Urban air pollution worldwide Results of the GEMS air monitoring project
Burton G. Bennett Monitoring and Assessment Research Centre Chelsea College University of London London SWlO OQX, U.K.
Jan G . Kretzschmar Study Centrefor Nuclear Energy Mol, Belgium Gerald G . Akland Environmental Protection Agency Research Triangle Park, N. C. 27711 Henk W. de Kooing World Health Organization Geneva. Switzerland A global program of air quality monitoring was established by the World Health Organization (WHO) in 1973. Its objectives are to assist countries in operational air pollution monitoring, to improve the practical use of data in relation to the protection of human health, and to promote the exchange of information. During the initial phase of the project, 14 countries participated, supplying data on sulfur dioxide ( S a ) and suspended particulate matter (SPM) from selected sites of their national networks. In each country information was routinely collected from three sites of primarily industrial, commercial, and residential character of a major UTban area. In 1976, the air monitoring project k a m e a part of the Global Environment Monitoring System (GEMS). Financial support provided since then by the United Nations Environment Programme (UNEP) has been used to extend the network into developing countries and to continue efforts to improve monitoring methods and procedures. In 1976, the World Meteorological Organization became a cooperating agency 298 Environ. Sci. Technol.. Vol. 19, NO.4, I985
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in the project and has assisted in preparing guidelines and in organizing training workshops to demonstrate measurement techniques and to consider network design and data analysis. The results of pollutant measure-
ments at the monitoring sites in the network are published in biennial data reports (1-4). Reports have been publ i e d that give details of monitoring methods (3,air monitoring program design (@, methods of analyzing and
0013-936WB5/09194298$01.50/0 0 1985 American Chemical Society
interpreting air monitoring data (3, and estimating human exposure to air pollutants (8).The first interpretive report of data collected in the network from 1973 to 1980 has been prepared and is being published (9). This paper is a summary of the report; in it we present additional analyses of the data accumulated from the networks.
GEMS network At present, some 50 countries are participating in the GEMS air monitoring project in which data are obtained at approximately 175 sites in 75 cities. Measurements have so far been limited to S a and SPM as indicators of industrial pollution in urban areas. This network encompasses a wide range of urban conditions, such as population distribution, industrial development, local topography, and clitology. The air monitoring project is exto provide a global view of au quality conditions in urban areas. The geographical coverage of the GEMS network is fairly representative of the world regions. The highly industrialized countries of the Northern Hemisphere are well represented. Most sites in the developing countries became operational after 1976, and fewer data are available from these locations. A map of the monitoring sites and a discussion of the early development of the project have been published (10). The air quality measurements are made at two or three. designated sites in every city. These are usually representative sites from national air monitoring networks. Sites have been classified as city center or suburban and further characterized as commercial, industrial, or residential. Daily average measurements of SO2 and particulate concentrations in air are made by a number of different but wellaccepted methods (5).Determinations of SO2 in the network are made by the acidimetric titration or hydrogen peroxide method (at 36% of the sites), the colorimetric pararosaniline or WestGaeke method (27%), the amperornetric or coulometric method (21%), and the conductimetric method (12%). At a few sites (4%), flame photometry or pulsed fluorescence detection is used. There are two methods primarily used for determination of SPM concentm tions: gravimetric measurement using the high-volume sampler (at 46% of the sites) and the smoke shade method (43%). The remainder of the sites use the membrane sampler (4%) or fully automated, continuously measuring nephelometry or beta absorption (7%). Because many of the sites are included in national networks, quality conwl procedures should normally be
Air is bubbled throuah 0.Wo nvdroaen oe sent fGms sulfurk acG, which is
. 'sbubbled through a dilute aqueution. SO2 is continuously abtomercurate ion, which then rerarosaniline to form red purple
current necessary to maintain a constant quantitative measure of the SO2 input. sample of about 2 m3/d is collected and
and centered near 340 nm. The fluores
SPM measurement methods
is drawn through a glass or synthetic organic fiber a motor wid blower. The filter surface is arranged horizontally, facing , and is protected by a roof and shelter enclosure that keeps out rain snow and generally prevents the collection of particles larger than about m. The air flow rates range from 1.1 m3/min to 1.7 m3/min. The concenby dividing the net weight of the particulate by olwrw anp/er-Air
is drawn through a filterpaper, forming a stain, ured with a photoelectric reflectometer. Each meter are collected in about 2 m3 of air. me s partly on the m a s of the smoke particles and sity to the weight of deposited smoke particles has been established for
part of the earlier phase of data collection. The reliability of the various methods for S@ detection has been checked in independent studies. An intenxmparison exercise for participants in the GEMS network using the reference West-Gaeke method has been completed (4). The results from 16 laboratories showed most analyses of standard samples grouped within f 2 5 % of the reference mean, with four laboratories having somewhat larger deviations. Such intercomparisons are of great value in maintaining high stan-
dards for independent sampling and analysis in large networks. Awareness of the field sampling difficulties under the varying local conditions is required. For example, with the colorimetric method for SO2, higher temperatures may affect the absorption of SO2 and the stability of the solution prior to analysis. In using the conductimetric method for SO2, precautions are necessary to eliminate or account for other substances in air which could affect the readings. Comparisons of the two main methEnviron. Sci. Twhnol., Mi. 19, No. 4, 1985 299
AirplIution has been monitored mUrinely at these sires since 1976.
ods for SPM determinations in parallel
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operation at various sites show that high-volume and smoke measurement results differ by a factor of around two or three (9).The methods depend on the physical characteristics of the particles; the high-volume determinations are based on mass measurement and the smoke method depends on the reflectivity from the fiiter stain. The specific relationship between the two methods depends on local conditions at specific sites. In the analyses of these data, sep mate distinction is made of the highvolume particulate measurements and the smoke determinations.
Data d y & The operation of the GEMS air mon- Ihe tourist's view OfBigBen and the Houses of Parlimnem. . itoring network has resulted in the acquisition of substantid amounts of data. In more recent years, 25,000 to 30,000 dailv measurements for each wllutant ha& been added each year to'the data fide. It has been convenient to summa, , . ,..;,., rize annual measurements at each site in a cumulative frequency table. The minimum and maximum daily averages am recorded along with the arilhmetic and geometric means and the standard deviations of the annual resulu (1-4). Graphical illustration of the data is useful, and for this purpose the lognor.. mal representation appears to be satisfactory. Approximately straight line plots are formed on log-probability eranh -1. esDeciallv in the ranee h m the mebian'to the'%& pemntZe values. In the majority of data s a , the lowest values are close to or even be- . . . is obliterated on a smoggy day ,
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Emimn. Sci. Technol.. MI. IS,No. 4, 198.5
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low the detection limit, so their accuracy is questionable. At the upper range of the distribution, the representativeness and accuracy of maximum values are often hard to evaluate. Errors in sampling, analysis, or reporting are frepuently involved. In some cases local and exceptional phenomena also may explain certain outliers. During the period 1973-80, 1451 sets of yearly statistics were formed from the network results, each set conor SPM concentration sisting of values at a specific site for a specific year. There are 736 sets of yearly values and 715 sets of yearly SPM values. Not all of these results are complete for entire years. Only if the daily values are relatively uniformly distributed throughout the year can representative annual values be presumed. Based on a carefulexamination of eacb yearly set of daiiy values, 74% of the Sa sets and 79%of the SPM sets were judged to be representative (9). A tabulation of all the representative yearly SO2 averages obtained in the network up to 1980 is given in Table 1, which shows the number of annual average values from all sites and the median and the range of annual averages. Because of the changing composition of the network, it is difficult to compare values from one year with the next. Over the entire eight-year period there are 541 annual average values of SO, concentration at all sites of the network with a median value of 45 pg m-3 and a range of 3-242 pg I I - ~ . Figure 1 shows the distribution of measurements for 1973 to 1980. The distribution is peaked in the lower range with long tailing out to the upper range, approximately lognormal in the same way as the daily values at individual sites. Four values from two center city sites in Milan are >200 pg I I - ~ . At the other extreme, with annual means ~5 pg I I - ~ ,although not always consistently reported year to year, are some sites in Melbourne, Kuala Lumpur, Lima, Toulouse, Hong Kong, and Houston. Most of the sites (90%) are within the range of 11-135 pg The central range for 50%of the values is 21-72 pg The results of SPM measurements in the GEMS network are given in Tables 2 and 3. For the gravimetric determinations of SPM by high-volume sampling, including the miscellaneous methods of SPM determination (nephelometry, membrane filtration, and beta absorption), there are 334 annual average values at all sites of the network from 1973 to 1980, with a median concentration of 89 pg m-3 and a range of 24547 pg m-3 (Table 2). The distribution of these measurements is some-
Sa
Sa
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what similar to that for SO2 (F-igure 1). A large number of values in the upper end of the distribution were recorded in Calcutta, Delhi, and Tehran. At the lower end of the distribution, several annual means of 200 pg m-3 reported. Most smoke values are in the lower range ( 0.7). For the remainder of sites within a given city, the results for a particular pollutant were less significantly correlated (r < 0.7). Abrupt changes in general intersite relationships can be used to draw attention to unusual local changes in source emissions or perhaps to abnormal monitoring operations. Correlations of SQ and particulate measurements at the same site also have been investigated (9). In general, when SQ levels are elevated, SPM levels also are higher. But this relationship is variable, covering a wide range of significance (from r = 0 to r > 0.9). The general seasonal cycles strongly influence the observed correlations. Details of the correlation analyses are given in the interpretive r e p r t of the GEMS data(9).
Comparisons of guidelines To l i t the effects of exposure of the general public, guidelines for So, and particulate levels in air have been suggested by WHO (11). For annual average concentrations relevant to longterm effects, the guideline values are 40-60 pg m-3 for SO2 and smoke, and 60-90 pg m-3 for gravimetrically determined particulate levels. Most sites in the GEMS network with average concentrations taken from 1975 to 1980 are below or within the guideline values. About one-quarter of the sites are above the upper guideline for A somewhat greater proportion, just over 40% of all sites, is above the upper guideline for SPM, including smoke. City center, industrial, and commercial sites are more frequently above the upper guideline and suburban residential sites are usually below the lower guideline value. For liiting acute effects from shortterm exposure to air pollutants, the guideline values applied to the 98th per-
m.
Environ. Sci. Technot.. Mi. 19,NO.4,1985 303
centile of the daily averages are 100- trends in the maximum (98th percen150 pg m-3 for SO2 and smoke and tile) values (9). 15&230 pg m-) for SPM (high-volThe causes of these trends can be inume determination). The upper guide- vestigated only with additional inforlines are exceeded by nearly one-third mation from the local areas. Upward of all sites for SO2 and by nearly one- trends may be due to increased indushalf of the sites for SPM. Residential trial activity or urban expansion. Gensites are more frequently below the erally, lower urban air pollutant levels guideline values than are commercial are attributed to emission reduction systems, use of low-sulfur fuel, fuel conor industrial sites. Further comparisons of the monitor- servation policies, and high stacks to ing results with regional or national air increase dispersion. quality standards may be made. These are best accomplished by the local in- Conclusion The wide participation of countries in vestigator with the specific and relevant regulatory limits. Examples of such the GEMS air monitoring project enstandards are the European Community sures that representative distributions Directive (12) and the U S . National of the levels of SOz and SPM are obAmbient Air Quality Standards (13). tained for urban areas. This global picre of urban air pollution gives useful The air concentrations of SO2 and SPM or smoke in these standards are approx- perspective in considering the results imately comparable to the upper values from any one monitoring site. The wide range of pollutant levels in of the WHO-suggested guidelines. the network reflects the wide range of Air quality trends local conditions. Individual sites someThe determination of trends in urban times show relatively high levels of SO, air quality is an important objective of or SPM and comparisons with the the air monitoring project. Because of WHO guidelines show that improvethe changing composition of the net- ment is still needed to reduce annual work, it has been possible to look at average levels and peak daily concentrends only at the individual sites. The trations. Although the majority of sites major limitation of the trend analysis is in the trend analysis show downward or that the period is still quite short, up to stationary trends, upward trends were noted at IO of 63 sites for SO2 and at 6 eight years. A semiquantitative procedure has of 62 sites for SPM. These results of the first interpretive been used for the trend analysis. Comparisons are made in the changes in av- analysis of the GEMS network data erage levels from the first half of the form an initial survey of urban air qualmonitoring period to the second half. ity conditions throughout the world. For classification purposes the trend is Additional periods of monitoring will said to be downward if the change is at improve the representativeness of the least -3% per year. An upward trend results and strengthen the trend analysis requires at least +3% average change in particular. It is important now to per year. More complicated trend anal- continue to improve the quality of the ysis methods, such as linear regression results and to maintain full participation or rank correlation techniques, gener- of all counties. ally confirm the findings of the semiquantitative procedure when they are Acknowledgment applied to data sets extended with s u p Before publication, this article was replementary data for up to 10 successive viewed for suitability as an ES&T feature by William E Hunt, Ir., EPA, Research years (9). Triangle Park, N.C. 27711 and John H. All sites with data for five or more Seinfeld, California lnstifute of Technolyears are included in the trend analysis. ogy, Pasadena, Calif. 91125 This includes 63 sites with SOz data and 62 sites with SPM data @th gravimet- Reference (I)UNEPIWHO “Air Quality in Selected Urric and smoke results). ban Areas, 1973-1974,” World Health OrThe predominant trend in the annual ganization Offset Publication 30; Geneva, average data for SOzand SPM is downSwitzerland, 1976. (2) UNEPlWHO “Air Quality in Selected Urward. Downward trends are noted at ban Areas, 1975-1976,” World Health Or54%of the sites for SO2and 43%of the ganization Offset Publication 41; Geneva. sites for particulates. Most of the Switzerland, 1978. changes are in the range of 3-9% per (3) UNEPIWHO “AirQuality in Selected Urban Areas, 1977-1978,” World Health Oryear with fewer ranging from 9% to ganization Offset Publication 57; Geneva, 15% or more per year. Upward trends Switzerland, 1980. occur at 16% of the sites for SO2 and (4) UNEPIWHO “Air Quality in Selected Urban Areas, 1979-1980,” World Health Or10%for particulates. However, at none ganization Offset Publication 75; Geneva, of the sites do SOz and particulate levSwitzerland, 1983. els increase simultaneously. Similar ob- ( 5 ) UNEPIWHO “Selected Methods of Measuring Air Pollutants,” World Health Orgaservations are made with regard to 304 Environ. Sci. Technol.. Vol. 19. No. 4. 1985
nization Offset Publication 24; Geneva, Switzerland, 1976. (6) UNEPIWHO “Air Monitoring Programme Design for Urban and Industrial Areas,” World Health Organization Offset Publication 33; Geneva, Switzerland, 1977. (7) UNEPIWHO “Analysing and Interpreting Air Monitoring Data,” World Health Organization Offset Publication 5 I; Geneva Switzerland, 1980. (8) UNEPlWHO “Estimaing Human E x p e sure to Air Pollutants, World Health Organization Offset Publication 69; Geneva Switzerland. 1982. (9) UNEPlWHO “Urban Air Pollution, 197380”: World Health Oreanization: Geneva. Swiizerland. 1984. (IO) de Koning. H. W.; Kohler, A. Environ. Sci. Techno/. 1978, i Z , 884-89. ( I l l ”Environmental Health Criteria 8: SUI’ phur Oxides and Suspended Particulate Matter”; World Health Organization: Geneva. Switzerland 1979. 112) Journol of ihe Eurooean Communities ’ im, 229.36-48. (13) Fed. Regist. 1911,36. 8186. ~
Burton C. Rennen (I.) !$ o .%eninrp r w grumnie oficrr cfthe Unitrd Nutiom tmtronmrnt Programme and ussoctde dtrrctor o/ the Monrroring und Arcessmrnt Research Centre in London. U K HIS techntral speciality is in pathways analvris and pollutant expo.wre synthesis.
Jan C. kivrnchmar ( K ) IS un enviranmen101 research scientist specializing in air pollution modeling, measurement methods. and data analysts and interpretation. He hac worked in the nuclear and nonnucleur fields at the Nuclear Energ) Research Centre. in Mol. Belgatm. /or the past IO years and is currmtly at Janssen Pharmaceutica. Reerce. Belgium.
G e d G. A W (I.) is dirccror of the Data Management and Analysis Division of EPAs Environmental Monitoring Systems Laboratory. His work involves data mnagement and analysis of air pollution data. He is in charge of operating the data bank for the GEMS air monitoring projecr.
WI de Koning ( E ) is a staffmember of the World Health Organization in Geneva. He joined WHO in 1974 as an air pollutian specialist. His work concerns the development of air pollution prevention and control programs and implementation of the GEMS air monitoring project. Henk
