Analysis of the Trend and Seasonal Cycle of Carbon Monoxide Concentrations in an Urban Area (4 pp)

Background, Aim and Scope Air quality is an field of major concern in large cities. This problem has led administrations to introduce plans and regulations to reduce pollutant emissions. The analysis of variations in the concentration of pollutants is useful when evaluating the effectiveness of these plans. However, such an analysis cannot be undertaken using standard statistical techniques, due to the fact that concentrations of atmospheric pollutants often exhibit a lack of normality and are autocorrelated. On the other hand, if long-term trends of any pollutant’s emissions are to be detected, meteorological effects must be removed from the time series analysed, due to their strong masking effects. Materials and Methods The application of statistical methods to analyse temporal variations is illustrated using monthly carbon monoxide (CO) concentrations observed at an urban site. The sampling site is located at a street intersection in central Valencia (Spain) with a high traffic density. Valencia is the third largest city in Spain. It is a typical Mediterranean city in terms of its urban structure and climatology. The sampling site started operation in January 1994 and monitored CO ground level concentrations until February 2002. Its geographic coordinates are W0°22′52″ N39°28′05″ and its altitude is 11 m. Two nonparametric trend tests are applied. One of these is robust against serial correlation with regards to the false rejection rate, when observations have a strong persistence or when the sample size per month is small. A nonparametric analysis of the homogeneity of trends between seasons is also discussed. A multiple linear regression model is used with the transformed data, including the effect of meteorological variables. The method of generalized least squares is applied to estimate the model parameters to take into account the serial dependence of the residuals of this model. This study also assesses temporal changes using the Kolmogorov-Zurbenko (KZ) filter. The KZ filter has been shown to be an effective way to remove the influence of meteorological conditions on O₃ and PM to examine underlying trends. Results The nonparametric tests indicate a decreasing, significant trend in the sampled site. The application of the linear model yields a significant decrease every twelve months of 15.8% for the average monthly CO concentration. The 95% confidence interval for the trend ranges from 13.9% to 17.7%. The seasonal cycle also provides significant results. There are no differences in trends throughout the months. The percentage of CO variance explained by the linear model is 90.3%. The KZ filter separates out long, short-term and seasonal variations in the CO series. The estimated, significant, long-term trend every year results in 10.3% with this method. The 95% confidence interval ranges from 8.8% to 11.9%. This approach explains 89.9% of the CO temporal variations. Discussion The differences between the linear model and KZ filter trend estimations are due to the fact that the KZ filter performs the analysis on the smoothed data rather than the original data. In the KZ filter trend estimation, the effect of meteorological conditions has been removed. The CO short-term componentis attributable to weather and short-term fluctuations in emissions. There is a significant seasonal cycle. This component is a result of changes in the traffic, the yearly meteorological cycle and the interactions between these two factors. There are peaks during the autumn and winter months, which have more traffic density in the sampled site. There is a minimum during the month of August, reflecting the very low level of vehicle emissions which is a direct consequence of the holiday period. Conclusions The significant, decreasing trend implies to a certain extent that the urban environment in the area is improving. This trend results from changes in overall emissions, pollutant transport, climate, policy and economics. It is also due to the effect of introducing reformulated gasoline. The additives enable vehicles to burn fuel with a higher air/fuel ratio, thereby lowering the emission of CO. The KZ filter has been the most effective method to separate the CO series components and to obtain an estimate of the long-term trend due to changes in emissions, removing the effect of meteorological conditions. Recommendations and Perspectives Air quality managers and policy-makers must understand the link between climate and pollutants to select optimal pollutant reduction strategies and avoid exceeding emission directives. This paper analyses eight years of ambient CO data at a site with a high traffic density, and provides results that are useful for decision-making. The assessment of long-term changes in air pollutants to evaluate reduction strategies has to be done while taking into account meteorological variability     

MODELING SEDIMENT AND PHOSPHORUS LOSSES IN AN AGRICULTURAL WATERSHED TO MEET TMDLs1

ABSTRACT: This paper studies the effectiveness of alternative farm management strategies at improving water quality to meet Total Maximum Daily Loads (TMDLs) in agricultural watersheds. A spatial process model was calibrated using monthly flow, sediment, and phosphorus (P) losses (1994 to 1996) from Sand Creek watershed in south‐central Minnesota. Statistical evaluation of predicted and observed data gave r² coefficients of 0.75, 0.69, and 0.49 for flow (average 4.1 m³/s), sediment load (average 0.44 ton/ha), and phosphorus load (average 0.97 kg/ha), respectively. The calibrated model was used to evaluate the effects of conservation tillage, conversion of crop land to pasture, and changes in phosphorus fertilizer application rate on pollutant loads. TMDLs were developed for sediment and P losses based on existing water quality standards and guidelines. Observed annual sediment and P losses exceeded these TMDLs by 59 percent and 83 percent, respectively. A combination of increased conservation tillage, reduced application rates of phosphorus fertilizer, and conversion of crop land to pasture could reduce sediment and phosphorus loads by 23 percent and 20 percent of existing loads, respectively. These reductions are much less than needed to meet TMDLs, suggesting that control of sediment using buffer strips and control of point sources of phosphorus are needed for the remaining reductions.     

华北高产农区公众对农业面源污染的环境保护意识及支付意愿调查

应用假设市场价值评估法(CVM)调查了华北高产农业区桓台县公众对防治农业面源污染地下水所需费用的支付意愿;评价了公众对技术、经济、政策等解决手段的期望和行为选择。调查表明,有60%以上的公众表现出能够为后代人着想而保护农业环境的可持续发展意识,有76%的人对污染现状的改善和治理持积极态度,人均支付意愿为22.8元·a-1,但公众对农业面源污染的环境保护意识不足。影响农民公众支付意愿的因素主要有家庭收入、受教育程度和职业。经推算,该县公众1a总支付意愿大约是1114.8～1320.2万元。可采取的环境保护技术措施以改良耕作习惯、控制化肥施用量为主,法制化的环保手段需要与公众环保意识相适应。     

Sorption of polar and nonpolar aromatic compounds to four surface soils of eastern China

Improved predictions on the fate of organic pollutants in surface environments require a better understanding of the underlying sorption mechanisms that control their uptake by soils. In this study, we monitored sorption of nine aromatic compounds with varying physicochemical properties (hydrophobicity, electron-donor/acceptor ability and polarity), including two polycyclic aromatic hydrocarbons, two chlorobenzenes, two nitroaromatic compounds, dichlobenil, carbaryl and 2,4-dichlorophenol in aqueous suspension of four surface soils of eastern China. The tested soils were characterized with respect to organic carbon (OC) content, black carbon content, mineralogy, morphology and size fraction to assess the role of the diverse soil characteristics in sorption. The results of this study show that not only the solute hydrophobicity and the OC content of soil are important to the retention of organic pollutants, but also the solute molecular structure and the soil nature.     

青岛海洋环境碳纤维复合材料与低合金钢电偶腐蚀研究

目的 探究碳纤维复合材料在舰船应用时与金属材料的电偶腐蚀问题。方法 针对一种典型舰船用碳纤维增强乙烯基树脂复合材料,在青岛海洋大气环境下开展0.5、1、1.5、2 a期的自然曝晒试验,进而采用电化学分析手段考察其与低合金钢的电偶腐蚀效应,结合老化机制探究碳纤维复合材料的老化行为对其与钢电偶腐蚀的影响。结果及结论 在青岛大气环境曝晒不同周期的复合材料试样,开路电位与低合金钢相差较大,存在较高的电偶腐蚀倾向。随曝晒时间的延长,复合材料表面微裂纹不断产生、扩展,导致电化学反应活性点增多,两者电偶电流密度随之增大。在青岛海洋大气环境下暴露2 a后,碳纤维增强乙烯基树脂复合材料与低合金钢的电偶电流为0.356 9 μA/cm²,两者的电偶腐蚀敏感性达到B级。     

沈阳市地铁疏干水的利用探析

针对沈阳市地铁疏干水利用的现状,综合考虑沈阳市的实际情况,总结出地铁疏干水利用的几种方法,主要包括作为运河、湖泊的补换水源,用于修复、重建湿地,农业灌溉用水以及作为水源热泵的水源等。提出沈阳市地铁疏干水利用的指导思想和法律保障。     

大伙房水库上游地区农业面源污染现状及防治措施

通过对大伙房水库上游地区农业面源污染现状的调查研究,提出减轻农业面源污染的具体防治措施,即采用培育生物天敌、控制农药使用量、水田改为旱田和控制灌溉水的方法控制氮磷流失,从而保护水源地生态环境。     

我国水源污染事故风险点定量识别方法

水源事故的频发会对城市供水系统产生威胁,有必要针对供水系统风险进行评估和防控。针对水源事故频发及高发因素定量甄别研究,筛选统计了国内近20年来1 900多起水质突发事故案例,梳理了触发水源水质污染的多种因素,通过构建水源水质安全事故树和贝叶斯网络进行了相互验证分析。结果表明：我国水源污染事故主要因素贡献为依次突然排放(0.466)、污染长期累积(0.242)、交通事故(0.109)等;采用贝叶斯网络计算进行验证,其结果与事故树方法一致性较好。该方法有助于水源污染防控工作中风险点甄别和排序,可为我国饮用水安全保障水平的提升提供支撑。     

脱硫脱硫弧菌转化二氧化硫气体的研究

运用连续处理工艺研究了SO_2进气摩尔流速和去除率的关系,并对主要转化产物硫化氢和硫化物进行了测定,研究了亚硫酸盐的积累情况及其对脱硫脱硫弧菌生长的影响,同时还对碳源的消耗及转化产物进行了定量研究.实验结果表明,随着SO_2流速的提高(4·975~20·149mmol·h~(-1))菌体对二氧化硫的去除率没有发生明显的变化,始终保持在93%以上,在SO2摩尔流速低于5·034mmol·h~(-1)时产物以硫化氢为主,而随着SO_2摩尔流速的提高,液相中硫化物和亚硫酸盐开始累积;当SO_2摩尔流速增大至20·149mmol·h~(-1)时,亚硫酸盐累积浓度达到74·23mg·L~(-1),该浓度对菌体生长不会产生抑制作用;系统在SO_2摩尔流速为14·063mmol·h~(-1)下运行时较为稳定,乳酸盐全部转化为乙酸盐,每还原1mmol SO_2消耗0·4mmol CH_3CHOHCOO~-.     

加气站压缩机间气体爆炸数值模拟研究

加气站压缩机间安全设计时,需要评估内部气体爆炸危害,确定爆炸能量和影响因素。采用CFD技术,建立加气站压缩机间三维模型,模拟不同点火源位置、泄压板不同泄压压力和重量下,压缩机间气体爆炸时的爆炸压力及火焰传播行为。结果表明点火源位置以及泄压参数是影响加气站压缩机间气体爆炸的重要因素;点火源位置距离压缩机间放空位置越近,爆炸压力越小;对于泄压参数,爆炸压力与泄压板开启压力和重量之间均为正比关系。为减缓压缩机间内的气体爆炸危害,需要合理布置点火源位置,选择容重轻、泄压压力小的泄压材料,并同时需要考虑爆炸导致的物体破碎危害以及火焰次生灾害。