Ozone aircraft sampling

For any event to be accurately recorded, it must persist for the pulse time of the instrument. This time is equal either to the rise time or to the time to 100% response, depending on the design of the instrument. For accurate data from aircraft sampling plumes, for example, it is necessary to obtain rise times of a few seconds or less. This is a very fast response for an analyzer and has only recently become possible for ozone measurements. 

All alkanes measured below canopy. b Above canopy as determined by aircraft sampling. c On days when ozone levels were near background values. d On days when ozone levels exceeded background values. In ppbv of carbon. 

The Montreal Protocol of July 1987 resulted in an international treaty in which the industrialized nations agreed to halt the production of most ozone-destroying chlorofluorocarbons by the year 2000. This deadline was hastily changed to 1996, in February 1992, after a U.S. National Aeronautics and Space Administration (NASA) satellite and high-altitude sampling aircraft found levels of chlorine monoxide over North America that were 5i % greater than that measured over Antarctica. 

Most of the atmospheric oxidant and ozone data—as well as the experimentally determined exposure data for v tation, animals, and humans—have been obtained with analyzers that sample and record the ambient concentrations almost continuously during the period of observation. The response times are usually acceptable for fixed-station monitoring, because data describing hourly averages are sufficient. Faster responses are needed, however, for studying chemical reaction rates, retention on inhalation, sampling while in motion (as from aircraft), and expediting calibrations. The response times required are therefore a function of the resolution needed. 

This is carried out by operating a chemiluminescent NOj analyzer (cf. NO, analysis) at a NO excess condition. As the reaction of ozone with NO is faster and gives more intense CL than that with ethene, this method is preferred for some purposes in which a fast response is required (i.e., aircraft flux measurements). However, this CL method is subject to interference from water vapor and may contaminate the environment with NO. The ozone-NO reaction is also known as a gas-phase titration reaction, in which sample gas is mixed with a low-concentration standard NO gas and the NO2 formed in quantities equivalent to ozone is determined by an appropriate method. While CL reactions of ozone with other alkenes, alkyl sulfides, phosphine, arsine, and stibine... 

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