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We used the WRF-Chem model to simulate the surface PM2.5 concentrations over the Northern China Plain (NCP) during a severe haze event between December 6 and 10, 2015, with the goal of assessing the effectiveness of the emergency response measures (ERMs) implemented during this period to alleviate the haze pollution. We estimated that, with the exception of NH3, anthropogenic pollutant emissions were significantly reduced by 8% to 48% over the NCP during December 6 to 10 as a result of the ERM-implementation. Our simulations using the reduced anthropogenic emissions reproduced the observed PM2.5 concentrations and compositions over the NCP during the severe haze event. During the haze event, stagnant regional meteorological conditions led to a lengthening of the PM2.5 lifetime in the NCP boundary layer to 5 days, compared to a 1-day lifetime during the preceeding clean period. During the severe haze event, only approximately 20% of the surface PM2.5 in Beijing was attributable to local emissions, while more than 62% of the surface PM2.5 in the rest of NCP was attributable to local emissions. We found that the effects of the implemented ERMs to be modest, reducing the mean surface PM2.5 concentrations during the polluted period by 7% in Beijing and by 4% for the rest of the NCP. This modest effect was because the duration of the ERM enforcement was much shorter than the lifetime of PM2.5 during the haze event, such that there was insufficient time for the PM2.5 concentrations to fully reflect the reduction in emissions. We conclude that anthropogenic emissions in the NCP during severe wintertime haze events would have to be reduced by a much larger percentage if more pronounced abatement of PM2.5 concentrations were desired.

Emergency Response Measures to Alleviate a Severe Haze Pollution Event in Northern China during December 2015: Assessment of Effectiveness