OZONE LEVELS IN CHONGQING - A POTENTIAL THREAT TO CROP PLANTS COMMONLY GROWN IN THE REGION

Chongqing, a city with a population of > 2.5 million, constitutes the biggest industrial and commercial centre in southwest China. Recent in dustrialization has led to an increasing air pollutant problem which i s exacerbated by the topography and prevailing climate of the region. To date, interest has remained firmly focused on the levels of traditi onal air pollutants (sulphur dioxide [SO2], oxides of nitrogen [NOx], smoke and suspended particulate matter [SPM]), with little attention p aid to photochemical oxidants such as ozone (O-3) This paper reports t he first assessment of ambient O-3 levels in southwest China. Measurem ents were made in and around Chongqing using a combination of UV-absor ption (at a site located in the northern sector of the city) and passi ve samplers (at 20 sites located in and around the city) between 1993 and 1996. The 7-h daily mean O-3 concentrations ranged between 2 and 1 6 ppb (x10(9)) during the winter months, increasing to 18-41 ppb durin g the summer (June-August), when peak hourly mean O-3 concentrations o f 93 ppb were attained. Ozone exposures across the region commonly app roached (or exceeded) UN-ECE and WHO short-term guidelines for the pro tection of crops. In addition, controlled chamber studies, in which 11 cultivars of Chinese crops commonly grown in the Chongqing region wer e screened for relative O-3 sensitivity, indicated the potential for s ubtle effects on the growth of a number of crop plants, if ambient O-3 levels continue to rise in the region. Employing ozone exposures some what higher than those experienced in the held, several cultivars of c ommonly grown Chinese cereal, vegetable and salad crops were found to be sensitive to O-3 in terms of growth, but this was not always associ ated with the appearance of visible symptoms of injury and, in contras t to what was generally expected, only three species showed significan t O-3-induced reductions in root:shoot partitioning. There is a clear and urgent need for a comprehensive study of ambient air quality and i ts impact on crops and natural vegetation in this, as in other, rapidl y developing regions of China. (C) 1998 Elsevier Science Ltd. All righ ts reserved.