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.
XIA DunSheng1,2, YANG LiPing2, MA JianYing1, YU Ye1, WANG Guan2 & CHEN FaHu2 1 Key Laboratory of Desert and Desertification, Institute of Cold and Arid Regions Environmental and Engineering, Chinese Academy of Sciences, Lanzhou 730000, China
通过对新疆巴里坤湖的地层剖面进行的精确定年和孢粉分析,结合现代表土孢粉数据,重建了该地区16.7cal ka BP以来的植被和环境演化历史.结果表明,在末次冰消期及早全新世(16.7～7.9cal ka BP)研究区以荒漠植被为主,A/C值所指示的有效湿度明显偏低,气候干旱.其中在16.7～8.9cal ka BP期间,气候环境最为恶劣;8.9～7.9cal ka BP为气候环境逐渐改善的过渡期.研究区在中全新世(7.9～4.3cal ka BP)为荒漠草原/草原,有效湿度明显升高,气候环境相对最为适宜,湖泊周围高地可能有片状的桦木林地出现.在4.3～3.8cal ka BP这一短暂时期,研究区植被由荒漠草原/草原迅速转变为荒漠,有效湿度显著降低,可能是一次百年尺度的干旱气候事件.研究区在晚全新世(3.8～0.53cal ka BP)呈现出典型的荒漠草原/草原草甸景观,有效湿度相对较高,气候环境相对较为适宜;0.53cal ka BP以来,呈现荒漠植被景观.区域对比显示,该地区16.7cal ka BP以来的气候环境演化特征与东亚季风影响区有着明显的差异,在末次冰消期-早全新世气候干旱,中全新世-晚全新世气候相对湿润.
Three ring-width chronologies were developed from Qilian Juniper （Sabina przewalskii Kom.） at the upper treeline along a west-east gradient in the Anyemaqen Mountains. Most chronological statistics, except for mean sensitivity （MS）, decreased from west to east. The first principal component （PC1） Ioadings indicated that stands in a similar climate condition were most important to the variability of radial growth. PC2 Ioadings decreased from west to east, suggesting the difference of tree-growth between eastern and western Anyemaqen Mountains. Correlations between standard chronologies and climatic factors revealed different climatic influences on radial growth along a west-east gradient in the study area. Temperature of warm season （July-August） was important to the radial growth at the upper treeline in the whole study area. Precipitation of current May was an important limiting factor of tree growth only in the western （drier） upper treeline, whereas precipitation of current September limited tree growth in the eastern （wetter） upper treeline. Response function analysis results showed that there were regional differences between tree growth and climatic factors in various sampling sites of the whole study area. Temperature and precipitation were the important factors influencing tree growth in western （drier） upper treeline. However, tree growth was greatly limited by temperature at the upper treeline in the middle area, and was more limited by precipitation than temperature in the eastern （wetter） upper treeline.
