Abstract
Abstract. Soil erosion aerosols can be transported considerable distances, the Sahara being one of the major sources in the world. In June 2016 the volume scattering function of the atmospheric aerosol was determined in the Sierra Nevada, Spain, at an altitude of 2500 m. Measurements were performed with a polar nephelometer permitting measurements between scattering angles of 5 to 175∘. The values at the missing angles could be estimated to a high accuracy, using the shape of the scattering function adjacent to the missing angles, and thus a complete volume scattering function was available. During the measuring period intrusions of long-range transported Sahara aerosol happened several times. The classification of the aerosol was done by back trajectories and by the Angström exponent of the wavelength-dependent scattering coefficient, which was determined by a three-wavelength Integrating Nephelometer. The phase function of the Sahara aerosol had a stronger forward scattering, and less backscattering compared to the non-Sahara aerosol, which is in agreement with other findings for irregular particles. The asymmetry parameter of the phase function is the best characteristic to distinguish Sahara aerosol from non-Sahara aerosol. In this study the asymmetry parameter for the Sahara aerosol was larger than 0.65, whereas the non-Sahara aerosol had an asymmetry parameter below 0.6. A comparison with measurements performed with long-range transported Gobi desert aerosols observed in Kyoto, Japan, showed very similar results.
Highlights
Deserts are a major source of aerosol particles
The total PM10 emission of desert dust particle emissions was estimated as 1700 Tg yr−1; the atmospheric loading of dust particles PM10 is estimated as 20 Tg (Kok et al, 2017)
The volume scattering function of the atmospheric aerosol was measured in the Sierra Nevada, where intrusions of Sahara aerosol are frequent
Summary
Deserts are a major source of aerosol particles. On a global scale desert aerosol contributes 60–1800 Tg yr−1 of the total yearly aerosol production of 2900–4000 Tg (Jaenicke, 1988). Junge (1979) estimates the global source strength of deserts as 260 to 400 Tg yr−1, with the Sahara contributing 60 to 200 Tg yr−1. Zender et al (2004), using all estimates published between 2001 and 2004, give a range of global dust emissions of between 1000 and 2150 Tg yr−1. On a global scale desert aerosol contributes 60–1800 Tg yr−1 of the total yearly aerosol production of 2900–4000 Tg (Jaenicke, 1988). Junge (1979) estimates the global source strength of deserts as 260 to 400 Tg yr−1, with the Sahara contributing 60 to 200 Tg yr−1. Zender et al (2004), using all estimates published between 2001 and 2004, give a range of global dust emissions of between 1000 and 2150 Tg yr−1. The total PM10 (particles smaller than 10 μm) emission of desert dust particle emissions was estimated as 1700 Tg yr−1; the atmospheric loading of dust particles PM10 is estimated as 20 Tg (Kok et al, 2017). The clay-sized particles (diameter smaller than 2 μm) are an important subgroup due to their efficient light scattering, but account only for 3.5 % to 5.7 % of the PM10 emissions
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