Determination of Nitrogen Oxides in Auto Exhaust

A new procedure for determining nitrogen oxides in automobile exhaust has been developed. The new procedure was included in a Bureau of Mines comparative study that aimed at evaluating various widely used methods for determining NO_x in auto exhaust. The methods included in the evaluation study follow: (1) Static oxidation in tank (ST method). The method involves oxidation of NO in residence with O₂ in a stainless steel tank. (2) Bureau of Mines method (BM method). The method involves application of the ST procedure in exhaust samples from which the hydrocarbons have been removed by combustion over catalyst. (3) Chevron Research method (CR method), as described in the literature. (4) Phenoldisulfonic acid method (PDS method), as described in the literature. The principal objective of this study was to generate experimental evidence which would lead to defining an optimum procedure for converting NO, present in exhaust gas, into NO₂; this conversion is desired so that the total of NO + NO₂ can be determined quantitatively in the form of NO₂. In pursuing this objective, the procedures prescribed by the foregoing methods were comparatively tested. The results indicated that all four methods are subject to error, the extent of which depends on the conditions employed. The BM method was superior from the standpoint of accuracy because it was less affected by interferences due to hydrocarbon-NO₂ reactions.     

Using continuous PM2.5 monitoring data to report an air quality index

As stated in 40 CFR 58, Appendix G (2000), statistical linear regression models can be applied to relate PM2.5 continuous monitoring (CM) measurements with federal reference method (FRM) measurements, collocated or otherwise, for the purpose of reporting the air quality index (AQI). The CM measurements can then be transformed via the model to remove any bias relative to FRM measurements. The resulting FRM-like modeled measurements may be used to provide more timely reporting of a metropolitan statistical area's (MSA's) AQI. Of considerable importance is the quality of the model used to relate the CM and FRM measurements. The use of a poor model could result in misleading AQI reporting in the form of incorrectly claiming either good or bad air quality. This paper describes a measure of adequacy for deciding whether a statistical linear regression model that relates FRM and continuous PM2.5 measurements is sufficient for use in AQI reporting. The approach is the U.S. Environmental Protection Agency's (EPA's) data quality objectives (DQO) process, a seven-step strategic planning approach to determine the most appropriate data type, quality, quantity, and synthesis for a given activity. The chosen measure of model adequacy is r2, the square of the correlation coefficient between FRM measurements and their modeled counterparts. The paper concludes by developing regression models that meet this desired level of adequacy for the MSAs of Greensboro/Winston-Salem/High Point, NC; and Davenport/Moline/Rock Island, IA/IL. In both cases, a log transformation of the data appeared most appropriate. For the data from the Greensboro/Winston-Salem/High Point MSA, a simple linear regression model of the FRM and CM measurements had an r2 of 0.96, based on 227 paired observations. For the data from the Davenport/Moline/Rock Island MSA, due to seasonal differences between CM and FRM measurements, the simple linear regression model had to be expanded to include a temperature dependency, resulting in an r2 of 0.86, based on 214 paired observations.     

Summertime measurements of benzene and toluene in Athens using a differential optical absorption spectroscopy system

In this paper, measurements of benzene, toluene, p,m-xylene, ozone (O3), nitrogen dioxide (NO2), and sulfur dioxide (SO2) made using the differential optical absorption spectroscopy (DOAS) technique during a 4-month period of summer 2000 (June-September) in Athens, Greece, are presented. An assessment of benzene mean value concentrations during this 4-month period exceeded 10 microg/m3, which is 2 times greater than the average yearly limit proposed by European authorities. Toluene measurements present mean values of approximately 33 microg/m3. Benzene and especially toluene measurements are highly correlated with NO2 and anticorrelated with O3. High values of benzene, NO2, and toluene are also correlated with winds from the southeast section, an area of industrial activity where emissions of volatile organic compounds (VOCs) have been recorded in previous studies. O3 is correlated with winds from the south-southwest section affected by the sea breeze circulation. Diurnal variations of O3, NO2, and SO2 concentrations are compatible with measurements from the stations of the Ministry of Environment's network. Outliers are combined with weak winds from the south-southwest. As far as p,m-xylene measurements are concerned, there is a poor correlation between gas chromatography (GC) and DOAS Opsis measurements, also observed in previous relevant campaigns and eventually a criticism in the use of the DOAS Opsis model for the measurement of p,m-xylene.     

地下水过量开采的概率风险分析

应用一种概率风险分析方法评价了济宁市地下水水位降落漏斗区的风险度。该方法引入了可靠度和严重度来进行分析评价，可靠度从宏观上反映了含水层系统的安全可靠程度，而严重度从微观上详细地刻画了含水层系统的易破坏程度。其中，影响可靠度大小的因子主要有可开采量和实际开采量，严重度大小的主要影响因子包括实际开采量、净补给、降深和含水层的初始饱和厚度。在可靠度和严重度计算结果的基础上，利用AreGIS软件计算了漏斗区风险度的空间分布。结果表明：占研究区总面积5．53％的中部地区风险度最大，而西部和南部的风险度相对很小，符合该地区实际的水文地质条件和地下水资源的开采现状。