The diurnal variation of the structure of pollutant transport and diffusion in the Ohio River Valley is examined by combining meteorological cross sections with vertical profiles of several air pollutants. An increased frequency of rawinsonde releases from NWS stations at Salem, Dayton and Pittsburgh during the period 1–10 August was supplemented on 5 and 6 August by vertical profiles taken along the cross-section line by an aircraft. The data on 5 August, a day without convective activity to complicate analyses, merit special study. Analyses of the bscat structure superimposed on the meteorological cross sections lend support to the theory of horizontal transport of polluted layers above the nocturnal inversion or developing mixed layer without significant dilution. The effect of the daily breathing of the planetary boundary layer on the vertical structure of pollutants can be seen in the sequence of cross sections.