Physicochemical Characteristics And Source Analysis Of PM₁ During Autumn And Winter In Qingdao

In recent years,rapid industrialization and urbanization in developing countries have caused severe air pollution.The pollution trajectory of developing countries is similar to that of developed countries.As the world's largest developing country,China has experienced a series of environmental problems The pollution of particulate matter is particularly serious.Using the ZR-3930 instrument,the mass concentration,chemical composition and number concentration of atmospheric PM₁ in autumn and winter of 2017 and 2018 were continuously observed in Qingdao.Combined with the monitoring data of the national control station and the meteorological conditions,the physical and chemical characteristics and sources of atmospheric PM₁ were discussed,and finally the two heavy pollution incidents in November 2018 and January 2019 were analyzed.The main conclusions were:According to the Air Quality Index?AQI?,the observation period was divided into three categories and six levels,one was the air quality condition were excellent and well?AQI is 0 ? 100?,the second were Mild and moderately polluted weather?AQI is 101 ? 200?,and the third category were severe?AQI greater than 200?.In severe and heavily polluted weather,SO₄^2-,NO₃^-,and NH₄⁺ increased respectively 95.62%,288.53%,and 115.55% compared with the first,and 22.05%,98.53%,and 2.65% compared with the second category,indicating the increase in SNA was the reason for the increase in pollution of Qingdao,among which NO₃^-growth was the most obvious.Compared with good weather,Cl-and K+ increased by 64.86% and 100.69% during periods of severe and severe pollution,respectively,indicating that biomass combustion and coal combustion also contributed greatly to the heavy pollution process.The light and moderate pollution phase was mainly affected by biomass combustion,secondary production,coal combustion,and sand-dust,and the third phase was biomass combustion,sea salt,sanddust,secondary production,coal combustion,and motor vehicles.In 2017,first two categories of OC in PM₁,EC were mainly influenced by motor vehicle emissions,and the severe pollution was motor vehicle emissions and household straw burning.During light and moderate pollution in 2018,OC and EC in PM₁ were greatly impacted by vehicle emissions,and others were mainly impacted by coal combustion.From November 21 to December 2,2018,a typical heavy haze-sand pollution process was occurred in Qingdao,which was divided into five stages: pre-haze,haze period,haze-dust mixing period,dust period,and post-dust period.During heavy hazedust pollution,the mass concentration of PM₁ was?40±20??g/m³.In the post-front,the dust air mass kept the air dry and mainly dominated by cold dry dust particles,which was less affected by accumulated anthropogenic pollutants from the areas it passed during long distance transmission.The pre-front was mainly dominated by anthropogenic pollutant air masses from regions with intense emissions,resulting in peak delay 12 h of PM2.5 and PM₁0 in the dust period.During the heavy haze-sand pollution process,the mass concentration of water-soluble ions in PM₁ was?18.53±8.08??g/m³,accounting for?44.32±4.75?% of the mass concentration of PM₁.The SNA mass concentration was?16.67±7.65??g/m³,which accounted for?42.30±4.88?% in PM₁.The SNA in the haze period was 2.17 times that in the sand and dust period.The SOR and NOR in the haze period increased by 28% and 67% respectively than before the haze period,indicating the secondary conversion of NO₃^-in the haze period enhanced significantly.NH₄⁺ in PM₁ mainly existed in the form of?NH4?2SO4 and NH4NO3,when inorganic ions were sufficiently neutralized by ammonium.During the transition of this dust event,air masses passed over of the regions with intense anthropogenic emissions,such as Shanxi,Hebei,northwest of Shandong and so on.When the pre-front arrived in Qingdao,the anthropogenic pollutants thus dominated,which resulted in higher proportions of OC and EC in PM₁ being 1.73 and 1.53 times during the dust period than in the haze period.The SOC/OC values in the haze period and the dust period were 0.43 and 0.48,respectively.The haze period was lower than the sand and dust period,indicating that t the SOC formation during the haze period was suppressed.Heavy pollution in January 2019 was a haze event caused by local pollution sources.During the observation period,the mass concentration of PM₁ was?77.32±20.55??g/m³.The PM₁ mass concentration in the period of light pollution and the period of severe pollution was?64.61±1.13?and?80.49±22.03??g/m³.During the haze pollution,the mass concentration of water-soluble ions were?36.86±10.33??g/m³,accounting for?47.80±4.94?% of the mass concentration of PM₁.The ions were mainly SO₄^2-,and the SOR and NOR values are 0.22,0.10.The NOR values were all greater than 0.1,indicating that the degree of secondary conversion of SO₄^2-and NO₃^-in this pollution process were higher.The mass ratio of [NH₄⁺]/[SO₄^2-] were 4.18,suggesting the atmosphere in this pollution process is ammonia-rich.The SOC/OC of light pollution period and severe pollution period to severe pollution period were 0.63 and 0.56,respectively,indicating that the generation of SOC was inhibited with the increase of pollution degree.Studying the characteristics and sources of PM₁ and its components in autumn and winter in 2017 and 2018,as well as the analysis of typical heavy pollution processes,provide a scientific basis for the potential source area of Qingdao PM₁ and the formulation of autumn and winter pollution countermeasures.