meloni et al, 2006;Kalapureddy et al, 2009;Mielonen et al, 2009;Giles et al, 2011Giles et al, , 2012 and from satellites (Higurashi and Nakajima, 2002;Barnaba and Gobbi, 2004;Jeong and Li, 2005;Kaufman et al, 2005;Torres et al, 2005;Kaskaoutis et al, 2007;Kim et al, 2007;Yu et al, 2009). In this study, in-situ optical properties and single particle chemical composition measured during three aircraft field campaigns are combined in order to validate a methodology for the estimation of absorbing aerosol types using spectral optical properties.…”

The "dual-spot" Aethalometer: an improved measurement of aerosol black carbon with real-time loading compensation

“…At this wavelength, other aerosol particles (carbonaceous or mineral) absorb significantly less and absorption can be attributed to BC alone (Sandradewi et al, 2008a and b;Fialho et al, 2005;Yang et al, 2009;and references therein). Measurements at distinct spectral regions (370,470,520,590,660,880 and 950 nm) allow for spectral analysis of the data -the analysis of the dependence of absorption on the wavelength can be of importance for research on direct effects of aerosol BC, climate forcing (Bond et al, 2013;IPCC, 2013) or mineral dust detection (Collaud Coen et al, 2004), through the determination of the single scattering albedo dependence on the wavelength, or source apportionment (Sandradewi et al, 2008b). When the attenuation reaches a certain threshold, a tape advance is induced so that measurements start on a clean spot.…”