Observation And Simulation Of Fine Particulate Matter Pollution Incident During G20 In Hangzhou

The emission control strategy during the 2016 G20 provided a unique opportunity to investigate fine particulate matters in Hangzhou.We measured the size distribution by SMPS at the National Reference Climatological Station in Hangzhou,and used WRF-Chem to simulate Particulate Matters and meteorological data from August 14 to 21,September 2 to 7,and September 16 to 23.We compared the source of fine particulate matters before,during,and after the 2016 G20 emission control strategy.The main conclusions are as follows:(1)Power plant emission reduction of 50%had suppressed the growth of particles and decreased PM1 by 40%and 58%compared to those before and after the control period.Sub-10 nm nanoparticle concentrations declined by 48%and 42%in morning and evening rush hours,respectively,after the implementation of 50%on-road vehicle reduction.100%VOC emission reduction from industrial sectors enforced in the phase 3 period resulted in a 53%reduction of PMO.,concentration.(2)The emission control did not suppress the occurrence of NPF completely.Four typical NPF events occurred out of 7 days in Phase 1 and Phase 2,probably due to low condensation/coagulation sink.This is different from the NPF events after the emission control period when both nucleation precursor and coagulation sink were high.The NPF event was found to be an important source of nanoparticles below 10nm.The PM0.01 peak concentration around 11:00 AM was enhanced on the NPF days by a factor of 4 compared to the non-NPF days.(3)The performance of WRF-Chem is good in the simulation of particulate matters and meteorological data,but the number concentration of modeled PM,and PMO.,is lower than the observation data.The model result shows that the meteorology conditions before the PMO.,episodes were controlled by anticyclone in 850hPa and the sparsity of the isobaric line on the ground sea level pressure field.The Hangzhou and surrounding area were affected by downward flow.The surface wind speed was weak.These conditions were unfavorable for pollutant diffusion.(4)We compared the three PMO.,episodes before,during,and after the G20 emission control strategy.The cause of the three episodes were similar,because of unfavorable diffusion conditions on synoptic scales.PMO.,pollutant can transport between the grid.We also find out that PM0.1 pollutant transport from surrounding area,when we restricted the research region at G20 emission control strategy area.During the three episodes the contribution of local PM0.1 increase from 62.87%-75.22%to 83.52%-87.38%.At the same time,the number concentration of PM0.1 from outer emission control strategy area almost unchanged.Furthermore,the proportion of PM0.1 pollutant slightly reduce during and after the G20 emission control strategy.Therefore,PM0.1 pollutant transport from emission control strategy area led to the three episodes in Hangzhou.(5)Although the strictest emission control scheme was enforced during the Phase 3 period from August 31 to September 6,two PM,episodes were still observed.The model simulation suggested that the two episodes were not resulted from the intrusion of pollutants outside of the emission control region.Instead,the episodes were due to the unfavorable synoptic situations,including the dominance of subsidence airflow,weak wind speed,and weak vertical temperature gradient.Larger particle sizes and enhanced secondary inorganic content were detected in PM1 during the two episodes.