Validation of NO2 vertical profiles from PGN and MAX-DOAS using tethered-balloon measurements in Bangkok during the GEMS-AQ campaign

In February 2026, a field campaign called the Geostationary Environment Monitoring Spectrometer - Air Quality (GEMS-AQ) was conducted in Bangkok, Thailand, to investigate the causes of worsening air quality in Southeast Asia. This campaign was part of a broader effort to combine satellite, aerial, and ground-based observations to better understand air pollution dynamics in the Bangkok megacity. One of our research objectives was to validate the diurnal variations of NO2 vertical profiles retrieved from ground-based multi-axis differential optical absorption spectroscopy (MAX-DOAS) using the JAMSTEC MAX-DOAS network algorithm (JMNet1) and Pandora official products by comparing them with in-situ measurements. To achieve this, we deployed a tethered balloon equipped with a Portable cavity-enhanced Absorption of Nitrogen Dioxide Analyzer (PANDA) based on incoherent broadband cavity-enhanced absorption spectroscopy (IBBCEAS), which is lightweight and suitable for vertical profiling measurements. One of the advantages of the tethered balloon system is its ability to capture the temporal evolution of the NO2 layer during daytime up to approximately 1.3 km, close to the planetary boundary layer (PBL) height. These results will help improve the accuracy of NO2 tropospheric vertical column density estimates from GEMS by updating a priori NO2 vertical profiles to better reflect real-world conditions.