Temporal trends in agricultural water use and the relationships to hydroclimatic factors in the High Plains aquifer region

The High Plains aquifer (HPA) is the primary water source for agricultural irrigation in the US Great Plains. The water levels in many locations of the aquifer have declined steadily over the past several decades because the rate of water withdrawals exceeds recharge, which has been a serious concern to the water resources management in the region. We evaluated temporal trends and variations in agricultural water use and hydroclimatic variables including precipitation, air temperature, reference evapotranspiration, runoff, groundwater level, and terrestrial water storage across the HPA region for different periods from 1985 to 2020 at the grid, county, or region scale. The results showed that water withdrawals decreased from 21.3 km³/year in 1985 to 18.2 km³/year in 2015, while irrigated croplands increased from 71,928 km² in 1985 to 78,464 km² in 2015 in the entire HPA. The hydroclimatic time-series showed wetting trends in most of the northern HPA, but drying and warming trends in the southern region from 1985 to 2020. The groundwater level time-series indicated flat trends in the north, but significant declining in the central and southern HPA. Trends in irrigation water withdrawals and irrigation area across the HPA were controlled by the advancement of irrigation systems and technologies and the management of sustainable water use, but also were affected by dynamical changes in the hydroclimatic conditions.     

2014年北京市CO浓度水平和时空分布

对北京市地面监测站点的CO浓度进行分析，探讨其浓度水平、变化趋势和时空分布特征。2014年春、夏、秋、冬四季北京市CO平均浓度分别为1.06、0.87、1.34、2.17 mg/m³。CO浓度均呈双峰型变化，第一个峰值出现在07：00-09：00，主要由交通早高峰的排放引起；第二个峰值出现在23：00左右，主要受交通晚高峰排放和夜间边界层高度降低的挤压效应的共同影响。从空间分布来看，全年整体呈现南高北低的分布特征，尤其是秋、冬季较为明显，体现了工业布局和区域传输对CO的影响。从全年来看，湿度对CO浓度的影响最大。对2014年冬季北京市的一次高CO浓度分析结果表明，此次过程是由本地排放和区域传输共同造成的，气象要素中地面气压对CO浓度影响最大。     

县域城镇空气质量变化与防治对策分析研究

摘要：对2006～2011年宜良县城NO2、SO2、PM10监测数据进行统计分析,认为SO2是县城的主要污染物。3种污染物年际浓度变化为：NO2、SO2下降趋势显著,PM10下降趋势不显著;季节浓度变化为：S02冬〉秋〉春〉夏,N02、PM10冬〉春〉秋〉夏,并提出防治建议。     

中国突发环境事件时间序列分析

突发性环境事件时间序列特征可表征环境风险管理成效及存在问题。研究表明2000年以来中国突发环境事件预防、控制与管理取得了显著成效,其中,突发性水污染事件、大气污染事件以及噪声振动危害年发生频次呈大幅度降低趋势,但固废污染事件自2003年以来的年发生频次变化不大,而其它突发性环境事件自2002年以来的年发生频次则呈快速增长态势,说明中国在强调突发性水环境和大气环境事件监管的同时,还需加强固废污染事件及其它类型突发环境事件的监控与管理。     

中国环境风险现状及发展趋势分析

基于国内2000-2009年以来环境污染事故统计资料,深入分析了中国现阶段环境风险类型、事故高发区域、事故损失、环境风险事故诱因等特征,并对其环境风险演变趋势进行了判断。新时期中国经济增长方式处于转变阶段,以布局型环境隐患和结构型环境风险为首要威胁,风险类型更加复杂化,事故影响范围进一步扩大,由于居民消费转型与科技发展带来的新型环境风险更是不可预知,环境风险压力进一步增大。     

天津市环境空气中一氧化碳污染特征及变化趋势研究

文章通过对2010年天津市12个环境空气质量监测国控点(不含清洁对照点)实时连续监测的CO数据的深入分析,探讨了其浓度趋势变化和污染特征。结果表明:CO日变化规律呈典型的双峰型,冬季CO浓度最高,夏季最低,CO与O3和温度均呈较好的负相关性。     

上海市闸北区城市河道水质演变规律和新出现的问题

通过对十年来上海市闸北区范围内彭越浦、走马塘和西泗塘三条河道上的四个监测断面的水质监测数据,选取高锰酸盐指数、化学需氧量、生化需氧量、氨氮、石油类、总磷和挥发酚七项指标,运用水质综合指数法探讨了水质变化趋势、时空变化特征、主要污染因子及其变化趋势,在发现水质显著改善的同时,对新出现的问题进行了探讨。     

几种网格数据处理方法的应用与评述

对于利用网格布点所测得数据的处理,可采用积分法、趋势面法、多项式法和平均值法,各种处理方法各有其特点。平均值法计算简单,各个网格权重相同,意义明了,但精度不高;积分法和趋势面法考虑到了位于中心的网格对整个区域的贡献率大,组成的三角形多,统计时利用次数就多,边缘的网格数据利用次数少,物理意义明确。积分法还可计算总量,趋势面法可以在图上表示区域分布及变化趋势;多项式法除了计算其平均值外,还可模拟测定值,可计算测得数值序列趋势值和偏差值,分析污染物分布及变化情况。使用时要根据分析对象的物理意义及研究目的不同,选择不同的数学模型和计算公式。     

Seasonal trend of ambient PCDD/Fs in Tianjin City, northern China using active sampling strategy

The spatial concentrations, seasonal trends, profiles and congener pairs of ambient polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs) were investigated within a seasonally active sampling scheme during Jun 2008 and Jan 2009 in Tianjin City, northern China. The PCDD/F concentrations ranged 14.2-172 fg I-TEQ/m³ (average 69.3 fg I-TEQ/m³) in summer and (89.8-1.01) × 10³ fg I-TEQ/m³ (average 509 fg I-TEQ/m³) in winter, respectively, except for the E-waste dismantling site where much higher values were observed (1.04 × 10³ fg I-TEQ/m³ in summer and 7.123 × 10³ fg I-TEQ/m³ in winter). The results indicated a significantly seasonal trend with higher TEQ values in winter as compared with summer, which could be related to increased emission sources and seasonal variations of the atmospheric boundary layer height. 2,3,4,7,8-PeCDF was the dominant contributor to the total PCDD/F toxic equivalents, and 2,3,7,8-TCDD was detected at almost all the sampling sites in winter. Most of the similarly substituted PCDD/F congener pairs exhibited high correlations, suggesting that they might have similar environmental fate or sources. But different seasonal and spatial distributions of PCDD/F concentrations indicated that the emission sources might be intermittent.     

Characteristics and recent trends of sulfur dioxide at urban, rural, and background sites in North China: Effectiveness of control measures

SO₂ measurements made in recent years at sites in Beijing and its surrounding areas are performed to study the variations and trends of surface SO₂ at different types of sites in Northern China. The overall average concentrations of SO₂ are (16.8 ± 13.1) ppb, (14.8 ± 9.4) ppb, and (7.5 ± 4.0) ppb at China Meteorological Administration (CMA, Beijing urban area), Gucheng (GCH, relatively polluted rural area, 110 km to the southwest of Beijing urban area), and Shangdianzi (SDZ, clean background area, 100 km to the northeast of Beijing urban area), respectively. The SO₂ levels in winter (heating season) are 4-6 folds higher than those in summer. There are highly significant correlations among the daily means of SO₂ at different sites, indicating regional characteristics of SO₂ pollution. Diurnal patterns of surface SO₂ at all sites have a common feature with a daytime peak, which is probably caused by the downward mixing and/or the advection transport of SO₂-richer air over the North China Plain. The concentrations of SO₂ at CMA and GCH show highly significant downward trends (-4.4 ppb/yr for CMA and -2.4 ppb/yr for GCH), while a less significant trend (-0.3 ppb/yr) is identified in the data from SDZ, reflecting the character of SDZ as a regional atmospheric background site in North China. The SO₂ concentrations of all three sites show a significant decrease from period before to after the control measures for the 2008 Olympic Games, suggesting that the SO₂ pollution control has long-term effectiveness and benefits. In the post-Olympics period, the mean concentrations of SO₂ at CMA, GCH, and SDZ are (14.3 ± 11.0) ppb, (12.1 ± 7.7) ppb, and (7.5 ± 4.0) ppb, respectively, with reductions of 26%, 36%, and 13%, respectively, compared to the levels before. Detailed analysis shows that the differences of temperature, relative humidity, wind speed, and wind direction were not the dominant factors for the significant differences of SO₂ between the pre-Olympics and post-Olympics periods. By extracting the data being more representative of local or regional characteristics, a reduction of up to 40% for SO₂ in polluted areas and a reduction of 20% for regional SO₂ are obtained for the effect of control measures implemented for the Olympic Games.