Objectives: To carry out a prospective combined quantitative analysis of the associations between all cause mortality and ambient particulate matter and sulphur dioxide.

The APHEA project is supported by the European Union Environment 1991-94 Programme. The project must be placed in the context of recent studies investigating the short term adverse health effects of moderate and relatively low air pollution levels which have consistently indicated the existence of effects at levels below the current national and international air quality guidelines. 1-7 The background and rationale of the study as well as the study areas and air pollution levels have been described in detail elsewhere.8The APHEA project is a multicentre temporal study that uses aggregated data.9 Eleven European groups participate, analysing data from 15 European cities, with a total population over 25 000 000. The objectives of the programme are: * To provide quantitative estimates ofthe short term health effects (using the total and cause specific daily number of deaths and emergency hospital admissions) of air pollution, taking into consideration interactions between different pollutants and between pollutants and other environmental factors. * To further develop and standardise the methodology for the detection of short term health effects in the analysis of epidemiological time series data. * To select and develop a meta-analytic approach for epidemiological time series studies. * To assess the feasibility of creating a European data base of air pollution measurements and of health indicators recorded on a daily basis. This will allow continuous surveillance of short term effects of air pollution in the future.The cities involved in the project are (in alphabetical order): Amsterdam, Athens, Barcelona,

Study objective -To review the issues and methodologies in epidemiologic time series studies of daily counts of mortality and hospital admissions and imustrate some of the methodologies. Design -This is a review paper with an example drawn from hospital admissions of the elderly in Cleveland, Ohio, USA.Main results -The central issue is control for seasonality. Both over and under control are possible, and the use of diagnostics, including plots, is necessary. Weather dependence is probably non-linear, and adequate methods are necessary to adjust for this. In Cleveland, the use of categorical variables for weather and sinusoidal terms for filtering season are illustrated. After control for season, weather, and day of the week effects, hospital admission of persons aged 65 and older in Cleveland for respiratory illness was associated with ozone (RR= 1-09, 95% CI 1-02, 1.16) and particulates (PM,O (RR= 1-12, 95% CI 1-01, 1-24), and marginally associated with sulphur dioxide (SO2) (RR= 1.03, 95% CI=-099, 1-06). All of the relative risks are for a 100 tg/m3 increase in the pollutant. Conclusions -Several adequate methods exist to control for weather and seasonality while examining the associations between air pollution and daily counts of mortality and morbidity. In each case, care and judgement are required.

We investigated the short-term effects of air pollution on hospital admissions for chronic obstructive pulmonary disease (COPD) in Europe.As part of a European project (Air Pollution and Health, a European Approach (APHEA)), we analysed data from the cities of Amsterdam, Barcelona, London, Milan, Paris and Rotterdam, using a standardized approach to data eligibility and statistical analysis. Relative risks for daily COPD admissions were obtained using Poisson regression, controlling for: seasonal and other cycles; influenza epidemics; day of the week; temperature; humidity and autocorrelation. Summary effects for each pollutant were estimated as the mean of each city's regression coefficients weighted by the inverse of the variance, allowing for additional between-cities variance, as necessary.For all ages, the relative risks (95% confidence limits (95% CL)) for a 50 µg·m -3 increase in daily mean level of pollutant (lagged 1-3 days) were (95% CL): sulphur dioxide 1.02 (0.98, 1.06); black smoke 1.04 (1.01, 1.06); total suspended particulates 1.02 (1.00, 1.05), nitrogen dioxide 1.02 (1.00, 1.05) and ozone (8 h) 1.04 (1.02, 1.07).The results confirm that air pollution is associated with daily admissions for chronic obstructive pulmonary disease in European cities with widely varying climates. The results for particles and ozone are broadly consistent with those from North America, though the coefficients for particles are substantially smaller. Overall, the evidence points to a causal relationship but the mechanisms of action, exposure response relationships and pollutant interactions remain unclear.

Asthma morbidity has been increasing for Background -A study was undertaken to reasons not yet well understood.1 Although assess the combined association between evidence for an increasing incidence of asthma urban air pollution and emergency ad-due to air pollution has not been provided, air missions for asthma during the years pollution could exacerbate existing asthma. to sulphur dioxide (SO 2 ), ozone (O 3 ), and Methods -Daily counts were made of nitrogen dioxide (NO 2 ) at levels compatible asthma admissions and visits to the emer-with urban life produced bronchial hypergency room in adults (age range 15-64 responsiveness and inflammation and reduced years) and children (<15 years). Covari-the dose of aeroallergen needed to produce ates were short term fluctuations in tem-a given bronchial response.3-9 Studies on air perature and humidity, viral epidemics, pollution in laboratory face two main limday of the week effects, and seasonal and itations: the non-representative selection of secular trends. Estimates from all the cities subjects and the simplification of human exwere obtained for the entire period and posures. separately by warm or cold seasons using Some recent population studies have related Poisson time-series regression models. daily levels of particles and ozone to the increase Combined associations were estimated of emergency room admissions for asthma, using meta-analysis techniques.though these findings do not extend to all Results -Daily admissions for asthma in the studies.2 10 Epidemiological studies on daily adults increased significantly with in-variations in asthma admissions and air polcreasing ambient levels of nitrogen dioxide lution levels assess the general population at (NO 2 ) (relative risk (RR) per 50 g/m 3 in-real world exposures with adequate internal crease 1.029, 95% CI 1.003 to 1.055) and validity.11 12 The APHEA Project 13 is an internon-significantly with particles measured national European prospective standardised as black smoke (RR 1.021, 95% CI 0.985 to study on the short term health effects of air 1.059). The association between asthma pollution in the general population. This paper admissions and ozone (O 3 ) was hetero-combines the individual city associations of air geneous among cities. In children, daily pollution with asthma admissions in Barcelona, admissions increased significantly with Helsinki, London and Paris, the four European sulphur dioxide (SO 2 ) (RR 1.075, 95% CI cities in APHEA that collected data on asthma. 1.026 to 1.126) and non-significantly with This multi-city study allows an evaluation of a black smoke (RR 1.030, 95% CI 0.979 to wide variability in environmental exposures and 1.084) and NO 2 , though the latter only in enhances the external validity of findings. cold seasons (RR 1.080, 95% CI 1.025 to Individual results have been reported for 1.140). No association was observed for O 3 . Helsinki 14 and Barcelona.