Methods for the monitoring of peroxy radicals and measurement of NO�2 photolysis in the atmosphere.

Chemical amplification, which has been investigated as a method for detecting atmospheric peroxy radicals is based on the following chain reaction, where RH is an organic species: Previous work has used carbon monoxide (CO) as a chain carrier, although larger chain lengths, and thus greater sensitivity, can be a expected for certain organic species. This is predicted by faster rates for reaction (3) that would reduce the influence of chain termination reactions, and more complex secondary chemistry, that could yield more than one peroxy radical for each cycle of the chain. The experimental work used dimethyl ether (DME) as the chain carrier, as well as CO for comparison, while radicals were generated by the photolysis of ethanal in the presence of oxygen. Under identical conditions DME gave a chain length (1400) almost three times that of CO (475). The responses of the system to the initial concentration of NO (0.6-10pmm), and to the duration of the photolysis (l-25ms) were also investigated. It was found that, over the range of concentrations investigated, greater concentrations of NO gave longer chain lengths although longer photolysis periods produced shorter chain lengths. Computer models used to simulate the chemistry were found to closely reproduce the experimental data. In addition, models were constructed for several other organic species; ethene, propene, ethanol and ethyne. Using these models, all six compounds were examined for their responses to reactor conditions and interference from pollutants, such as ozone, peroxyacetyl nitrate (PAN) and peroxynitric acid (PNA). While the alkenes gave consistently higher chain lengths under pollutant-free conditions, they were also the most susceptible to interferences. The best combination of high chain length, and low interference was shown by DME. In addition, the photolysis of N 02 in the presence of 2-butyne (CH3OhCH3) was investigated, as a means of simplifying the measurement of the ambient N 02 photolysis rate. If the concentration of 2-butyne is chosen correctly, all the 0 (3P) produced by the photolysis reacts with it, rather than with more N 02