A parameterized method is developed to diagnose the air quality in Beijing and other cities with an index termed (parameters linking air-quality to meteorological elements PLAM) derived from a correlation between PMio and relevant weather elements based on the data between 2000 and 2007.Key weather factors for diagnosing the air pollution intensity are identified and included in PLAM that include atmospheric condensation of water vapour,wet potential equivalent temperature,and wind velocity.It is found that the poor air quality days with elevated PMio are usually associated with higher PLAM values,featuring higher temperature,humidity,lower wind velocity,and higher stability compared to the averaged values in the same period.Both 24 h and 72 h forecasts provided useful services for the day of the opening ceremony of the Beijing Olympic Games and subsequent sport events.A correlation coefficient of 0.82 was achieved between the forecasts and (air pollution index API) and 0.59 between the forecasts and observed PMio,all reaching the significant level of 0.001,for the summer period.A correction factor was also introduced to enable the PLAM to diagnose the observed PMio concentrations all year round.