A method for measuring total aerosol oxidative potential (OP) with the dithiothreitol (DTT) assay and comparisons between an urban and roadside site of water-soluble and total OP

摘要

An automated analytical system was developed for measuring theoxidative potential (OP) with the dithiothreitol (DTT) assay of filterextracts that include both water-soluble and water-insoluble (solid) aerosolspecies. Three approaches for measuring total oxidative potential werecompared. These include using methanol as the solvent with (1) andwithout (2) filtering the extract, followed by removing the solvent andreconstituting with water, and (3) extraction in pure water and performingthe OP analysis in the extraction vial with the filter. The water extractionmethod (the third approach, with filter remaining in the vial) generallyyielded the highest DTT responses with better precision (coefficient of variation of 1–5 %) and was correlated with a greater number of other aerosol components. Because no organic solvents were used, which must be mostlyeliminated prior to DTT analysis, it was easiest to automate by modifyingan automated analytical system for measuring water-soluble OP developed byFang et al. (2015). Therefore, the third method was applied to the fieldstudy for the determination of total OP. Daily 23 h filter samples werecollected simultaneously at a roadside (RS) and a representative urban (Georgia Tech, GT)site for two 1-month study periods, and both water-soluble(OP) and total (OP) OPwere measured. Using PM (aerodynamicdiameter    2.5 µm) high-volume samplers with quartz filters,the OP-to-OP ratio atthe urban site was 65 % with a correlation coefficient () of 0.71(  =  35;  value    0.01), compared to a ratio of 62 % and  = 0. 56 (  =  31;  value    0.01) at the roadside site. The same DTT analyses were performed, and similar results were found using particle composition monitors (flow rate of 16.7 L min) with Teflonfilters. Comparison of measurements between sites showed only slightly higherlevels of both OP and OPat the RS site, indicating both OP andOP were largely spatially homogeneous. Theseresults are consistent with roadway emissions as sources of DTT-quantifiedPM OP and indicate that both soluble and insoluble aerosol components contributing to OP are largely secondary.