Aerosol characterization at the Saharan AERONET site Tamanrasset

Abstract

Abstract. More than 2 years of columnar atmospheric aerosol measurements (2006)(2007)(2008)(2009) at the Tamanrasset site (22.79 • N, 5.53 • E, 1377 m a.s.l.), in the heart of the Sahara, are analysed. Aerosol Robotic Network (AERONET) level 2.0 data were used. The KCICLO (K is the name of a constant and ciclo means cycle in Spanish) method was applied to a part of the level 1.5 data series to improve the quality of the results. The annual variability of aerosol optical depth (AOD) and Ångström exponent (AE) has been found to be strongly linked to the convective boundary layer (CBL) thermodynamic features. The dry-cool season (autumn and winter) is characterized by a shallow CBL and very low mean turbidity (AOD ∼ 0.09 at 440 nm, AE ∼ 0.62). The wet-hot season (spring and summer) is dominated by high turbidity of coarse dust particles (AE ∼ 0.28, AOD ∼ 0.39 at 440 nm) and a deep CBL. The aerosol-type characterization shows desert mineral dust as the prevailing aerosol. Both pure Saharan dust and very clear sky conditions are observed depending on the season. However, several case studies indicate an anthropogenic fine mode contribution from the industrial areas in Libya and Algeria. The concentration weighted trajectory (CWT) source apportionment method was used to identify potential sources of air masses arriving at Tamanrasset at several heights for each season. Microphysical and optical properties and precipitable water vapour were also investigated.

A new zenith-looking narrow-band radiometer-based system (ZEN) for dust aerosol optical depth monitoring

“…We have identified the desert aerosol conditions following the criteria given in Guirado (2014), and Guirado et al (2014) (Sect. 2.1).…”

“…Taking into account previous studies in the literature Basart et al, 2009;Guirado et al, 2014;Cesnulyte et al, 2014;Cuevas et al, 2015) and AERONET climatology tables (https://aeronet.gsfc.nasa.gov/cgi-bin/climo_ menu_v2_new), AOD desert stations such as Tamanrasset (Algeria), Ouarzazate (Morocco), Dakar (Senegal) and Solar Village (Saudi Arabia) show monthly and seasonal values typically ranging between 0.04 (Ouarzazate in January) and 0.67 (Dakar in June), with sporadic AOD maxima > 1 associated with strong desert dust outbreaks or local dust resuspension. Therefore, we have focused our sensitivity study in AOD conditions varying between 0.5, which corresponds to hazy conditions by dust, and 1, indicating strong dust intrusions.…”

“…As Basart et al (2009) (Basart et al, 2009), increasing AOD and reducing α values. Following the work developed by Guirado et al (2014), those situations with AOD 500 nm > 0.15 and α < 0.5 can be considered prevalent dust conditions at this station.…”

“…is located in southern Algeria in a key location near the most important dust sources of Mali, Argelia, Lybia and Chad, where there is little impact from industrial activities. Guirado et al (2014) performed a thorough study to characterize aerosols at this Saharan station. They found that desert mineral dust is the predominant aerosol type in this station, where the dry-cool (winter) season is characterized by prevailing clear-sky conditions (AOD 440 nm ∼ 0.09 and α ∼ 0.62), while high turbidity events with coarse dust particles are frequent during the wet-hot (summer) season, associated to an AOD 440 nm modal value of 0.15 and α ∼ 0.4.…”

Evaluation of climate model aerosol seasonal and spatial variability over Africa using AERONET

“…In many places, biomass burning aerosols dominate the seasonal cycle of the aerosol column in the region (Tesfaye et al, 2011;Queface et al, 2011;Sivakumar et al, 2010;, which in turn can have a significant impact on the regional climate (Abel et al, 2005;Winkler et al, 2008;Tummon et al, 2010). Although these two sources dominate total column aerosol in Africa, fine anthropogenic aerosols are also observed, including at sites in the Sahara desert and off the coast of northern Africa (Rodríguez et al, 2011;Guirado et al, 2014).…”