Ozone (O3) is a secondary gaseous pollutant in the urban environment, and its variation correlates well with nitrogen oxides (NOx = NO + NO2). Continuous monitoring has been done in the Campo Grande city urban area, using ozone 49C and NO-NO2-NOx 42CTL gas analyzers. The results show that the maximum concentrations of O3 and oxidant (Ox = O3 + NO2) in Campo Grande often appear in the early afternoon around 15:00 hours. The daily variation of NO concentrations shows a very clear cycle with two peaks, one appearing around 07:00 a.m. and the other at 11:00 p.m. At the lowest level, NO2 is the main component of NOx, while NO dominates the higher mixing ratio. It is also shown that the level of Ox is composed of two factors: the regional and the local contributions. The former is affected by the regional O3 level, while the latter is effectively correlated with the primary pollution level. The daily variation also appears in the concentrations of oxidant components.

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We report the observation of magnetophonon resonances on the background of the longitudinal magnetoconductance in short-period GaAs/AlAs semiconductor superlattices. Both the GaAs and the AlAs longitudinal optical phonons are observed. We show how the enhancement of the magnetophonon effect with electric field is connected to the shift of the electron distribution towards the high-velocity and low-density-of-states region at the midpoint of the reduced Brillouin zone. The observed temperature dependence can be explained by considering the competition between the phonon population and the electron lifetime. The two superposed series of the GaAs and the AlAs optical phonons are shifted when hydrostatic pressure is applied and the relative strength of each series changes as the ⌫ miniband comes closer to the X states.