Abstract
Abstract. Mineral dust aerosols (MDs) not only influence the climate by scattering and absorbing solar radiation but also modify cloud properties and change the ecosystem. From 3 April to 16 May 2014, a ground-based mobile laboratory was deployed to measure the optical and microphysical properties of MDs near dust source regions in Wuwei, Zhangye, and Dunhuang (in chronological order) along the Hexi Corridor over northwestern China. Throughout this dust campaign, the hourly averaged (±standard deviation) aerosol scattering coefficients (σsp, 550 nm) of the particulates with aerodynamic diameters less than 2.5 µm (PM2.5) at these three sites were sequentially 101.5 ± 36.8, 182.2 ± 433.1, and 54.0 ± 32.0 Mm−1. Correspondingly, the absorption coefficients (σap, 637 nm) were 9.7 ± 6.1, 6.0 ± 4.6, and 2.3 ± 0.9 Mm−1; single-scattering albedos (ω, 637 nm) were 0.902 ± 0.025, 0.931 ± 0.037, and 0.949 ± 0.020; and scattering Ångström exponents (Åsp, 450–700 nm) of PM2.5 were 1.28 ± 0.27, 0.77 ± 0.51, and 0.52 ± 0.31. During a severe dust storm in Zhangye (i.e., from 23 to 25 April), the highest values of σsp2.5 (∼ 5074 Mm−1), backscattering coefficient (σbsp2.5, ∼ 522 Mm−1), and ω637 (∼ 0.993) and the lowest values of backscattering fraction (b2.5, ∼ 0.101) at 550 nm and Åsp2.5 (∼ −0.046) at 450–700 nm, with peak values of aerosol number size distribution (appearing at the particle diameter range of 1–3 µm), exhibited that the atmospheric aerosols were dominated by coarse-mode dust aerosols. It is hypothesized that the relatively higher values of mass scattering efficiency during floating dust episodes in Wuwei and Zhangye are attributed to the anthropogenic soil dust produced by agricultural cultivations.
Highlights
The role of mineral dust aerosols (MDs) in the climate system has received considerable attention over recent years (Arimoto et al, 2006; Ramanathan et al, 2001; Li and Min, 2010)
Floating dust is generally defined as a weather phenomenon in which fine-mode dust particles are suspended in the lower troposphere under calm or low-wind conditions, with horizontal visibility less than 10 km, while a dust storm is when large quantities of dust particles are lofted by strong winds, and horizontal visibility is reduced to below 1 km (Wang et al, 2005, 2008)
The data collected during the strong dust storm in Zhangye are excluded, and all the aerosol-scattering-related parameters discussed here are for the wavelength of 550 nm
Summary
The role of mineral dust aerosols (MDs) in the climate system has received considerable attention over recent years (Arimoto et al, 2006; Ramanathan et al, 2001; Li and Min, 2010). In order to fully account for the climate effects of MDs over eastern Asian regions, several international intensive field campaigns were conducted to measure their optical, physical, and chemical properties in recent decades, for example, the Asian Aerosol Characterization Experiment (ACE-Asia) (Arimoto et al, 2006), the NASA Global Tropospheric Experiment Transport and Chemical Evolution over the Pacific (TRACE-P) (Jacob et al, 2003), the Atmospheric Brown Clouds–East Asia Regional Experiment (ABC-EAREX) (Nakajima et al, 2003), and the 2008 China–US joint dust field experiment (Ge et al, 2010; Li et al, 2010; Wang et al, 2010). The systematic review of the optical and microphysical properties of MDs in eastern Asia is still a challenge due to limited observations, especially for fine-mode mineral dust near the dust source areas in northwestern China
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