Source apportionment of urban PM_2.5 using positive matrix factorization with vertically distributed measurements of trace elements and nonpolar organic compounds

There are limited source apportionment studies conducted to assess vertical distributions of fine particulate matter (PM_2.5) and its contributing sources in urban regions. Additionally, none of these vertical studies used inorganic and organic tracers simultaneously. The present study aimed to explore the vertical variation of source-specific contributions to PM_2.5 by modeling with both inorganic and organic markers in vertically stratified samples in the Taipei metropolis (Taiwan). One hundred and five samples were collected from three floor-levels at one building and analyzed for trace elements and nonpolar organic compounds (NPOCs). Seven source factors, i.e., industrial emission, biomass burning, PAH related, oil combustion, soil dust, traffic related, and environmental tobacco smoke (ETS)/lubricant, were retrieved by positive matrix factorization (PMF). The major contributors, including industrial emission (29%), biomass burning (23%), and oil combustion (22%), could be involved with regional transported aerosols and showed non-significant variation in the vertical distribution. In contrast, both traffic related and ETS/lubricant factors could be the contributors to the statistically significant difference of PM_2.5 concentrations between floor-levels.