10.2190/2RF8-9XJK-6W6V-MXYF 2RF89XJK6W6VMXYF 3 An Investigation of Changes in Air Particulate Concentrations in Chicago 269 290 20020509 20020509 20020509 20020509 2RF89XJK6W6VMXYF.pdf http://baywood.metapress.com/link.asp?target=contribution&id=2RF89XJK6W6VMXYF 3 Ivan I. Saavedra-Cuadra A. Ramachandra Rao School of Civil Engineering, Purdue University Changes in monthly averages of total suspended participates in Chicago are analyzed to investigate the effect of a law forbidding the use of high sulphur coal, which came into effect in January 1970. A seasonal integrated autoregressive-moving average time series model is fitted to the data collected prior to 1970 and forecasts made from this model are compared with the data observed after the ban was in effect. A portmanteau test based on one-month ahead forecast errors indicates the decrease in particulate concentrations caused by the law banning the use of high sulphur coal to be statistically significant. Weight functions which represent the effects of changes in parameters of the model and changes in the series due to different factors modeled by a series of indicator variables are computed next. These weight functions are used to analyze the one-step ahead forecast error variance in order to evaluate the magnitude of changes in the long-term trend and seasonality of the particulate data. The results indicate a gradual decrease in the particulate emissions due to high sulphur coal burning that approaches steady-state after an approximate lag of five years. W. D. O'Neill, Time Series Modeling of Chicago Particulates, <i>Journal of the Environmental Engineering Division, ASCE, 105</i>:EE5, pp. 885-866, 1979. A. R. Rao and G. Padmanabhan, Intervention Analysis of Total Suspended Particulate Data from Chicago, <i>Atmospheric Environment, 17</i>:3, pp. 563-572, 1983. G. C. Tiao, G. E. P. Box, and W. J. Hamming, Analysis of Los Angeles Photochemical Smog Data: A Statistical Overview, <i>Journal of the Air Pollution Control Association, 25</i>, pp. 260-268, 1975. G. E. P. Box and G. M. Jenkins, <i>Time Series Analysis, Forecasting, and Control</i>, Holden-Day, San Francisco, California, 1975. G. E. P. Box and G. C. Tiao, Comparison of Forecast and Actuality, <i>Applied Statistics, 25</i>:3, pp. 195-200, 1976. R. Roy and J. Pellerin, Long Term Air Quality Trends and Intervention Analysis, <i>Atmospheric Environment, 16</i>:1, pp. 161-169, 1982.