NOx, NO and NO2 concentrations, and meteorological parameters, temperature, wind speed, relative humidity and pressure were measured simultaneously and continuously in Dhahran (Saudi Arabia) during three months in summertime. The hourly and daily NOx, NO and NO2 average concentrations were investigated as a function of the meteorological parameters. NOx, NO, and NO2 were found to have a common source and to be highly influenced by traffic emission and meteorological conditions, and the trend of NO showed a higher concentration during weekdays than weekends. NOx has significant positive correlation coefficients with NO and NO2, respectively. Similarly, NO2 also has a positive correlation coefficient with NO. The temperature and wind speed showed negative correlation coefficients while relative humidity showed positive correlation coefficient with NOx, NO and NO2. On the other hand, NO2 was found to exceed international air quality standards, which indicates the existence of a possible NO2 air pollution problem in Dhahran.
Many-fold enhancements in the population densities of O atoms in low-pressure glow discharges in Ar–O2 and He–O2 compared with the discharge in pure O2 have been reported in recent years. In some reports, the 3sS3,5–3pP3,5 transitions of O atoms around 844.6 or 777.2nm are considered in estimating the density of atomic oxygen. The authors’ results demonstrate that the contributions of other possible transitions such as 3sS3,5–npP3,5 (n>3) directly feeding the lower 3sS3,5 levels are also significant and should be included for a better estimate of O atom densities.
Sound resonance in pipes is investigated using a readily available setup consisting of a pipe, loudspeaker, microphone, and laptop. Discrete Fourier transform is used to extract the amplitude and phase spectra from the recorded sound enabling determination of locations and shapes of resonance peaks accurately. Either white noise signal or sharp pulse signal is used as an excited input sound signal. Both have broad frequency spectra and the difference between them is explored. The shapes of the amplitude and phase spectra are found to be well fitted to the predicted shapes. The pipe is either closed at both ends, closed at only one end, or open at both ends. The speed of sound and the effective location of reflection at the open end are in excellent agreement with theory.
Low-pressure glow discharges in He, Ne, or Ar gases containing small amounts of O2 can produce considerable dissociation of O2 molecules. High-lying metastable states in these noble gases play a predominant role in this process. Due to the difference in energies of metastable states of the noble gas atoms, there is a significant variation in the product states of O atoms created as a result of dissociation. Apparently, for He and Ne, superexcited O2 molecules are formed through collisions with high-lying metastable states of the noble gases. The superexcited O2 molecule could either autoionize to form an O2+ ion that subsequently captures an electron and dissociates or it could directly dissociate through some curve-crossing interactions yielding at least one atom in highly excited state. However, in the case of Ar, the formation of superexcited O2 may be possible through a prior creation of Ar2+ ion. We report some interesting observations on spectral emissions from O atoms in the three gas mixtures covering transition from 5d, 4d D3,5, and 5s S3,5, to 3p 3,5P levels and 4p and 3p P3,5 to 3s S3,5 levels. The emission from the b Σ4g−−a Π4u system of O2+ ions is also reported. In general, populations of the above-stated O and O2+ levels are highest in the case of He–O2 mixture and lowest for the Ar–O2 mixture. However, the Ne–O2 mixture appears to strongly populate the 4p P5 levels, while the Ar–O2 mixture strongly populates the 3p P3 levels. The He–O2 mixture appears to be more efficient among the three gas mixtures considered in dissociating the O2 molecules.
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