How many samples are required? Evaluating a model for verification of carbon sequestration in a hybrid poplar buffer strip

A model is developed to predict annual and total above-ground carbon storage within a hybrid poplar stream buffer. The regression model predicts tree wet weight based upon circumference at breast-height (137 cm) with an r-square value of 0.9922. Carbon storage in above-ground biomass is estimated to be 3.57 to 3.71 metric tons per hectare, with a measured annual increment of 0.92 to 1.37 metric ton per hectare per year. The variability of carbon storage within this biological system, including soil organic matter, is explored, and the number of samples required to achieve a desired level of statistical certainty are predicted. As has been investigated previously for other biological systems (Garten and Wullschleger, 1999), the study shows that a prohibitively large number of samples must be taken in order to achieve high degrees of certainty about mean carbon storage values. The study also shows, however, that mean values with somewhat greater uncertainties can easily be achieved with much smaller sample sizes. Thus carbon sequestration verification might be accomplished cost-effectively if the degree of certainty required is not unrealistically high for highly variable natural systems.     

无除湿预处理采样法测定烟气中低浓度SO2

针对海水脱硫后的烟气具有SO2浓度低、湿度大、温度低的特点，提出了在烟道内无需除湿预处理的直接采样测定SO2的方法，解决了国标法进行除湿采样或使用较先进仪器直接脱水测定带来的测定结果偏低问题。实际应用表明，谊法比在烟道外使用的除湿法更加准确、经济。     

Graphical effluent quality control for compliance monitoring: What is a violation?

Demonstration of compliance with discharge (effluent) requirements suffers because Discharge Monitoring Reports (DMRs) give neither the discharger nor the regulator information on the process mean which ensures compliance. To obtain this information, a simple graphical method is presented which takes into account process variability. This technique provides quality control specifications for the monitoring data and the process itself.     

Sampling of airborne polycyclic aromatic hydrocarbons with semipermeable membrane devices

Semipermeable membrane devices (SPMDs) are nowadays used as passive samplers of organic pollutants. The knowledge of the sampling rate values (R_S) of each substance trapped on membranes is necessary to calculate their average concentration. Here we calculate R_S values for 16 polycyclic aromatic hydrocarbons using the comparison of active sampling method results and the amounts sequestered by SPMDs at varying exposure times.Selected article from the Regional Symposium on Chemistry and Environment, Krusevac, Serbia, June 2003, organized by Dr. Branimir Jovancicevic.     

大气扩散参数的取样时间订正

就大气环境影响评价浓度预测中 ,对大气扩散参数取样时间订正问题进行了说明和讨论。     

全氟二甲基环丁烷示踪剂吸附采样

借助气相色谱基本原理,测定了全氟二甲基环丁烷大气示踪剂通过Carboxen-569碳分子筛吸附管的分配系数,考察了温度和采样速度对穿透体积和安全采样体积的影响,确定了示踪剂吸附采样的基本参数吸附剂用量为150mg,吸附采样温度≤40℃,采样速度为200mL/min,样品解吸温度为200℃.     

Diffusive gradients in thin films (DGT) probe for effectively sampling of per- and polyfluoroalkyl substances in waters and sediments

The passive sampling technique, diffusive gradients in thin films (DGT) has attracted increasing interests as an in-situ sampler for organic contaminants including per- and polyfluoroalkyl substances (PFAS). However, its effectiveness has been questioned because of the small effective sampling area (3.1 cm²). In this study, we developed a DGT probe for rapid sampling of eight PFAS in waters and applied it to a water-sediment system. It has a much larger sampling area (27 cm²) and as a result lower method quantification limits (0.15 – 0.21 ng/L for one-day deployment and 0.02 – 0.03 ng/L for one-week deployment) and much higher (by > 10 factors) sampling rate (100 mL/day) compared to the standard DGT (piston configuration). The sampler could linearly accumulate PFAS from wastewater, was sensitive enough even for a 24 hr deployment with performance comparable to grab sampling (500 mL). The DGT probe provided homogeneous sampling performance along the large exposure area. The use of the probe to investigate distributions of dissolved PFAS around the sediment-water interface was demonstrated. This work, for the first time, demonstrated that the DGT probe is a promising monitoring tool for trace levels of PFAS and a research tool for studying their distribution, migration, and fate in aquatic environments including the sediment-water interface.     

Evaluation of offline sampling for atmospheric C3-C11 non-methane hydrocarbons

The concentration variation of C3-C11 non-methane hydrocarbons(NMHCs) collected in several types of commercial flexible bags and adsorption tubes was systematically investigated using a gas chromatography-flame ionization detector(GC-FID) system. The percentage loss of each NMHC in the polyvinyl fluoride(PVF) bags was less than 5% during a 7-hr storage period; significant NMHCs loss was detected in aluminum foil composite film and fluorinated ethylene propylene bags. The thermal desorption effic...