Chemical characteristics of precipitation and the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain, northwestern China

Precipitation chemistry analysis is essential to evaluate the atmospheric environmental quality and identify the sources of atmospheric pollutants. In this study, we collected a total of 480 precipitation samples at 6 sampling sites in the northern and southern slopes of Wushaoling Mountain from May 2013 to July 2014 to analyze the chemical characteristics of precipitation and to identify the main sources of ions in precipitation. Furthermore, we also explored the indicative significance for sand dust events in the northern and southern slopes of Wushaoling Mountain based on the precipitation chemistry analysis.During the sampling period（from May 2013 to July 2014）, the p H values, EC（electrical conductivity）values and concentrations of cations（Ca^（2＋）, Mg^（2＋）, Na~＋, K~＋ and NH_4~＋） and anions（SO_4^（2–）, NO_3~–, Cl~–, NO_2~– and F~–） in precipitation were different in the northern and southern slopes at daily and seasonal time scales, with most of the values being higher in the northern slope than in the southern slope. The chemical type of precipitation in the southern and northern slopes was the same, i.e.,SO_4^（2–）-Ca^（2＋）-NO_3~–-Na~＋. The concentrations of ions in precipitation were mainly controlled by terrigenous material and anthropogenic activities（with an exception of Cl~–）. The concentration of Cl~– in precipitation was mainly controlled by the sea salt fraction. The concentrations of Na＋ and Cl~– showed an increasing trend after the occurrence of sand dust events both in the northern and southern slopes. In addition, after the occurrence of sand dust events, the concentrations of K~＋, Mg^（2＋）, SO_4^（2–）, NO_3~– and Ca^（2＋） showed an increasing trend in the southern slope and a decreasing trend in the northern slope. It is our hope that the results may be helpful to further understand the atmospheric pollution caused by sand dust events in the Wushaoling Mountain and can also provide a scientific basis for the effective prevention of atmospheric pollution.

Biological crust in sand and dust storm source areas of Asia and its impact on dust emission

Even though the biological crusts are critical to dust emissions,no sand and dust forecast model have considered the impacts of the biological crust in dust emission scheme.This situation mainly comes from two scientific difficulties:there is no large scale regional biological crust data available that can be used in the forecast model;there is no quantification of how biological crusts impact on sand emission.In this way,we studied the distribution of biological soil crust in sand and dust storm source areas of Central and East Asia using Moderate Resolution Imaging Spectroradiometer satellite surface reflectance data collected in 2000—2019 to determine its potential impact on dust emission according to two empirical schemes.We further evaluated the relationships between soil crust coverage,roughness length,and dust emission to study SDS source areas.We found that biological crust is widely distributed in SDS source areas of Central and East Asia,with coverage rates of 19.8%in Central Asian deserts,23.1%in the Gobi Desert,and 17.3%—32.8%in Chinese deserts(p>0.05).Cyanobacteria and lichen coverage has increased in Chinese deserts,reflecting the recent impacts of the Project of Returning Farmland to Grassland and Farmland to Forests.However,biological soil crust coverage has not increased in Central Asian deserts or the Gobi Desert,and that in Central Asian deserts continues to decrease,demonstrating the complexity of the combined effects of human activities and climate change on its distribution.Biological soil crust increased the roughness length of Central and East Asian SDS source areas by 0.14—0.62 mm.The suppression of dust emission due to biological soil crust did not change among years during the study period.The horizontal and vertical dust flux inhibition coefficient(DFIC)were 2.0—11.0 and 1.7—2.9(p>0.05),respectively,clearly showing a suppressive effect.Improvement of the ecological environment in some deserts can lead to the ability of these crusts to inhibit dust erosion errors that must be considered in the dust emission scheme for areas where crust coverage has improved.

Source,route and effect of Asian sand dust on environment and the oceans

We summarize in this overview achievements in current research frontiers in Asian sand dust with emphasis on the method for sand dust research, the sources of sand dust aerosols, emission of sand dust, mechanism of sand dust weather, chemical transformation during transport, and influences on climatic environment and oceans. Our main results show that most of Asian sand dust comes from Mongolia, the Gobi Desert, arid and semiarid desert areas in northwest China, which is divided into initial sources and enhanced sources. Half of the global production of dust originates from Asian dust source regions. Asian dust weather is so immense that it can cover a 5-？-day journey from the sources to the Korean Peninsula, Japan Islands, and the Pacific Ocean to even impact North America. Asian dust weather plays an active role in the hiogeochemical cycles of trace elements in the mid-latitude Northern Hemisphere.