## 6 Conclusions  
In this study, the accuracy of the BDS-3 and GPS orbit and clock corrections of PPP-B2b was assessed using GBM products from the GFZ as a reference. The DCB for BDS-3 from the PPP-B2b service was assessed using DLR and CAS data. For the period between DOY 069 and DOY 311 in 2022, the comparison between the PPP-B2b clock and GBM clock yielded STD values of 0.16 ns, 0.13 ns, and 0.18 ns for GPS, BDS-3 MEO satellites, and three BDS-3 IGSO satellites, respectively. Regarding the orbit quality, the mean RMSEs for the GPS satellites were 0.08 m, 0.36 m, and 0.28 m in the radial, along-track, and cross-track directions, respectively, which were similar to those of the GPS satellites. For the BDS-3 IGSO satellites, the mean RMSEs in the radial, along-track, and cross-track directions were 0.13 m, 0.37 m, and 0.40 m, respectively, which were slightly worse than those of the BDS-3 MEO and GPS satellites. The differences between the DCB from PPP-B2b and the DCB from DLR or CAS were within \(\pm\)2 ns, and the differences between the DCBs from DLR and CAS were within \(\pm\)1 ns. In terms of the SISREs, BDS-3 performed better than the GPS satellites. The ZTD derived with PPP-B2b and CNES was initially assessed at 32 stations within the region defined by latitude ranging from 38\({}^{\circ}\) S to 48\({}^{\circ}\) N and longitude from 55\({}^{\circ}\) E to 170\({}^{\circ}\) E. This evaluation spanned from Day of Year (DOY) 069 in 2022 to DOY 054 in 2023 and involved comparing the derived ZTD with post-processed ZTD obtained using the GBM clock/orbit and ZTD provided by the IGS. The results highlight a strong dependency of the ZTD accuracy derived with PPP-B2b on the latitude of the stations, whether compared to IGS or GBM ZTD results. When utilizing GBM-derived ZTD as a reference, the mean RMSE of PPP-B2b ZTD is 15.7 mm for nine stations situated between 30\({}^{\circ}\) N and 48\({}^{\circ}\) N. These stations span across diverse locations including northern China (URUM, CHAN, BJ01, and BJFS), Mongolia (ULAB), Uzbekistan (TASH), Japan (USUD), the Republic of Korea (GAMG), and Kyrgyzstan (BIK0). Conversely, for stations positioned between 0\({}^{\circ}\) and 30\({}^{\circ}\) N, and 0\({}^{\circ}\) and 38\({}^{\circ}\) S, the mean RMSE increases to 23.9 mm and 25.0 mm, respectively, significantly higher than that observed between 30\({}^{\circ}\) N and 48\({}^{\circ}\) N. This latitude-dependent pattern of PPP-B2b ZTD remains consistent when compared to the IGS-, ERA5-, and radiosonde-derived ZTD. Additionally, the results indicate that the PPP-B2b service for the MOBS station was rarely applicable at most epochs, with no resolution obtained for more than 70% of the epochs. This limitation arises because the PPP-B2b correction information is derived from tracking stations deployed in China and is intended solely for China and its surrounding areas. Consequently, the performance of PPP-B2b in regions distant from China may degrade due to a reduction in available satellites and a deterioration in satellite geometry. CNES performed much better than PPP-B2b in ZTD estimation, with a mean RMSE of 8.0 mm for 32 stations using GBM-derived ZTD as a reference. The GNSS-derived ZTD/PWV were also compared with those derived from ERA5 and radiosonde. The comparison results reveal that the RMSEs of the GBM-, IGS-, and CNES-derived ZTD and PWV are approximately 20 mm and 3 mm, respectively. For the PPP-B2b solutions, the RMSEs of ZTD and PWV are 27.8 mm and 4.4 mm, respectively, which are worse than those of the IGS, GBM, and CNES solutions. Using the radiosonde-derived ZTD/PWV as a reference, the RMSEs of ZTD and PWV derived with PPP-B2b are 22.4 mm and 3.7 mm, respectively, which are also worse than those of the IGS, GBM, and CNES solutions. The performance of PPP-B2b PWVs also exhibits a strong dependence on location compared to post-processed, ERA-derived, or radiosonde-derived PWVs.