A budget analysis of the formation of haze in Beijing

摘要: Abstract During recent winters, hazes often occurred in Beijing, causing major environmental problems. To understand the causes of this “Beijing Haze”, a haze episode (from Oct. 21 to 31, 2013) Beijing was analyzed. episode, daily mean concentration fine particulate matter (PM2.5) reached peak value 270 μg/m3 on 28, 2013, and rapidly decreased 50 μg/m3 next day (Oct. 29, 2013). This strong variability provided good opportunity study Haze”. Two numerical models were applied for study. The first model is chemical/dynamical regional (WRF-Chem). mainly used effects that weather conditions have PM2.5 concentrations region. results show presence high air pressure northwest (NW-High) generally produced winds with clean upwind air. As result, NW-High played an important role cleaning Beijing's PM. However, NW-High's effect did not occur every situation. When there low southeast (SE-Low) accompanied by NW-High, convergent zone appeared Beijing. pollutants became sandwiched, producing second box model, which estimate some crucial parameters associated budget Under calm winds, calculations continuous local emissions accumulate pollutants. 150 μg/m3 250 μg/m3 within one (1) two (2) days, respectively. Without horizontal dilution, can be considered as upper time limit (the fastest time) occurrences events wind speed (WSb) calculated balance between atmospheric processes. WSb strongly dependent planetary boundary layer (PBL) height direction. SE-Low conditions, 2 m/s higher PBL (700 m). under lower heights, increases, reaching 4.5 m/s 7.0 m/s heights 300 m 200 m, In contrast, reduces 2.5 m/s 4.0 m/s. These suggest when prevailing (with speeds >4 m/s), (PM) begins decrease.