On the use of data from commercial NOx analyzers for air pollution studies
2019
Dickerson, Russell R. | Anderson, Daniel C. | Ren, Xinrong
Reactive oxidized nitrogen species play a central role in environmental pollution, and long term monitoring is common, but commercial NOx analyzers employing heated converters respond to many species in addition to the compounds NO and NO2, taken together and defined as NOx. The response of these instruments to other gases including nitric acid, peroxyacetyl nitrate, and alkyl nitrates (the sum of these plus NOx is defined as NOy) is well established, but the ratio of NOx to NOy varies in time and space making the accuracy of commercial NOx monitors uncertain. Care must be taken when comparing spectroscopic measurements of NO2 or numerical models to output from conventional NOx monitors. Correction factors can be developed for specific conditions, and long term trends can be meaningful. Recent studies comparing modeled NOx to measurements with large interferences (more nearly NOy) can involve errors of a factor of two or more, adding urgency to the deployment of “true NOx” monitors.
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