The spatial-temporal variation of biomass burning in June during the wheat harvestseason in the North China(32-41°N,111-120°E)and its influence on the regional aerosol opticaldepth(AOD)and the chemical compositions of size-segregated aerosols in the urban environmentwere investigated to evaluate the effectiveness of the burn ban policy and the influence on regionalpollution.Fire events that occurred in early and middle June accounted for approximately 89%ofthe events during the month,and fire points located in mid-eastern China(32.5-35.5°N,114-120°E)comprised 71%.The occurrences exhibit oscillatory changes with a minimum in 2008(during the Beijing Olympics)and a peak and explosive growth in 2012.Under high relativehumidity and south winds,fire emissions from straw burning combined with high urban/industrialemissions to produce intensive regional haze pollution in the North Plain.The formation ofsecondary inorganic particles was intensified due to the interactions of smoke plumes andurban/industrial pollutants in an urban environment.Higher concentrations and percentages(79%)of sulfate,nitrate,ammonium,and organic carbon in the fine particles under high relativehumidity conditions contributed to a deteriorated urban visibility.Therefore,stronger managementand a comprehensive ban on wheat straw burning in June are urgently needed,especially duringyears when the south wind is dominant.