Abstract
Abstract. The Taklamakan desert is an important dust source for the global atmospheric dust budget and a cause of the dust weather in East Asia. The characterization of Taklamakan dust in the source region is still very limited. To fill this gap, the DAO (dust aerosol observation) was conducted in April 2019 in Kashi, China. The Kashi site is about 150 km from the western rim of the Taklamakan desert and is strongly impacted by desert dust aerosols, especially in spring time, i.e., April and May. According to sun–sky photometer measurements, the aerosol optical depth (at 500 nm) varied in the range of 0.07–4.70, and the Ångström exponent (between 440 and 870 nm) in the range of 0.0–0.8 in April 2019. In this study, we provide the first profiling of the 2α+3β+3δ parameters of Taklamakan dust based on a multiwavelength Mie–Raman polarization lidar. For Taklamakan dust, the Ångström exponent related to the extinction coefficient (EAE, between 355 and 532 nm) is about 0.01 ± 0.30, and the lidar ratio is found to be 45 ± 7 sr (51 ± 8–56 ± 8 sr) at 532 (355) nm. The particle linear depolarization ratios (PLDRs) are about 0.28–0.32 ± 0.07 at 355 nm, 0.36 ± 0.05 at 532 nm and 0.31 ± 0.05 at 1064 nm. Both lidar ratios and depolarization ratios are higher than the typical values of Central Asian dust in the literature. The difference is probably linked to the fact that observations in the DAO campaign were collected close to the dust source; therefore, there is a large fraction of coarse-mode and giant particles (radius >20 µm) in the Taklamakan dust. Apart from dust, fine particles coming from local anthropogenic emissions and long-range transported aerosols are also non-negligible aerosol components. The signatures of pollution emerge when dust concentration decreases. The polluted dust (defined by PLDR532≤0.30 and EAE355-532≥0.20) is featured with reduced PLDRs and enhanced EAE355−532 compared to Taklamakan dust. The mean PLDRs of polluted dust generally distributed in the range of 0.20–0.30. Due to the complexity of the nature of the involved pollutants and their mixing state with dust, the lidar ratios exhibit larger variabilities compared to those of dust. The study provides the first reference of novel characteristics of Taklamakan dust measured by Mie–Raman polarization lidar. The data could contribute to complementing the dust model and improving the accuracy of climate modeling.
Highlights
Airborne dust is the most abundant aerosol species and accounts for nearly 35 % of the total aerosol mass in the atmosphere (Boucher et al, 2013) with an annual flux of 1000– 5000 Tg per year (Engelstaedter et al, 2006; Textor et al, 2006; Huneeus et al, 2011)
Long-range transported dust could possess such particle linear depolarization ratios (PLDRs) due to the deposition of big particles in the transport. This case is classified as polluted dust because the PLDR below 0.30 at 532 nm and the increase in water vapor mixing ratio (WVMR) and EAE355−532 at the boundary layer top fit the characteristics of polluted dust better
In dust events (Case 1 and Case 2), dust particles are lifted from the Taklamakan desert by the low-pressure system along with strong wind and blown to the observation site by the easterly or northeasterly wind
Summary
Airborne dust is the most abundant aerosol species and accounts for nearly 35 % of the total aerosol mass in the atmosphere (Boucher et al, 2013) with an annual flux of 1000– 5000 Tg per year (Engelstaedter et al, 2006; Textor et al, 2006; Huneeus et al, 2011). A comprehensive dataset of dust properties is of significant importance for understanding the effects of dust on the ecosystem and for reducing the uncertainties of climate models This task is very challenging and needs the support of observational data. A multiwavelength Mie–Raman polarization aerosol lidar can obtain multiple parameters at a vertical level This capability makes it a useful tool for aerosol study. The earliest field campaign characterizing Asian dust dates back to 1989 when an experiment was carried out in Tajikistan for studying desert dust properties and the impact on meteorological conditions. A multiwavelength Mie–Raman polarization lidar was deployed in Dushanbe, Tajikistan This results in Hofer et al (2017) and Hofer et al (2020) provided important dust properties, such as vertically resolved lidar ratios, linear depolarization ratios and mass concentrations. In 2019, the DAO (dust aerosol observation) campaign was conducted from April to June in China.
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