The Contribution Of Residential Coal Combustion To PM_2.5 Pollution Over China's Beijing-tianjin-hebei Region In Winter

With the rapid development of economy and the acceleration of urbanization,Beijing-Tianjin-Hebei?BTH?region experiences serve haze events all through the year,especially in the winter heating season.Seven of the cities in this region were among China's ten most polluted in 2015.Residential coal,as the major energy for households in China,with a high coverage and emission factor,has increasing been cited as a possible source for the PM_2.5 pollution that causes the haze episodes,which is worthy of attention.In this work,to quantify the contribution of BTH's residential coal combustion to PM_2.5 levels in winter,a WRF-CMAQ modeling system was applied to simulate the regional haze pollution during December 2015.Four WRF schemes?FNL+ACM2,FNL+YSU,ERA-Interim+ACM2,ERA-Interim+YSU?were compared to get the best meteorological scheme.Then,several emission scenarios were designed to study the contribution from both regional and city scales.The main conclusions are as followings:The performance of meteorological model showed ERA-Interim+ACM2 schemes gave the best meteorological results with reasonable values for MB and NMB,the highest correlation coefficient,and the smallest values of ME,NME and RMSE.The WRF-CMAQ model reproduced the high concentrations centered over the plains of Hebei Province to the South of the Yan Mountains and the East of the Taihang Mountains,and most haze episodes for cities in the BTH region observed during December 2015.The contribution of residential coal combustion to ambient pollution in the BTH area was qualified using the Brute Force approach.Residential coal combustion was found to contribute significantly to the high PM_2.5 concentrations,representing nearly half?46%?of the regional monthly average.Of this total,Beijing and Tianjin contributed 3%each while households in Hebei Province contributed 40%.For Beijing,residential coal combustion in the BTH area contributed 49%to the monthly averaged PM_2.5 concentration,29%of which was from Beijing,18%from Hebei Province and 2%was from Tianjin.In Tianjin,residential coal combustion contributed 48%of the total PM_2.5 emissions with 24%from Hebei Province,20%from Tianjin and 4%from Beijing.For cities in Hebei Province the contribution to total emissions from household coal combustion in the BTH area varied from 22-58%,with those in southern plains much more affected than cities in the northern mountainous and plateau regions.Langfang was the most affected city.During haze episodes,residential coal combustion in the BTH area contributed 30-57%of the average PM_2.5 concentration across the haze episode when viewed at a regional level,and 15-65%when viewed at the city-scale.The decrease of coal consumption could effectively inhibit the growth and peak of PM_2.5 concentrations in the night.The fact that the PM_2.5 concentration in Beijing and Tianjin was strongly affected by residential coal combustion in Hebei Province suggests that regional efforts to control emissions are necessary to improve air quality in these megacities.Based on the simulation results and considering the current situation of residential coal usage,efforts can be made from replacing with clean coals,phasing out the use of unsuitable stoves,promoting central heating and energy-efficient building,or even better replacing with clean energy to deal with the air pollution caused by residential coal combustion,and eventually realize the complete replacement of residential coal use.