Solubility Of Trace Elements In Atmospheric Aerosols And Related Factors In Qingdao, China

Atmospheric aerosol deposition carries nutrients to oceans and some elements canbe the limiting factor of marine primary production (e.g. N, P, Si). Some importanttrace elements could greatly affect marine primary production and carbon sequestration(e.g. Fe) and other trace elements such as Zn and Mn can affect the growth andbiological community structure of marine organisms. For most of these elements,solubility is one of the key factors to determine their bioavailability. Many studies havebeen conducted to study the solubility of trace elements in atmospheric aerosols and theroles of dissolution medium, pH and dissolution time on the solubility has been wellunderstood. However, there is still a huge uncertainty in determine the solubility andwhat is the key factor affecting the solubility is still poorly understood. Compared withsub-Saharan Africa dust, solubility studies of trace elements in Asia dust is verylimited.In this study,119total suspended particulate (TSP) samples were continuouslycollected in December,2012, and January, March and April,2013in Qingdao. Thetotal and soluble concentrations of trace elements were analyzed for investigation oftheir solubility, origins and related factors. We are particularly interested in studyingthe solubility of crustal element such as Fe, Al and Mn and polluted elements such asZn, Pb and Cu. This work is to understand the influence of anthropogenic pollutants onsolubility of trace elements and to service the target for evaluating the impact of Asiandust deposition on marine primary production.Our results show that:1) Fe and Al are the two most abundant trace elements in thecollected aerosol with the average concentration of3817.47ng/m3and3938.50ng/m3,respectively. The concentration of Mn is low with an average of76.12ng/m3. Theaverage concentrations of Zn, Pb and Cuare261.75ng/m3,118.24ng/m3and49.92ng/m3, respectively. With the concentrations in a decreasing order, the remainingelements ranked as Mn> Ba> Sr> Ni> As> V> Rb> Ga> Bi> Cd> Tl> Co> Cs. Whendissolved concentrations of trace elements were considered, the concentration of Znwas the highest, following by Al, Fe, Mn, Pb, Cu, Sr, Ba, As, V, Rb, Ni, Ga, Cd, Tl, Cs,Bi and Co. The solubility of Fe and Al were2.63%and4.60%(on average), respectively and the values were relatively low. In general, the solubility ofanthropogenic elements such as Zn, Cu and As were relatively high and their solubilityreached~25-70%. The solubility of other trace elements also varied a lot, e.g., thelowest one was~10%for Ba and the highest one was~70%for Cs.Principal component analysis showed that the main source of atmosphericaerosols in Qingdao was anthropogenic sources, followed by dust sources and marinesources. Enrichment factor (EFcrust) analysis showed that EFcrustof anthropogenicelements was large and had high solubility, while EFcrustof dust-derived elements wassmall and generally had low solubility. No correlation was obtained between EFcrustandthe solubility of trace elements. According to the HYSPLIT cluster analysis, aerosolsamples can be classified into three groups, i.e.,41.2%samples were mainly affectedby regional transport of anthropogenic pollutants from cities in northern China(AS),26.1%samples were associated with Asian dust invasion (DS) and the remaining32.8%samples were affected by both anthropogenic pollutants and Asian dust(MS). Thesolubility of trace elements in the three groups can be simplified as AS> MS> DS.Trace elements in the three groups had similar EFcrust, indicating that the differences oftrace elements solubility among the three groups were not determined by its originals orchemical composition.Moreover, our results also showed that the solubility of dust-derived elementsdecreased with increasing their total concentration. The reverse was true anthropogenicelements. Significant positive correlation was found between the solubility and surfacearea to volume(S/V) for both of them. The solubility of trace elements appeared to berelated to gravitational settling during their long distance traveling in the atmosphere.According to the air mass trajectory, i.e., AS, DS and MS, the concentration of anions inAS group was1.4times higher than that in DS and MS. The proportion of anions toparticle in mass concentration for AS group was1.7times higher than that in the others.The concentration of soluble trace elements had a significant positive correlation withthat of acid components, suggesting that acidification processes might exert a hugeimpact on the solubility of trace elements.