ISO INTERNATIONAL STANDARD 9359 First edition 1989-09-15 Air quality - Stratified sampling method Qualite de I'air - E EchantillonnagestratifiepourI'estimationdelaqualite de Iair ambiant Reference number ISO 9359 :1989 (E) Copyright International Organization for Standardization ded by IH e with ted without license from IHS Not for Resale ISO9359 : 1989 (E) Foreword IsO(the International OrganizationforStandardization)isaworldwidefederationof national standards bodies (iso member bodies). The work of preparing International Standards is normally carried out through Iso technical committees. Each member bodyinterested inasubjectforwhichatechnical committeehasbeenestablishedhas the right to be represented on that committee. International organizations, govern- mental 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 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 ISO 1989 Allrights reserved. No part of this publication may be reproduced or utilized in any form or by any means, electronic or mechanical, including photocopying and microfilm, without permission in writing from the publisher. International Organization for Standardization Case postale 56 . CH-1211 Geneve 20 . Switzerland Printed in Switzerland ii Copyright ional Organization for Standardization rovided by IHS under license with IS Not for Resale ISO·9359:1989 (E) 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 con- ditions,topographyandpatternsof 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 [11 (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 dif- ferent 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 stratificationscheme 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 helpfut in the choice of strata (21, as can the application of ambient air 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 Not for Resale