Source apportionment of PM2.5 using online and offline measurements of chemical components in Tianjin, China

PM2.5 and chemical species of water-soluble inorganic ions, carbon components as well as elements were simultaneously measured by online and offline methods in Tianjin, China. Online measured PM2.5, total carbon, and major ions showed good agreement with offline results (r > 0.7), while obvious differences were found for most elements with correlation coefficients lower than 0.6. Online measured ions and most elements (except As, Ca, Ni) showed higher or comparable estimated annual average concentrations than offline results. Sources of PM2.5 were identified by using Positive Matrix Factorization (PMF) model respectively with online and offline data. Higher contributions of secondary source (38%) and secondary sulfate (11%) for online method could be partly caused by higher concentrations of SO42- and NO3- compared to offline method (30%, 10%). Lower source contribution of dust for online (4%) method might partly relate to lower concentration of Ca compared to offline measurement (7%). Different source contribution estimates of vehicle emission and coal combustion between online (18%, 24%) and offline (21%, 25%) may be partly linked to variation of concentrations of OC and EC resulted from different analytical methods. Industrial source, and sea salt & biomass burning showed lower source contributions both online (4%, 1%) and offline (5%, 2%).

Automated summary

Online and offline measurements in Tianjin, China showed good agreement for PM2.5 and major ions, but significant differences were found in element concentrations, possibly due to different analytical methods. Source contributions of PM2.5 were identified using Positive Matrix Factorization models with online and offline data.