Physical And Chemical Characteristics,source Apportionment And Health Risk Assessment Of PM₁ In Qingdao During Autumn And Winter

In recent years,with the rapid development of industrialization and urbanization in my country,there are a series of ambient air quality problems in autumn and winter in northern regions,among which particulate matter pollution is particularly serious.A large number of literatures have been reported on fine particulate matter(PM_2.5),but the impact on submicron particulate matter（PM₁）and its chemical components,physicochemical characteristics,sources and human health is still unclear.Regarding the issue above,this study conducted continuous observations of PM₁ in Qingdao during the autumn and winter of 2018,2019 and 2020(hereinafter referred to as OP_2018-2019,OP_2019-2020 and OP_2020-2021),combined with the monitoring data and meteorological data of the state control site.The characteristics,source analysis and health risk assessment of atmospheric PM₁ and its trace elements in autumn and winter in Qingdao were discussed.Through the inter-annual and inter-monthly variation characteristics of PM₁ and its trace elements during OP_2018-2019,OP_2019-2020 and OP_2020-2021,and the pollution characteristics analysis under different air quality levels,the air pollution situation in Qingdao was analyzed.The sources of particulate matter pollution in Qingdao were analyzed by enrichment factor（EF）,positive matrix factoranalysis（PMF）,backward trajectory analysis of airflow（HYSPLIT）and potential source contribution factor（PSCF）.The effects on the ambient air quality of Qingdao under the conditions of sand and dust weather,haze pollution weather and sand dust-haze pollution composite weather were mainly analyzed.In order to further explore the impact of autumn-winter and spring sand-dust weather on Qingdao’s air quality,a sand-dust event observation was conducted in the spring of 2021(hereinafter referred to as SOP₂₀₂₁).Subsequently,based on the U.S.National Environmental Protection Agency（EPA）human health risk assessment model,health risk assessments were conducted on PM₁ for carcinogenic and non-carcinogenic elements in different populations during OP_2018-2019,OP_2019-2020and OP_2020-2021.The main conclusions are:（1）PM1 mass concentrations during OP2018-2019,OP2019-2020 and OP2020-2021 were42.3±24.1,43.6±30.6 and 37.6±24.1μg/m³,respectively.During the observation period,the concentration of particles was positively correlated with particle size.As the particle size increases,the number concentration decreased.Particulate matter was mainly distributed on the accumulation mode（0.10 to 1.00μm）and less distributed on the coarse particle mode（l.00 to l0.0μm）.During the observation period,the total concentration of trace elements decreased steadily,which were 1283±1097,1251±1445and 1223±690 ng/m³,accounting for 3.58±4.79%,3.48±4.42%and 2.86±3.14%of PM₁concentrations,respectively.Compared with OP_2019-2020,the number of Cr,Co,Cu,Zn,Mo,Cd,Ba,Pb and Mn in OP_2020-2021 had increased,which was speculated to be related to the full resumption of work and production during the COVID-19 epidemic and the short-term increased in the contribution of anthropogenic pollution sources.（2）Significant decreases in V and Ni concentrations during OP_2018-2019,OP_2019-2020and OP_2020-2021 were associated with the implementation of the upgraded Domestic Emission Control Area（DECA 2.0）policy for ships.Compared with the pre-policy period,the post-policy V and Ni concentrations decreased by 71.6%and 6.70%,respectively.The SEM results indicate that V and Ni were influenced by ship emission sources and other potential sources of Ni.The V/Ni values decreased by 41.6%after the policy compared to the prepolicy,indicating that Qingdao was significantly influenced by ship sources before the policy was implemented.However,the proposed V/Ni reference values might not serve as a criterion for determining the regional pollution impact of ship emissions since the upgrade of ship fuel from heavy fuel oil to low-sulfur fuel oil in early 2019.（3）The EF values of Pb,As,and Cd in PM₁ during OP_2018-2019,OP_2019-2020 and OP_2020-2021 were all greater than 1000,which were heavily enriched.Five different sources could be resolved using PMF:ship sources,coal combustion/biomass combustion sources,motor vehicle emission sources,industrial emission sources,and crustal sources.Compared with the prepolicy,the relative contribution of ship sources was reduced by 63.5%after the policy.Based on the analysis of the potential source emission areas of V,the potential source areas of V in OP_2019-2020were significantly reduced compared with the OP_2018-2019 period,indicating that the implementation of DECA 2.0 policy has achieved significant results in reducing ship source emissions.（4）Compared with medium-range dust air masses,long-range dust air masses,driven by strong northwesterly winds,had a wide range of influence and long duration in the northern regions of China during OP_2018-2019,OP_2019-2020 and OP_2020-2021.Two staggered events occurred during SOP₂₀₂₁,indicating that the front of the air mass transmission to Qingdao was dominated by anthropogenic pollutant air masses,and the rear of the front was dominated by dust air masses wrapped with large amounts of dust particles.During the SOP₂₀₂₁,PM₁₀,PM_2.5,and PM₁ concentrations were 159±160,50.5±36.5,and 35.4±31.8μg/m³;PM_2.5/PM₁₀ was 0.32,indicating that the particulate matter in Qingdao area was significantly affected by the dusty weather in spring.（5）The carcinogenic risks to the population from Cd,Ni,and Co during OP_2018-2019,OP_2019-2020,and OP_2020-2021 were negligible,and there are carcinogenic risks from Cr and As,but they were still within the acceptable range.The HQ_Mn for children during OP_2019-2020 and OP_2020-2021 when the air quality level was level IV were 1.22 and 1.34,respectively,which exceeded the lower than US EPA standard,indicating that the non-carcinogenic effects of Mn on children should be noted when pollution events occur,and it was recommended to strengthen the control of Mn pollution source emissions.