经合组织的可持续农业思路

经合组织为其29个成员国提供了一个论坛,来讨论以经济分析和共享各国经验为基础的经济政策与社会政策,以期向各国政府提供政策忠告和建议.近年来,已经更多地注意到经合组织国家与非经合组织国家之间的彼此相互作用,在市场、贸易和投资的全球化与自由化范畴内尤其如此. 　　目前,正在进行一个关于可持续发展的重大经合组织项目,利用经合组织中范围广泛的社会经济人才,准备2001年向经合组织部长会议的报告,并作为对2002年“里约+10”联合国会议的投入.在考察到底发生了什么的基础上,旨在概述提请政策制定者努力保持和加强可持续发展的方式——覆盖经济方面、环境方面和社会方面.1999年向经合组织部长会议的中期报告可上网浏览：www.oecd.org/subject/sustdev.......     

Variation of Solar Attenuation with Height over an Urbanized Area

The information presented in this paper is directed to environmental scientists who are concerned about the quality of air over an urban area. Specifically, the purpose of this study is to show quantitatively the magnitude of solar attenuation for individual air layers in the lowest 1000 m of an urban atmosphere. This reveals dramatically the diverse variation of mass concentration with height. The information is useful in urban planning, in site selection, and in air quality control.

The data were gathered on different roof top levels and on helicopter flights using modified Volz sun photometers, psychrometers, hot-wire anemometers, and an electric thermometer. The results show that, for instance, on a "polluted" day the lowest 1000 m of air attenuate about 65% of the solar beam, whereas on a “clean” day the contribution to the total solar attenuation is still 30%. Shallow air layer increments of 45 m near the ground were found to contribute up to 21% to the total solar attenuation. Aerosols form the dominant attenuation component in polluted air layers near the ground, whereas the extinction due to air molecules becomes dominant in higher and relatively cleaner atmospheric air layers.

Significance tests show that turbidity variations with height over widely spaced locations are relatively homogeneous. This may indicate a rather uniform spread of the urban dust dome over the neighboring countryside. No significant change in the vertical turbidity structure was found between data collected in 1961–62 and 1969.

For an effective control of the ambient air quality, conclusive information on the lateral and vertical spread of pollution is necessary. Turbidimetric studies based on scattering theory can economically supply this information.     

经合组织的可持续农业思路

经合组织为其29个成员国提供了一个论坛,来讨论以经济分析和共享各国经验为基础的经济政策与社会政策,以期向各国政府提供政策忠告和建议.近年来,已经更多地注意到经合组织国家与非经合组织国家之间的彼此相互作用,在市场、贸易和投资的全球化与自由化范畴内尤其如此.     

The socioeconomic significance of nature-based recreation in Canada

In recognition of the many values that people ascribe to nature, federal, provincial, and territorial agencies worked inpartnership to complete the 'Survey on the Importance of Natureto Canadians' (SINC) in 1981, 1987, 1991, and 1996. Between 1981 and 1996, more than 80% of Canadians 15 years of age and older engaged in one or more nature-related activities. This paper describes the evolution of this cooperative monitoring program, defines a classification system as a context for the values examined by the SINC, highlights trends of some nature-related recreational activities measured by the survey, and comments onthe importance of this information to Canadians.     

The use of sensor arrays for environmental monitoring: interests and limitations

Continuous, in situ monitoring of air, water and land quality is fundamental to most environmental applications. Low cost and non-invasive chemical sensor arrays provide a suitable technique for in situ monitoring. Their ability and performance under realistic conditions is discussed in this paper. Published studies report promising results despite a number of limitations that are associated with both the technology itself and its application in ever changing ambient conditions. Early investigations include the analysis of single substances as well as odour and wastewater organic load monitoring. Reported applications typically highlight the sensitivity of the currently available sensors to changes in temperature, humidity and flow rate. Two types of approaches are recommended to deal with these effects: either working under fixed experimental conditions or measuring the external parameters to numerically compensate for their change. The main challenge associated with the use of non-specific sensor arrays lies in establishing a relationship between the measured multivariate signals and the standards metrics that are traditionally used for quality assessment of gas mixtures. For instance, odour monitoring requires calibration against olfactometric measurements while investigations of wastewater samples still need to be correlated with organic pollution parameters such as BOD, COD or TOC. On the other hand, results obtained in the field have demonstrated how sensor arrays can be readily used as simple alarm devices or as early warning systems based on a general air/water quality index.