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A novel, multistage, dielectric, packed-bed, plasma reactor has been developed and is used to efficiently destroy environmental pollutants, such as volatile organic compounds (VOCs). A three cell plasma reactor, operated at ambient pressure and low temperatures, is found to be an effective technology for complete VOC remediation in air. The combination of plasma cells in series can significantly improve the efficiency of VOC decomposition, but the combined destruction rate is not simply an additive effect, there is a synergistic enhancement related to the effect on the plasma chemistry of sequential processing in the three cells. At the same time, the formation of byproduct such as NOx is strongly suppressed, and it is possible to remediate toluene and ethylene in air, with no detectable formation of NOx or nitric acid.

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A nonthermal, atmospheric pressure, packed-bed plasma reactor has been used to study the effect of temperature on the plasma−catalytic destruction of toluene and benzene in air. The plasma reactor was packed with BaTiO3 beads to which TiO2, γ-Al2O3, and Ag, Pt, or Pd impregnated catalysts were added. The reactor can be heated up to ∼500 °C, and the destruction efficiencies for toluene and benzene were determined for plasma alone, catalyst alone, and the combined plasma−catalyst configuration. Comparisons have been made to determine the relative contributions of the catalyst and plasma and to discover any synergistic effects. Plasma−catalysis shows greater destruction than catalysis alone with increasing temperature for both benzene and toluene. Catalysis alone has a threshold temperature of ∼300 °C for the destruction of toluene and benzene, but plasma−catalysis with Pd- and Pt-impregnated alumina achieves >95% destruction at this temperature and has a threshold of ∼100 °C. Toluene is more easily destroyed than benzene at all temperatures, by all catalysts.

There is a high international priority attached to activities which reduce NOx in the atmosphere. The current level of permitted emissions is typically between 50 µmol/mol and 100 µmol/mol, but lower values are expected in the future. Currently, ambient air quality monitoring regulations also require the measurement of NOx mole fractions as low as 0.2 µmol/mol. The production of accurate standards at these levels of mole fractions requires either dilution of a stable higher concentration gas standard or production by a dynamic technique, for example one based on permeation tubes.The CCQM-K74 key comparison was designed to evaluate the level of comparability of National Metrology Institutes' measurement capabilities and standards for nitrogen dioxide (NO2) at a nominal mole fraction of 10 µmol/mol.The measurements of this key comparison took place from June 2009 to May 2010.Seventeen laboratories took part in this comparison coordinated by the BIPM and VSL. The key comparison reference value was based on BIPM measurement results, and the standard measurement uncertainty of the reference value was 0.042 µmol/mol.This key comparison demonstrated that the results of the majority of the participants agreed within limits of ±3% relative to the reference value. The results of only one laboratory lay significantly outside these limits. Likewise this comparison made clear that a full interpretation of the results of the comparison needed to take into account the presence of nitric acid (in the range 100 nmol/mol to 350 nmol/mol) in the cylinders circulated as part of the comparison, as well as the possible presence of nitric acid in the primary standards used by participating laboratories.Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCQM, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

A nonthermal, atmospheric pressure plasma, made-up of a BaTiO3 packed-bed reactor, has been used to study the formation of NOx and N2O during the plasma destruction of a range of volatile organic compounds (VOCs) and hazardous air pollutants, including chlorinated, brominated, fluorinated, and iodinated methane species, in a carrier gas of air. Using the plasma destruction of pure air as a baseline, it is found that the amount of NOx formed is unaffected by the addition of a few hundred parts per million of a simple hydrocarbon (e.g. methane). In the case of the fluorinated, chlorinated, and brominated methanes, we find enhanced production of NOx and a marked increase in the ratio of NO2 to NO formed, from approximately 1.1 in air and methane to approximately 2.3 in halogenated species. However, iodinated additives (specifically methyl iodide and diiodomethane) have remarkably different results compared to the other halogenated additives; they show enhanced increases in the NO2 to NO ratio ( approximately 6-13) and reduced NOx production. The enhanced conversion of NO to NO2 is attributed to reactions involving halogen oxides, e.g. ClO and IO.

A non‐thermal, atmospheric‐pressure plasma has been used to study the effect of temperature on the plasma destruction of DCM in an air stream using a BaTiO3 packed‐bed reactor, co‐filled with TiO2 and γ‐Al2O3 catalysts. Comparisons have been made with plasma alone, catalysis alone and combined plasma/catalysis to determine any synergistic effects of combining plasma and catalysis. Plasma/catalysis is the most successful method for destroying DCM over 125–400 °C. TiO2 was more effective than γ‐Al2O3 for plasma/catalysis. The energy efficiency of plasma/catalysis processing compared to catalysis alone is considered by examining the input power required to achieve equivalent destructions, finding that an energy reduction of ≈30% can be achieved by plasma activation of the catalyst.magnified image