| Qingdao is a significant channel for the transport of aerosols from the Asian continent to the North Pacific.It is also an important coastal central city and an international port city.The air pollutants in Qingdao are affected by both the ocean and continent.Qingdao suffers from more severe air pollution than other coastal cities in China.Compared with coarse particles,PMi and PM2.5 play a more important role on the formation of haze and human health.Currently,PMi and PM2.5 have constrained the improvement of the air quality in urban.Therefore,it is essential to study the chemical compositions in PM1 and PM2.5 in Qingdao.In our study,the 11.5-h PM1 and PM2.5 samples were collected in January and July 2019 at a background site(near the coastline)and an urban site(18 km away from the coastline)in Qingdao to analyze water-soluble inorganic ions(WSIIs),organic carbon(OC)and elemental carbon(EC).PM2.5 samples were collected at the background site and urban site in July 2019 for the analysis of inorganic element.The spatial and temporal variations,sources and health risk of the chemical compositions were synthetically explored in our study.The results showed that the average concentrations of total water-soluble ions(∑WSIIs)at background site and urban site were 18.74 ± 13.06 and 24.37 ± 15.16μg m-3 in PMi,and 29.00±25.16 and 35.28 ± 30.50 μg m-3 in PM2.5,respectively.The average concentrations of OC and EC at background site and urban site were 7.14±6.14,1.83 ± 1.68,11.80 ± 11.09 and 2.77 ± 2.71 μg m-3 in PMi,9.27 ± 8.65,2.36±2.29,14.65 ±13.83 and 3.85±3.89 μg m-3 in PM2.5.The spatial and seasonal variations of∑WSIIs,OC and EC were shown as:urban site>background site and winter>summer.∑WSIIs,OC and EC in PMi accounted for 78.7%-93.7%of WSIIs,OC and EC in PM2.5 in summer,higher than that in winter(68.0%-78.8%).SO42-,NO3-and NH4+were the major components in EWSIis.The existence forms of SO42-,NO3-and NH4+in winter were(NH4)2SO4 and NH4NO3 and in summer were NH4HSO4 and NH4NO3.During summer period,the concentrations of sea salt presented significantly difference(p<0.05)between PMi and PM2.5(PM2.5>PMi),background site and urban site(background site>urban site)and daytime and nighttime(daytime>nighttime).Positive matrix factorization model(PMF)indicated secondary inorganic aerosols(31.13%),biomass burning(28.98%),aged sea salt(21.60%),coal combustion(10.91%)and crustal dust(7.39%)were major sources of WSIIs,OC and EC.Coal and biomass burning sources played more obvious roles on urban site but secondary inorganic aerosols and aged sea salt made more apparent contributions at background site.The contribution of aged sea salt source was significantly increased from winter to summer.While the contributions of secondary inorganic aerosols,biomass burning,coal combustion and crustal dust were decreased.Concentration weighted trajectories model(CWT)implied Shandong Province and Bohai Sea were the important source regions for secondary inorganic aerosols and coal combustion;Shandong,Hebei,Northern Henan and Bohai Sea were major source regions for biomass burning source;the potential source regions of aged sea salt were Yellow Sea,Shandong,Jiangsu and Anhui Provinces;Western Shandong Province was dominate source region for crustal dust.The total concentration of PM2.5-bound inorganic elements at background site was 1258.35±1033.43 ng m-3,significantly lower than that at urban site(1699.27±808.53 ng m-3).The health risk assessments for toxic elements implied that the total non-carcinogenic risks via inhalation can be ignored and the total carcinogenic risks were within acceptable risk level.Principal component analysis(PCA)indicated inorganic elements were mainly produced from industrial production,fossil fuel combustion,traffic emissions,and soil/road dust.Sea salt was also a source for inorganic elements in the background site.The Yellow Sea,Jiangsu,Anhui and Eastern Shandong were the main sources regions of inorganic elements. |
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