4:45 PM - 5:00 PM
[AAS21-29] Major ion composition in aerosol: As an new indicator of chlorine deficiency
Keywords:atmospheric chemistry, aerosol, Na, XAFS spectroscopy
Size-fractionated aerosol particles on land were collected by a high volume cascade impactor at Higashi-Hiroshima from December 2012 to March 2014. Marine total suspended particulate (TSP) and size-fractionated aerosol particles were collected in the R/V Hakuho-Maru research cruises of KH-12-4 (the North Pacific Ocean: from 23th August to 3rd October 2012) and KH-13-4 Leg. 4 (the Bay of Bengal: from 31th July to 14th August 2013), respectively. Major ionic concentrations (Na+, NH4+, K+, Mg2+, Ca2+, Cl-, NO3- and SO42-) in aerosol samples were determined by an ion chromatography after appropriate pretreatment. MF parameters were calculated as [X]eq/[total anion]eq (X: Cl-, NO3- and nssSO42-). Direct speciation of Na in continental size-fractionated aerosol particles were conducted by XAFS spectroscopy on BL-10, SR-center, Ritsumeikan University.
MF[Cl-]eq was inversely correlated with both MF[NO3-]eq and MF[nssSO42-]eq in continental coarse aerosol particles. It can be said that the chlorine deficiency is explained by the reaction with NO3- and/or nssSO42-. The regression line for MF[Cl-]eq-MF[nssSO42-]eq was -2.16. As for MF[Cl-]eq-MF[NO3-]eq, the regression line shows -1.03, and this regression line satisfies the equation of y=1-x. Thus, HNO3 has large contribution as a reactant of NaCl in the urban atmosphere. Furthermore, chemical reaction of NaCl with HNO3 and H2SO4 preferentially occur on the small aerosol particles because further decrement of MF[Cl-]eq was found in smaller size of aerosols compared with that of large aerosol particles. The speciation analysis with XAFS spectroscopy showed comparable results with that obtained from MF analysis using the high reacted aerosol samples from continent (MF[Cl-]eq : MF[NO3-]eq : MF[nssSO42-]eq =18:56:23). As for marine aerosol samples from the North Pacific Ocean, dominant reactant of NaCl is H2SO4. On the other hand, the reaction of NaCl occurs with both NO3- and SO42- above the Bay of Bengal.
As a consequence, MF is very useful tools to find dominant reactant of NaCl and Na chemical species as a result of chlorine deficiency in both continental and marine aerosol particles.