Abstract:

Based on meteorological and pollutional data, a persistent fog and haze process in Beijing on January 9 to 15, 2013 were diagnosed, and the circulation, meteorological elements, physical quantity field and pollution monitoring status were analyzed. The results indicate that the persistent duration of high PM_2.5 and SO₂ concentrations events exceeds 100 hours, and their concentrations reach a severe pollution level. There are westerly or southwest air flow at upper level, weak warm advection at 850 hPa and inverted trough on surface. They supply favorable background for the persistent fog and haze process. The continuous light fog and haze do not need thicker wet layer and the thickness of wet layer occurring below 925 hPa is sufficient. The thicker wet layer is, the lower visibility is. Maintenance of temperature inversion layer is a main reason for persistent fog and haze. Temperature inversion layer is thin and weak when there is light fog or haze, and its thickness or intensity enlargement is indicative to transition to heavy fog or snow. Weak vorticity advection below 850 hPa is the dynamic condition of persistent light fog or haze. There is a significant dividing line of total temperature advection on 500 hPa, and the height of weaker advection centre is always between 850 hPa and 1000 hPa. The light fog and haze will dissipate when the height of centre reaches 500 hPa.

Key words: Fog and haze, Pollution, Circulation situation, Advection