# ISO 9359-1989

MS ISO 93592009 AIR QUALITY - STRATIFIED SAMPLING FOR ASSESSMENT OF AMBIENT AIR QUALITY ISO 9359 1989, IDTISO 93591989 is endorsed as Malaysian Standard with the reference number MS ISO 93592009. ICS 13.040.20 Descriptors air, quality, sampling Copyright 2009 DEPARTMENT OF STANDARDS MALAYSIAMALAYSIAN STANDARD DEVELOPMENT OF MALAYSIAN STANDARDS The Department of Standards Malaysia STANDARDS MALAYSIA is the national standardisation and accreditation body. The main function of the Department is to foster and promote standards, standardisation and accreditation as a means of advancing the national economy, promoting industrial efficiency and development, benefiting the health and safety of the public, protecting the consumers, facilitating domestic and international trade and furthering international cooperation in relation to standards and standardisation. Malaysian Standards are developed through consensus by committees which comprise of balanced representation of producers, users, consumers and others with relevant interests, as may be appropriate to the subject in hand. To the greatest extent possible, Malaysian Standards are aligned to or are adoption of international standards. Approval of a standard as a Malaysian Standard is governed by the Standards of Malaysia Act 1996 Act 549. Malaysian Standards are reviewed periodically. The use of Malaysian Standards is voluntary except in so far as they are made mandatory by regulatory authorities by means of regulations, local by-laws or any other similar ways. The Department of Standards appoints SIRIM Berhad as the agent to develop Malaysian Standards. The Department also appoints SIRIM Berhad as the agent for distribution and sale of Malaysian Standards. For further ination on Malaysian Standards, please contact Department of Standards Malaysia OR SIRIM Berhad Century Square, Level 1 b the comma which is used as a decimal sign if any, to read as a point; c Clause/Subclause Modifications 5.1 Examples 1 To read the example as “Airborne particulate emission may vary considerably depending on weather patterns in Malaysia with seasonal occurrence of “haze” during dry periods of the year, which normally disappears with the onset of the rainy season.” Explanation To justify with Malaysian climate. d reference to International Standards should be replaced by equivalent Malaysian Standards as follows Referenced International Standards Corresponding Malaysian Standards ISO 2602, Statistical interpretation of test results - Estimation of the mean -Confidence interval MS ISO 2602, Statistical interpretation of test results - Estimation of the mean -Confidence interval ISO 2854, Statistical interpretation of data -Techniques of estimation and test relating to means and variances MS ISO 2854, Statistical interpretation of data - Techniques of estimation and test relating to means and variances ISO 3534, Statistics - Vocabulary and symbols MS ISO 3534 all parts, Vocabulary and symbols Compliance with a Malaysian Standard does not of itself confer immunity from legal obligations. NOTE. IDT on the front cover indicates an identical standard i.e. a standard where the technical content, structure, wording or is an identical translation of a Malaysian Standard is exactly the same as in an International Standard or is identical in technical content and structure although it may contain the minimal editorial changes specified in clause 4.2 of ISO/IEC Guide 21-1. INTERNATIONAL STANDARD IS0 9359 First edition x389-09-15 Air quality - Stratified sampling for assessment of ambient air quality Qualit de l/air - khan tillonnage s tra tifih pour /es tima tion de la qualit de lair ambiant Reference number IS0 9359 1989 El IS0 9359 1989 El Foreword IS0 the International Organization for Standardization is a worldwide federation of national standards bodies IS0 member bodies. The work of preparing International Standards is normally carried out through IS0 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, govern- mental and non-governmental, in liaison with ISO, also take part in the work. IS0 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 IS0 Council. They are approved in accordance with IS0 procedures requiring at least 75 approval by the member bodies voting. International Standard IS0 9359 was prepared by Technical Committee ISO/TC 146, Air quality. Anns A, B and C of this International Standard are for ination only. 0 IS0 1989 All rights reserved. No part of this publication may be reproduced or utilized in any 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 l CH-121 1 Geneve 20 l Switzerland Printed in Switzerland ii IS0 9359 1989 El 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, 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 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 survey quantile The value XP which separates the range of the population of a parameter into two groups at the level of the fractionf P/100, where P is a given percentage. 3.3 stratified sampling Of a population which can be divided into different sub-populations called strata, sampling carried out in such a way that specified proportions of the sample are drawn from the different strata. ISO 35341 3.4 stratum Sub-population of a population characterized by certain features. 1 IS0 9359 1989 E 4 Symbols Symbol Meaning f weighted fraction of the values of fi f upper confidence limit for the weighted fraction f - lower confidence limit for the weighted fraction f i fraction of the ith stratum being below or above a given value k n ni mi number of strata total number of measurements number of measurements in the ith stratum number of measurements having a value below a given value in the ith stratum pi percentage of the ith stratum being below or above a given value Pi 100 fi estimate for the variance off estimate for the variance of X estimate for the variance of fi estimate for the variance of xv tabulated value of the t-distribution for the one- sided test at the significance level a and for v degrees of freedom for tables see IS0 2602 U1-CZ. tabulated value of the standardized normal distribu- tion for the one-sided test at the significance level a x X x- - xi weighted mean of the values of Xi upper confidence limit for the weighted mean lower confidence limit for the weighted mean arithmetic mean of measurements within the ith stratum j wi jth measurement in the ith stratum probability of occurrence of the ith stratum given as a weighting factor XP percentile ; fractile or quantile a significance level l-a confidence level A margin of error P mean of population Pi mean of the ith stratum V number of degrees of freedom am variance of fi their source can be considered to be linear in the case of a major road or areal in the case of an urban area. If airborne lead levels were being assessed in the vicinity of a main highway, then the strata used could be based on distance from the highway and time of day in relation to peak traffic flow periods. A spatial or temporal stratification could be used to assess carbon monoxide levels in an urban area. 5.2 Transport and dispersion When selecting criteria for a stratification scheme related to the transport and dispersion of air pollutants in the atmosphere, it is necessary to decide whether long-range transport of air pollution, governed by synoptic factors, or nearby sources, meteorological effects and topography, is the dominant in- fluence on the ambient air quality characteristic of interest. Stratification may then be based on factors such as - local topography; - air temperature; - wind speed and wind direction; - atmospheric stability; 2 - mixing height; - solar radiation; - weather type; - air mass type; or on results of dispersion models. These models using emission and meteorological data predict the temporal and spatial pattern of ambient air quality which may be used to devise stratification schemes. EXAMPLES I Considering the effects of a single emission source at some distance from the area under examination, a stratification based on wind speed and wind direction may be useful see also clause B. I . 2 An assessment of ambient air quality may be required in an urban-industrial basin area with many emission sources. Here, a variety of parameters could be examined for their suitability, e.g. atmospheric stability, seasonal effects, wind speed and wind direction see also clause B.2. 3 If concentrations of carbon monoxide need to be assessed at street level in an area with tall buildings, e.g. in the central part of a large city, then wind speed and wind direction may be used along with the time of day see also 5. I, example 1. 4 If oxidants are being assessed, a stratification based on solar radiation, wind direction and temperature may be useful. 5 For inter-regional or long-range transported air pollutants, the air mass concept may be used. 5.3 Associations with other ambient air pollutants Some ambient air quality characteristics are indicative of at- mospheric conditions or are associated with other ambient air quality characteristics of interest. The concentrations of certain ambient air pollutants may be closely correlated and stratified sampling for the ambient air pollutant of interest may then be carried out on the basis of the level of the indicator ambient air pollutant. EXAMPLE - The concentrations of the ambient air pollutant of interest, as measured for example at a fixed, continuous monitoring station, can be used to define strata within which random sampling can be pered see also clause B.3. 5.4 Effects The effects of ambient air pollution may lend themselves to establish a stratification. EXAMPLES I Effects on plant growth or crops could lead to an areal or temporal stratification. 2 Frequency and occurrence of complaints from the public about odours, for example, could also be used. 3 Plants and growth periods. IS0 9359 1989 El 5.5 Pilot surveys If it is not possible to devise a stratification on the basis of existing knowledge of ambient air quality and the factors governing its variation in the area of interest, then it may be necessary to set up a pilot survey of ambient air quality, or to carry out calculations using ambient air quality models, which are themselves based on stratification. 5.6 Ambient air quality models Ambient air quality models, using emission and meteorological data to predict the temporal and spatial emission patterns of ambient air quality, may be used to devise stratification. 61 . Measurement guidelines Number of strata and number of measurements per stratum Having decided on a stratification criterion, it is then necessary to decide how many strata are to be used, and how many measurements are to be made within each stratum to achieve a desired confidence limit in the assessment. Experience with the stratified sampling technique has shown that the reduction in variance obtained by increasing the number of strata, k, soon falls off, and that k 2, 3, or 4 is usually sufficient. If the probability, Wj, and the estimate of the variance of each stratum, sf, are known from a priori knowledge see 5.1 to 5.4 or a pilot survery see 5.51, the total number of measurements, n, for a given margin of error, A, is given by equation I I The theory of stratified sampling shows that, once the total number of measurements to be made has been decided upon, it is possible to allocate these among the different strata so as to achieve a minimum variance in the results calculated for the population. If the arithmetic mean is cation is achieved when li l . . . k c Wi Si il Wj Sj determined, then this optimum allo- And if fractions are determined, then Wj dfi 1 - fi ni n k c wi l/fi 1 - fi 2 . . . 3 3 IS0 9359 1989 El In other words, a large number of measurements should be car- ried out in a particular stratum if that stratum has a higher prob- ability of occurrence, as given by Wit or a large variance, as given by S; or fi 1 - fi s To calculate the number of measurements in the ith stratum, ni, precisely, knowledge of both Wi and cti or fi is needed. While the weighting factors, Wit may be established before the measurements begin, it is likely that there is little or no infor- mation on ai or ji, Consequently, it is advisable to refine ni as the measurements proceed, by calculating Si orfi and then making use of these in equations 2 or 3. NOTE - The validity of some of the equations given in annex A will depend upon the number of measurements made in a particular stratum. Thus equation A.9 requires that ni 15 since it is based on the approximated binomial test ; if this is not satisfied, then exact theory must be used. The equation giving confidence limits for the weighted mean equation A.lO is always valid if ni 5. ni may be less if the frequency distribution of the air quality characteristic in the ith stratum is gaussian. In cases where ination about the va tional allocation to Wi may be suitable. riance is not available, propor- 62 . Independence of measurements In order to apply the equations and s of calculation specified in this International Standard, it is necessary for the measurements to be carried out in a manner such that they may be assumed to be independent. NOTE - Ambient air quality measurements at a particular measure- ment site are often highly auto-correlated and it may thus be necessary to ensure intervals of time of sufficient length between the measure- ments. For example, strong auto-correlations have been observed in central Europe for periods up to six days. When stratified sampling is employed, independent measured values could well be obtained at shorter intervals of time, because correlation effects due to changes from one stratum to another have been eliminated. 63 . Interval of time and site of measurements Having established