CLIMATOLOGICAL ASPECTS OF THE DAYTIME MIXING HEIGHT IN BUENOS-AIRES CITY, ARGENTINA

An analysis of the climatic behavior of different parameters related t o air quality in Buenos Aires city is presented. The principal statist ical characteristics of hourly daytime mixing height distributions are studied. The cumulative frequencies of hourly daytime mixing height r anges are calculated. The frequencies of occurrence of daytime atmosph eric stability conditions are obtained. An analysis of mixing heights and related atmospheric stability conditions is presented. The obtaine d mean mixing heights and standard deviations are smaller in winter an d higher in summer. The lowest mixing heights occur in the morning wit h an increasing trend until the maximum at 14-15 LT and a slower decre asing rate toward sunset. The highest hourly daytime mean values deriv ed for summer and winter, respectively, are 1170 and 592 m. The lowest are 547 and 261 m. The obtained standard deviations range from 289 to 638 m in summer and from 144 to 382 m in winter. The most commonly oc curring mixing heights for a given time of the day are lower than the corresponding mean mixing heights and occur in the range 333-833 m in summer and 205-349 m in winter. There is an elevated frequency of occu rrence of daytime mixing heights below 1500 m (99% in winter and 85% i n summer). The more frequent daytime stability conditions are the near neutral, slightly unstable and unstable (96% in winter and 94% in sum mer). These stability conditions are associated with mixing heights be low 1500 m. The smallest mean daytime mixing heights by stability cate gory occur during winter, while the largest are obtained in summer, ra nging, respectively, between 330 and 486 m and 716 and 1037 m. (C) 199 8 Elsevier Science Ltd. All rights reserved.