## 1 Introduction
the orbits from PPP-B2b were approximately 6 cm and 21 cm in the radial and cross-track directions, respectively, for both GPS and BDS-3. In the along-track direction, the RMSEs were approximately 24 cm and 34 cm for BDS-3 and GPS, respectively. In terms of the clock products, the standard deviations (STDs) of the PPP-B2b clocks were 0.11 ns and 0.13 ns for BDS-3 and GPS, respectively. Recent studies [36; 37] also indicate that the average positioning accuracy of static PPP with PPP-B2b corrections is better than 3 cm in the north, east, and upwards directions. This good positioning performance means that tropospheric information could be accurately estimated in real time using the PPP-B2b service, a feature that would be useful in areas without reliable internet connections for weather forecasting and atmospheric studies. The retrieval performance of ZTD in China has been subject to analysis in several studies. [PERSON] et al. [39] reported a RMS difference of 17.4 mm between ZTD values derived using the PPP-B2b service and those estimated by IGS across nine stations from DOY 195 to DOY 200. [PERSON] et al. [40] conducted an analysis of ZTD values derived from PPP-B2b against those provided by the Wuhan University (WHU) analysis centre at eight stations from DOY 187 to DOY 191 in 2021, finding an RMS within 20 mm for stations located in China. However, these investigations are predominantly constrained by their short temporal scope (e.g., one week) and regional focus on China. Given that the effective coverage area of PPP-B2b is not clearly delineated and considering the crucial importance of its temporal stability for operational applications, a more comprehensive study encompassing a broader spatial distribution and extended temporal duration is warranted. This study conducted a comprehensive investigation into the performance of PPP-B2b corrections, focusing on their application in ZTD/PWV estimation across 32 widely distributed stations over approximately one year. The accuracy of BDS-3, GPS orbit, and clock correction from PPP-B2b was assessed using geodetic benchmark (GBM) products from Deutsches Geo-ForschungsZentrum (GFZ) as a reference. Previous studies have demonstrated centimetre-level agreement between orbit/clock products from different analysis centres, with static positioning results showing only centimetre-level differences between products from the Center for Orbit Determination in Europe and GFZ [41]. Additionally, GFZ's GBM products have been widely adopted for the evaluation of real-time orbit and clock products [36; 42]. The differential code bias (DCB) for BDS-3 from the PPP-B2b service was assessed using data from the German Aerospace Center (DLR) and the Chinese Academy of Sciences (CAS). The ZTD values estimated with the PPP-B2b and Centre National d'Etudes Spatiales (CNES) real-time streams are investigated via comparison with those derived from the final clock and orbit products retrieved from the GBM and ZTD data provided by the IGS. Because it is a well-established method to estimate ZTD/PWV using RTS services, such as CNES RTS, comparing the performance of CNES and PPP-B2b allows us to evaluate the level of accuracy PPP-B2b currently achieves for the real-time applications. As indicated by [PERSON] et al. [43], the orbit accuracy of GNSS products for GPS has been reported to be better than 5 cm in all three directions, with clock errors under 0.1 ns. For BDS, the orbit accuracy is approximately 10 cm, with clock errors around 0.66 ns. The latency of these products is approximately 18 s. The GNSS-derived ZTD and PWV data are compared with those determined from the European Centre for Medium-Range Weather Forecasting (ECMWF) Reanalysis fifth generation (ERA5) and radiosonde observations from the Integrated Global Radiosonde Archive (IGRA). Radiosonde data offer high accuracy through direct atmospheric measurements but are spatially and temporally limited. ERA5, though model-based, provides continuous global coverage and high temporal resolution.