Abstract: To study the influence of emission reduction measures and traffic controls on concentrations of PM_2.5 and distribution of biomass combustion emissions including levoglucosan, sterol and polycyclic aromatic hydrocarbons(PAHs), and evaluate potential risks from biomass combustion, PM_2.5 samples of ambient air in Beijing were collected from August 10 to September 1, 2015(during the military parade to commemorate the Chinese people's Anti-Japanese War and the 70^th anniversary of the world anti-fascist war).The samples were extracted by accelerated solvent extraction system and analyzed by gas chromatography-mass spectrometer.The results showed that the concentrations of PM_2.5 at urban and traffic positions were reduced by 23% and 25% respectively, through emission reduction measures during this period, and that the concentrations of PM_2.5 at urban, traffic and junction positions were reduced by 44%, 45% and 66% respectively, through emission reduction measures and traffic controls.In addition, the emission reduction measures reduced 92.4%-96.1% of levoglucosan.However, beta sitosterol as the other important tracer of biomass combustion and cholesterol as the typical tracer of cooking emission, both reflecting local pollution sources emissions, had no obvious change through emission reduction measures at the three positions.The emission reduction measures had no inhibiting effects on PAHs partly resulting from biomass incomplete combustion.Meanwhile, risk assessment results showed that the biomass combustion emission of PAHs in the urban position, at which levoglucosan was used as the tracer of biomass, was higher than the other two positions, which indicated that the risk of urban position was higher.Therefore, it is important to study biomass combustion emissions and their concentrations during different periods and evaluate the risks, helping formulate reasonable control measures to protect air quality and human health.