Points to note:
  • Normally, this web page will be updated daily at around 2 a.m. and 2 p.m.
  • The tool offers at best a qualitative (i.e. not quantitative) assessment, for sand and dust are different from air in terms of their physical characteristics and may not necessarily follow the same trajectory as that for air.
  • The trajectory was prepared using the HYSPLIT model of NOAA. Anyone wishing to quote or further disseminate the data should read the "Disclaimer" of the NOAA Air Resources Laboratory web site for details.
  • Please click here for trajectory of air mass that has reached Hong Kong (without forecast).