Vertical profile of peroxyacetyl nitrate (PAN) fromMIPAS-STR measurements over Brazil in February 2005 and its contribution totropical UT NOy partitioning

[摘要] We report on the retrieval of PAN (CH₃C(O)OONO₂) in the uppertropical troposphere from limb measurements by the remote-sensor MIPAS-STR onboard the Russian high altitude research aircraft M55-Geophysica. Themeasurements were performed close to Araçatuba, Brazil, on 17 February2005. The retrieval was made in the spectral range 775–820 cm⁻¹where PAN exhibits its strongest feature but also more than 10 speciesinterfere. Especially trace gases such as CH₃CCl₃, CFC-113, CFC-11,and CFC-22, emitting also in spectrally broad not-resolved branches, make theprocessing of PAN prone to errors. Therefore, the selection of appropriatespectral windows, the separate retrieval of several interfering species andthe careful handling of the water vapour profile are part of the studypresented.

The retrieved profile of PAN has a maximum of about 0.14 ppbv at 10 kmaltitude, slightly larger than the lowest reported values(<0.1 ppbv) and much lower than the highest reported in theliterature (0.65 ppbv). Besides the NO_y constituentsmeasured by MIPAS-STR (HNO₃, ClONO₂, HO₂NO₂, PAN),the in situ instruments aboard the Geophysica provide simultaneousmeasurements of NO, NO₂, and the sum NO_y. Comparingthe sum of in-situ and remotely derivedNO+NO₂+HNO₃+ClONO₂+HO₂NO₂+PAN withtotal NO_y a deficit of 30–40% (0.2–0.3 ppbv) in the troposphereremains unexplained whereas the values fit well in the stratosphere.

[学科分类] 大气科学