ISO 9359:1989 空気の質 — 周囲の空気の質を評価するための層化抽出法 | ページ 2

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

Draft International Standards adopted by the technical committees are circulated to the member bodies for approval before their acceptance as International Standards by the ISO Council. They are approved in accordance with ISO procedures requiring at least 75 % approval by the member bodies voting.

International Standard ISO 9359 was prepared by Technical Committee ISO/TC 146, Air quality.

Annexes A, B and C of this International Standard are for information only.

Introduction

The ambient air quality at a particular location or region is generally variable with time, this variation being caused by a number of factors, especially meteorological conditions, topography and patterns of emissions.

Such circumstances may require that a large number of measurements be made over a long interval of time to ensure that a sufficiently wide range of conditions is covered. Stratified sampling is one method which reduces the number of measurements needed to assess certain aspects of ambient air quality. This technique has been applied for example in ambient air quality surveys and in noise surveys^[1] (see examples given in annex B).

The basic aim of stratification and stratified sampling is to reduce the number of measurements needed to obtain results with a desired precision, or to improve the precision of the results without increasing the number of measurements.

To do this, information is necessary on the conditions which are likely to give rise to high, low or intermediate values of the ambient air quality characteristic of interest in the area being studied. This information is used to introduce a stratified sampling scheme in which the total number of measurements made is distributed among the different strata in such a way that the variance of the data obtained, within a given stratum, is reduced compared with the overall variance.

The reliability of the stratification scheme selected will depend upon the extent and validity of a priori knowledge, covering emission sources and the influences of topography and meteorological conditions on atmospheric dispersion. The use of results from previous measurement surveys or from specially mounted pilot surveys can be extremely helpful in the choice of strata^[2], as can the application of ambient air quality models. Data from existing ambient air quality monitoring stations which are sited to be representative of the area under examination can be used in the method.

The main body of this International Standard outlines principles to be applied for obtaining a meaningful stratification scheme. Annex A outlines the method to be used for carrying out the calculations.

1 Scope

This International Standard specifies a method for the assessment of certain aspects of ambient air quality in terms of percentiles and means using the principle of stratified sampling.

This is by estimating percentiles and means of the frequency distribution of measurements of ambient air quality characteristics. The application to the estimation of means, however, is restricted to cases where certain assumptions about the frequency distribution of the ambient air quality characteristic can be made using a priori knowledge or when a sufficient number of statistically independent measurements are available (see ISO 2854 and ISO 2602).

The results may be used to assess ambient air quality during the period of the measurement survey. (For length of period see also ISO 7168.) By using information on the longer-term occurrence of the various strata, an assessment for a longer period can be obtained using the same database.

Thus, although meteorological conditions have a profound effect on the concentration and distribution of air pollutants, stratified sampling enables results which are independent of the actual meteorological conditions prevailing during the interval of time of measurement to be calculated for a longer term.

2 Normative references

The following standards contain provisions which, through reference in this text, constitute provisions of this International Standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this International Standard are encouraged

to investigate the possibility of applying the most recent editions of the standards listed below. Members of IEC and ISO maintain registers of currently valid International Standards.

3 Definitions

For the purposes of this International Standard, the following definitions apply.

Annex C

Bibliography