Current Situation of Heavy Metal Pollution in Soil and Dustfall in Some Cities of China

Because of human activities, urban dustfall and soil in China have been polluted by heavy metals in different degrees. However, the type and pollution degree of heavy metal hazard are different among cities. Based on data about the heavy metal pollution of urban soil and dustfall as well as related information inves- tigated, the present situation of heavy metal pollution in soil and dustfall in 23 regions of China were summarized, and some suggestions were put forward accord- ing to the existing problems of research on heavy metal pollution, aiming to provide reference for government decision-making and related research in future.

Effects of geomorphic conditions, wind speed, and precipitation on dustfall over northern China

We investigated how dustfall flux (DF) and dust particle size (DPS) were affected by geomorphic conditions, wind speed, and precipitation using data from 27 sites in northern China. The sites with the greatest DF and greatest median diameter of dustfall (MDD) were primarily in desert regions and had extensive mobile sands. DF and MDD were lowest in agricultural regions, which had low levels of coarse particles because of human land use and high vegetation coverage that restrained blowing sand. DF values were higher and MDD values were lower in the western agricultural region than in the eastern agricultural region because the former is closer to desert regions and contains more fine dust that has traveled far. In regions with extensive desertified lands, DF values were lower than those in desert regions, and MDD values were greater than in agricultural regions, possibly due to coarsening of soil texture by desertification processes combined with higher vegetation coverage and soil moisture than in desert regions, thereby restraining blowing sand. Although high DF and MDD always coincided spatially with strong winds and low precipitation, the strong winds and low precipitation did not always mean high DF and MDD. High DF also coincided temporally with periods of low precipitation, but low precipitation did not always mean high DF. Thus, although the spatial trends in DF and DPS were controlled mostly by geomorphic conditions, and monthly trends in DF were controlled mainly by wind speed, weak wind and high precipitation can restrain the blowing sand at certain times and locations. Seasonal changes in DPS may be controlled simultaneously by geomorphic conditions, meteorological factors, and distance from source areas, not solely by the winter monsoon.

Spatial trends of dustfall over northern China in the spring and their influencing factors

The spatial trends of dustfall of different sizes over northern China during April and May 2001,and March 2002,and their influencing factors,were analyzed.We divided the dustfall into seven grades based on particle size.Total dustfall and dustfall for each grade were highest in desert regions then in regions undergoing desertification,and the total dustfall,dustfall 【100 μm and dustfall 】250 μm were higher in western agricultural regions closer to desert areas than in eastern agricultural regions.The spatial trends in dustfall 【300 μm in diameter were most strongly correlated with dust events,and the content of coarse particles increased with increasing severity of dust events.Because the spatial trend for dust events appears to be controlled by geomorphic conditions,vegetation coverage,soil moisture,and the distance from dust source,dustfall 【300 μm in diameter appears to have the same controlling factors as dust events,but the control decreases with increasing particle size.Wind,the driving force for dust emissions,also influenced the spatial trends in dustfall 【200 μm in diameter,and especially for dustfall 50 to 100 μm in diameter.Although dustfall 【300 μm in diameter and precipitation were not strongly spatially correlated,there is some evidence that high precipitation decreased deposition by restraining blowing sand.The coarser the dustfall,the weaker the correlation with wind speed;however,transport of larger particles still occurs,and further research will be required to test the possibility that this dust is entrained mainly by the small-scale dust devils that are commonly observed in the study area.

Dustfall Associated with Dust Storms in the Al-Ahsa Oasis of Saudi Arabia

Dustfall is a major threat to agricultural and industrial infrastructures, as well as to other aspects of livelihood. Dustfall associated to a severe dust storm that hit the Al-Ahsa Oasis of Saudi Arabia during 12-13 March 2014 is discussed in this paper. The storm caused widespread and heavy dust deposition. A dramatic decrease in the visibility coincided with the storm, and the average dust concentrations recorded during a peak 10-hour period were 6772, 5862.4 and 451.1 μg/m3 for total suspended particles (TSP), particulate matter smaller than or equal to 10 μm (PM10) and those smaller than or equal to 2.5 μm (PM2.5), respectively. The lowest visibility was 200 m, and the wind speed increased to 17.5 m/s from the north. The average daily dust deposited in the study area during the event was 12.84 (SD = 1.2) g/(m2?d). The dust samples comprised insoluble dust (48.5%) and soluble dust (51.5%). Based on the Munsell color system, the final color description of the falling dust was 10 YR/6/3. A microphotograph of the dustfall (settleable particulate matter) captured by a stereo dissection microscope shows that the dust particles had various colors and sizes, and they contained fibers and vegetative debris).

Foliar Dust Size Characteristics of Greening Trees in Aksu, Northwest China

Urban greening trees intercept the migration of atmospheric particulate matters near the ground, and it is difficult for the particulate matters trapped by foliage to re-elevate, thus reducing the hafm to humans. The dust-capturing ability and foliar dust size charactetistics of different greening trees are different In addition, the dust capturing of trees is distutbed by many factors such as sel natural and human factors. The foliar dust and natural dustfaJl in 11 common, tree species in Aksu, Northwest China were collected to analyze tihe particle size distribution diacacteristics,and obtain the concentrations of PM^ and PM10. The results showed that Pktanus acenfolia, Populus alba var. pyramidaJis and Uhnus densa. had high foliar dust attachment density and strong particle-capturing capacity,while Elaeagnus angustifoliaL., Pyrns sinldangensis, Sophora japonica L. had low foliar dust attachment density. The foliar PMZ5 and PM10 contents were highest in E. ongustifolia （0.68%） and Vitis vinefcra （3.59%）, tespectively. The volume fraction of fine partides was small in natural dustM and was kige in foliar dust The median of foliar dust particle size followed tiie descending ordei： industrial area 〉 transportation hub area 〉 residential area 〉 clean area; and the median of natural dustfall particle size followed the descending order： dear area 〉 transportation hub area 〉 industrial area 〉 residential area. There was a big difference between the two.

Atmospheric iron deposition in a megacity of northwest China:Solubility,speciation,and deposition fluxes

Atmospheric iron has crucial effects on biogeochemical cycles,atmospheric processing,global climate,and human health.In this study,atmospheric dustfall samples were collected from six functional areas in Xi'an,China,from 2020 to 2021.The spatiotemporal distributions and deposition fluxes of total and water-soluble(ws)Fe as well as the speciation and potential sources of ws-Fe were characterized.Industrial areas had the highest concentrations of total Fe and ws-Fe,which were mainly due to copious emissions of heavy metals during manufacturing.The total Fe concentrations peaked in spring,primarily due to the substantial input of crustal dust,which also led to the lowest Fe solubility in this season.By contrast,the highest levels of ws-Fe occurred during winter due to an increase in biomass combustion.Among the water-soluble forms,ws-Fe(II)was dominant and accounted for 74.8%of the total amount of ws-Fe.Crustal dust was the main contributor to total Fe,whereas biomass burning primarily contributed to peak ws-Fe concentrations.The average total and ws-Fe deposition fluxes in Xi'an were the highest in spring and lowest in autumn,which were related to the distributions of the dustfall deposition fluxes and their Fe contents during these periods.Our study provided a broader and comprehensive understanding of atmospheric iron deposition in Chinese urban area,which is of positive significance for understanding atmospheric chemistry and global climate change.

Pollution characteristics of atmospheric dustfall and heavy metals in a typical inland heavy industry city in China

Through field sampling of atmospheric dustfall in regions of Zhuzhou City, China for a period of one year, the deposition fluxes of atmospheric dustfall and five heavy metals contained inside, including Cr, As, Cd, Hg and Pb, were analyzed. Meanwhile the enrichment factor and index methods were used to analyze the pollution characteristics of heavy metals of atmospheric dustfall in Zhuzhou. The annual deposition flux of atmospheric dustfall in Zhuzhou was 50.79 g/（m^2.year）, while the annual deposition fluxes of Cr, As, Cd, Hg and Pb were 9.80, 59.69, 140.09, 0.87 and 1074.91 mg/（m^2.year）, respectively. The pollution level of atmospheric dustfall in Zhuzhou was relatively lower compared with most other cities in China, but the deposition fluxes of As, Cd, Hg and Pb in atmospheric dustfall in Zhuzhou were much higher than that in most cities and regions around the world. Cd is the typical heavy metal element in atmospheric dustfall in Zhuzhou, and both the enrichment factor and pollution index of Cd were the highest. Cd, Hg, Pb and As in atmospheric dustfall were mainly from human activities. According to the single-factor index, Nemerow index and pollution load index analyses, the atmospheric dustfall in Zhuzhou could easily cause severe heavy metal pollution to urban soil, and the most polluting element was Cd, followed by Pb, As and Hg. Only the pollution level of Cr lay in the safety region and mainly originated from natural sources.

Magnetic characteristics of dustfall in urban area of north China and its environmental significance

Urban particulate pollutants not only affect urban air quality but also directly threaten public health. Lanzhou has been one of the most seriously polluted cities in the world due to its special geophysical location and weather conditions, which makes it an ideal place for urban particulate pollution study. In this study a set of environmental magnetic parameters (χ_(1f),χ_(fd)%, χ_(ARM), SIRM, HIRM, SOFT and back field IRM) were measured and analyzed for the dustfall samples collected monthly during 1997.4—2000.5 and 2004.11—2005.10 at Lanzhou University campus (KLD and CCS) and at a clear site of Gaolanxian (GLX). Results demonstrate that the main magnetic minerals in the dustfall are magnetite, with some maghaemite and haematite. Cross plots of M_(rs)/M_s vs. B_(cr)/B_c and χ_(fd)% vs. χ_(ARM)/SIRM indicate that the main magnetic grain sizes are pseudo-single-domain (PSD). The high concentration of magnetic minerals in the dustfall indicates that Lanzhou is seriously polluted. The main pollution sources are anthropogenic activities and nature dust, with the former posing a great threat during the whole year, which is different from the general view that the natural dust is the main contributor in summer. With great efforts of the government and local authority in the past decades, the air quality in Lanzhou has been improved in winter, but it is not so obvious in summer. This study also reveals that as a simple, rapid and accurate technology, environmental magnetism could be a valuable tool for urban pollution study.