Technical note: Evaluation of standard ultraviolet absorption ozone monitors in a polluted urban environment

[摘要] The performance of the EPA Federal Equivalent Method (FEM) technique formonitoring ambient concentrations of O₃ via ultraviolet absorption (UV)has been evaluated using data from the Mexico City Metropolitan Area field campaign (MCMA-2003). Comparisons of UV O₃ monitors with openpath Differential Optical Absorption Spectroscopy (DOAS) and open pathFourier Transform Infrared (FTIR) spectroscopy instruments in two locationsrevealed average discrepancies in the measured concentrations between +13% to−18%. Good agreement of two separate open path DOAS measurements at onelocation indicated that spatial and temporal inhomogeneities were notsubstantially influencing comparisons of the point sampling and open pathinstruments. The poor agreement between the UV O₃ monitors and the openpath instruments was attributed to incorrect calibration factors for the UVmonitors, although interferences could not be completely ruled out. Applyinga linear correction to these calibration factors results in excellentagreement of the UV O₃ monitors with the co-located open pathmeasurements; regression slopes of 0.94 to 1.04 and associated R²values of >0.89. A third UV O₃ monitor suffered from large spuriousinterferences, which were attributed to extinction of UV radiation withinthe monitor by fine particles (<0.2 µm). The overall performance ofthis particular monitor was poor owing to a combination of interferencesfrom a contaminated particle filter and/or ozone scrubber. Suggestions forimproved operation practices of these UV O₃ monitors andrecommendations for future testing are made.

[学科分类] 大气科学