The yields of alkyl nitrates formed in the NOx-air photooxidations of the homologous series of n-alkanes from ethane through n-octane have been determined at 299 ± 2 K and 735 torr total pressure for two different chemical systems. Alkyl peroxy radicals were generated by reaction of the n-alkanes with OH radicals (generated from the photolysis of methyl nitrite in air) or Cl atoms (from photolysis of Cl2 in air). The alkyl nitrate yields obtained from the two systems, corrected for secondary reactions, were in agreement within the experimental errors and increased monotonically with the carbon number of the n-alkane, from <1% for ethane to ~33% for n-octane, with the yields apparently approaching a limit of ~35% for large n-alkanes. The relative yields of the various secondary alkyl nitrate isomers in the n-pentane through n-octane systems were in good agreement with those expected from OH radical or Cl atom reaction with the corresponding secondary C-H bonds. However, the relative yields of the primary alkyl nitrates in the propane and butane systems were a factor of ~2 lower than expected. The data are consistent with the alkyl nitrates being formed almost entirely from the reaction of peroxy radicals with NO, and the ratios of the corrected alkyl nitrate yields thus reflect the fraction of R02 radicals which react with NO to form alkyl nitrates. These nitrate yields from the reaction of R02 radicals with NO are important inputs into chemical computer models of the atmospheric NO*-air photooxidations of the large n-alkanes.

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Biofiltration is a relatively recent air pollution control (APC) technology in which off-gases containing biodegradable volatile organic compounds (VOC) or inorganic air toxics are vented through a biologically active material. This technology has been successfully applied in Germany and The Netherlands in many full-scale applications to control odors, VOC and air toxic emissions from a wide range of industrial and public sector sources. Control efficiencies of more than 90 percent have been achieved for many common air pollutants. Due to lower operating costs, biofiltration can provide significant economic advantages over other APC technologies if applied to off-gases that contain readily biodegradable pollutants in low concentrations. Environmental benefits include low energy requirements and the avoidance of cross media transfer of pollutants. This paper reviews the history and current status of biofiltration, outlines its underlying scientific and engineering principles, and discusses the applicability of biofilters for a wide range of specific emission sources.

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