ENVIRONMENTAL POLLUTION Environmental Pollution 101 (1998) 183-191 A synoptic climatological approach to forecast concentrations of sulfur dioxide and nitrogen oxides in Hong Kong Kin-Che Lam *, Shouquan Cheng zyxwvutsrqponmlkjihgfedcbaZYXWVU Department of Geography, The Chinese University of Hong Kong, Shatin, New Territories, Hong Kong, China Received 4 December 1997; accepted 13 April 1998 Abstract The objective of this study is to develop an automated synoptic climatological procedure to forecast high air pollution con- centrations in the most polluted synoptic categories. The procedure is able to identify air masses historically associated with high air pollution concentrations. The arrival of air mass can be predicted 24 or 48 h in advance with the use of the weather forecast data. The development and statistical basis of the procedure are discussed, and an analysis of the procedure’s ability to forecast weather conditions associated with high air pollution concentrations is presented. In addition, the dataset of 24 weather variables from 1993 to 1995 is used to validate the procedure. The procedure predicts that 70.3 and 83.3% of total high and severe SO2 concentration days fall into the identified most polluted categories, and the corresponding figures for NO, are 47.8 and 73.7%. The agreement between observed and predicted values is generally good. The prediction models can explain about 58 and 45% of total variance for NO, and SO1with RMSEs of 42.5 and 16.5 bgrnp3, respectively. They are smaller than 1 SD of the observations. 0 1998 Elsevier Science Ltd. All rights reserved. Keywords: Climatic indices; Discriminant function analysis; Principal component analysis; Clustering procedure; Air masses; Air pollution prediction 1. Introduction The synoptic climatological classification approach has become a popular tool in the evaluation of the impact of climate on air pollution concentrations because it can categorize a complex set of meteor- ological variables as a coherent index (Kalkstein, 1979; Perry, 1983; Yarnal, 1993). A synoptic categorization accentuates homogeneity in weather type or air mass and facilitates analyses of climatic impact on a wide variety of environmental problems, such as air quality (Kalkstein and Corrigan, 1986; Kalkstein et al., 1990a; Powley, 1991; Cheng et al., 1992; Eder et al., 1993, 1994; Cheng and Lam, 1997), climate change (Kalkstein et al., 1990b; Cheng and Kalkstein, 1993), and human health (Kalkstein, 1991a; Cheng, 1991; Kalkstein et al., 1994; Nichols et al., 1995). In a recent investigation (Cheng and Lam, 1997) using principal component analysis (PCA) and a clus- tering procedure, we classified the climatic data of Hong Kong based on 24 weather variables from 1983 to 1992 * Corresponding author. Tel.: (852) 26094458; fax: (852) 2603- 5006; e-mail: kinchelam@cuhk.edu.hk 0269-7491/98/S19.00 0 1998 Elsevier Science Ltd. All rights reserved. PII: SO269-7491(98)00087-6 into 15 distinctive major synoptic categories. This pro- cedure was able to identify the synoptic categories associated with particularly high air pollution con- centrations. The stepwise regression analysis within the most polluted categories has shown a strong synoptic category relationship with air pollution concentrations, which indicates that the regression models can be used to predict air pollution concentrations. Many previous studies have used qualitative and semiquantitative methods to evaluate the meteor- ological conditions associated with high pollution con- centrations from a synoptic perspective (Sanchez et al., 1990; Pissimanis et al., 1991; Kallos et al., 1993). Another well-established approach attempts to deter- mine a relationship between air pollution concentra- tions and various meteorological parameters to predict the concentrations (Aron and Aron, 1978; Aron, 1984; Robeson and Steyn, 1990; Comrie, 1994; Ziomas et al., 1995). Some of these models are purely empirical and do not attempt to explain the mechanisms involved (Zio- mas et al., 1995). The use of individual weather vari- ables poses a different dilemma, because air pollutants are known to respond to the entire suite of meteor- ological elements which comprise an air mass, rather