| In recent years,although the economy in Northeast China(Liaoning,Jilin,and Heilongjiang Provinces)has not increased as rapidly as in other areas,such as the North China Plain.(NCP),Pearl River delta(PRD),and Yangtze River delta(YRD),its air quality deterioration is similar.During the heating period(Northeast China:lasting up to five and a half months,from mid-October to late-March of the next year),air quality index(AQI)in Northeast China is even higher than in other areas.We calculated average annual PM2.5 mass concentration in Northeast China(PM2.5 concentration is relatively low during the non-heating period,the average value is about 30 ?g/m3),and found that it was nearly same as that in developed areas.However,during the heating period,there was a higher number of haze days in Northeast China,and average PM2.5 concentration was approximately 5-6 times higher than that during the non-heating period.Nevertheless,air pollution in Northeast China has not been concerned by scientists and government,therefore,winter haze pollution in Northeast China has not been solved.A field experiment,including PM2.5 and individual particle samples collection,was carried out in central Northeast China from 28 January to 7 February 2015,and a regional haze episode occurred on 1-4 February.The sampling sites are Tongyu observation station(rural site,Tl),Tongyu county(county town site,T2),and Jilin city(urban site,T3),respectively.T1 and T2 are located in rural area,and T3 is located in urban area.OC-EC analysis and ion chromatography were used to analyze organic carbon(OC)/elemental carbon(EC)and water-soluble ions in PM2.5,respectively.Transmission electron microscopy(TEM)and atomic force microscopy(AFM)were used to investigate type,morphology,mixing state,and size distribution of individual particles.Our results showed that organic matter(OM)and secondary inorganic ions(NH4+,SO42-,and NO3-)were dominant in urban PM2.5.In Jilin city,the concentrations of OM,NH4+,SO42-,and NO3-in PM2.5 were 89.5 ?g/m3,24.2 ?g/m3,28.1 ?g/m3,and 32.8 ?g/m3 on the haze days,which were 3.1,2.3,2.7,and 1.4 times higher than that on the non-haze days.Aerosol particles in urban area of Northeast China were divided into five types:organic-rich(the main component was primary organic aerosol(POA)),organic-S,organic-soot,S-fly ash,and S-metal;aerosol particles in rural area of Northeast China were also divided into five types:organic-rich,S-rich,organic-S,K-organic,and organic-soot.In the urban site,the relative abundance of organic-S,S-fly ash,and S-metal particles increased from 39%,1%9 and 1%on the non-haze days to 46%,4%,and 2%on the haze days.The relative abundance of organic-soot and S-rich particles were 3 times and 0.67 times higher in the county town site than in the rural site,respectively.The relative abundance of K-organic particles was 7%in the county town site,which was nearly same as that in the rural site(6%).The size distribution of aerosol particles showed that the peak value in the urban site increased from 249 nm on the non-haze days to 386 nm on the haze days,which can be attributed to the formation of S-rich particles and secondary organic aerosol(SOA)on preexisting particles during the haze period that can increase the particle size.More than 80%of individual particles contained POA(e.g.,dome-like organic,irregular organic,and spherical organic particles)in winter in Northeast China.We indicated that the aerosol particles were mainly from direct emissions of coal burning and biomass burning in rural areas as well as small boilers in urban areas,and?70%of aerosol particles were from inefficient coal burning emissions.We proposed a regional air transports model in winter in Northeast China,which indicated that air pollutants emitted from rural areas can be transported into urban areas under the wintertime monsoon,and further aggravated air pollution in urban areas.We also generated a conceptual model of regional haze formation process.This model indicated that(1)Stable synoptic meteorological conditions drove the haze formation.(2)Household heating and cooking emitted large amounts of POA,and the early stage of haze formation(light or moderate haze)was mainly caused by the enrichment of POA.(3)High levels of SOA,sulfates,and nitrates formation via heterogeneous reactions together with POA accumulation promoted to the evolution from light or moderate to severe haze.We found that compared to hazes in the North China Plain,organic aerosols made a larger contribution to haze formation in Northeast China,and compared to severe hazes over the North China Plain,the PM2.5 in Northeast China contained similar sulfate,higher SOA,and lower nitrate contents.We proposed that the inefficient coal burning activities for household heating and cooking should be controlled in winter in Northeast China. |
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