CHEMICAL AMPLIFIERS FOR DETECTION OF PEROXY-RADICALS IN THE ATMOSPHERE

The chemistry of atmospheric odd-hydrogen radicals (HO, HO2, RO, and RO2) has been the focus of much attention in recent years due to their pivotal role in tropospheric air pollution. A chemical amplification system that uses a chain reaction initiated by the reaction of HO2 with NO to form NO2 and HO radicals has been shown to have potential as a monitor for peroxy radicals in the troposphere. The HO radicals produced react with a chain-carrying agent to re-form peroxy radicals and thus restart the chain. Previous work in this field has used CO as the chain carrier and demonstrated the potential of this approach in the atmosphere. Presented here are the results of a modeling study on a series of alternative chain-carrying agents: ethene, propene, ethanol, and dimethyl ether. The final NO2 concentration was determined for each of the chain carriers over the range of HO2 concentrations of atmospheric interest [(1-50) X 10(7) molecule cm-3]. The chain lengths predicted were higher than those obtained for CO, typically by a factor of 2.5. In addition, the sensitivity of the chain length to the initial concentrations of the organic chain carrier and NO was predicted to be small. Interferences from atmospheric pollutants were also assessed.