With the start of the 21th century, the focus of atmospheric satellite missions has shifted gradually from the stratosphere (ozone chemistry) to the troposphere (air quality, aerosols, clouds, greenhouse gases). With this new situation NASA and ESA have identified a number of gaps in the satellite validation infrastructure for reactive trace gases such as nitrogen dioxide, ozone, sulfur dioxide, formaldehyde, etc. Studies have shown that due to the intrinsic difference in the field of view between satellite and ground data, large statistics (long time series at many locations) are needed in order to perform meaningful validation activities. This is especially true for (spatially and temporally) highly variable species such as nitrogen dioxide. Therefore it was concluded that a large-scale global monitoring network of (quasi-)autonomous stations is needed. Such a network did not exist for those species, with the exception of the Dobson/Brewer network for total ozone column measurements.
In 2005 NASA initiated an effort at Goddard Space Flight Center (GFSC) to address this issue by starting to develop a cost-effective, compact, easy to deploy, ground-based, passive remote sensing spectrometer system capable of performing sun, moon and sky observations called “Pandora”. Pandora has continuously evolved since then with support from NASA and ESA and has been manufactured by SciGlob LLC, Elkridge, MD, USA since 2010. Soon Pandoras were distributed around the globe to form a validation network. In 2013 ESA joined NASA in funding this development through prime contractor LuftBlick OG, Innsbruck, Austria. Since 2018, this network is called “Pandonia Global Network” (PGN) and endeavors to ensure systematic processing and dissemination of the data to the greater global community in support of air quality monitoring and satellite validation. The PGN is carried out jointly by NASA and ESA as part of their “Joint Program Planning Group Subgroup” on calibration and validation and field activities, with additional collaboration from other institutions, most notably via the US Environmental Protection Agency (EPA) integration of instruments at long-term air quality monitoring stations.
The PGN provides real-time, standardized, calibrated and verified air quality data and associated uncertainty values. In the context of satellite validation PGN data sets are representing Fiducial Reference Measurements. PGN also seeks to coordinate and implement network standards regarding common algorithms and data processing, instrument operating routines, quality control, real-time data processing and data archiving. The instruments of the PGN are owned and operated by a large number of individual participating institutions (see the PGN distribution map). Participation in the PGN, which is open to anybody, entitles the instrument owner to receive support in instrument installation, operation, and maintenance by the PGN team and ensures that data produced by that instrument will be calibrated, processed, visualized, and distributed on the PGN central server. If you are interested in joining the PGN, contact any person listed in the “Contacts” section or simply write to operation[at]pandonia-global-network.org!