PNNL

Abstract

Size-segregated aerosol composition was investigated as part of the Texas 2000 air quality study. The sampling was performed continuously from August 16 to September 15, 2000 at the Williams Tower (62nd floor), Houston, Texas, using a Lundgren type 3-stage impactor (0.07-0.34 microns, 0.34-1.15 microns, and 1.15-2.5 microns cut points). Ex post facto analysis of the collected aerosol was performed using synchrotron x-ray fluorescence (s-XRF) at the Advanced Light Source (ALS) Lawrence Berkeley National Laboratory (LBNL) to yield time series data for many trace elements (Al, Si, S, Ca, Fe, Cl, K, Ti, Mn, Ni, and Cu). A principle component analysis of the data enabled the aerosol to be grouped into three primary types: 1) course mode soil and/or fly ash aerosol (Al, Si, S, Ca, Fe, K, Ti); 2) medium mode soil and/or fly ash aerosol (Al, Si, Ca, Fe, Ti); and 3) sulfur-containing aerosol containing a vanadium-to-nickel ratio of 3.23±1.35 (±2 sigmas). An examination of time series data of element ratios has indicated that the first two aerosol types (Al:Si, Fe:Si, and Ca:Si ratios) may arise from multiple sources, whereas the latter aerosol type (V:S and Ni:S ratios) likely arises from a single source, such as fossil fuel combustion. The three aerosol types above were observed to have mass contributions, respectively, of 18.5%, 14.1%, and 65.8%. The statistical grouping of aerosol type is analyzed further according to air-mass history using classical back-trajectories and enables a source apportionment of the aerosol to be made.