title: Positive matrix factorization of a 32-month series of daily PM2.5speciation data with incorporation of temperature stratification.
abstract: This study presents source apportionment results for PM2.5from applying positive matrix factorization (PMF) to a 32-month series of daily PM2.5compositional data from Denver, CO, including concentrations of sulfate, nitrate, bulk elemental carbon (EC) and organic carbon (OC), and 51 organic molecular markers (OMMs). An optimum 8-factor solution was determined primarily based on the interpretability of the PMF results and rate of matching factors from bootstrapped PMF solutions with those from the base case solution. These eight factors were identified as inorganic ion,n-alkane, EC/sterane, lightn-alkane/polycyclic aromatic hydrocarbon (PAH), medium alkane/alkanoic acid, PAH, winter/methoxyphenol and summer/oddn-alkane. The inorganic ion factor dominated the reconstructed PM2.5mass (sulfate + nitrate + EC + OC) in cold periods (daily average temperature < 10 °C; 43.7% of reconstructed PM2.5mass) whereas the summer/oddn-alkane factor dominated in hot periods (> 20 °C; 53.1%). The two factors had comparable relative contributions of 26.5% and 27.1% in warm periods with temperatures between 10 °C and 20 °C. Each of the seven factors resolved in a previous study (Dutton et al., 2010b) using a 1-year data set from the same location matches one factor from the current work based on comparing factor profiles. Six out of the seven matched pairs of factors are linked to similar source classes as suggested by the strong correlations between factor contributions (r= 0.89 - 0.98). Temperature-stratified source apportionment was conducted for three subsets of the data in the current study, corresponding to the cold, warm and hot periods mentioned above. The cold period (7-factor) solution exhibited a similar distribution of reconstructed PM2.5mass as the full data set solution. The factor contributions of the warm period (7-factor) solution were well correlated with those from the full data set solution (r= 0.76 - 0.99). However, the reconstructed PM2.5mass was distributed more to inorganic ion,n-alkane and medium alkane/alkanoic acid factors in the warm period solution than in the full data set solution. For the hot period (6-factor) solution, PM2.5mass distribution was quite different from that of the full data set solution, as illustrated by regression slopes as low as 0.2 and as high as 4.8 of each matched pair of factors across the two solutions.
authors.affiliation: Department of Mechanical Engineering, College of Engineering and Applied Science, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Mingjie
authors.initials: M
authors.lastname: Xie
authors.affiliation: Department of Mechanical Engineering, College of Engineering and Applied Science, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Ricardo
authors.initials: R
authors.lastname: Piedrahita
authors.affiliation: National Center for Environmental Assessment, U.S. Environmental Protection Agency, Research Triangle Park, NC 27711, USA.
authors.forename: Steven J
authors.initials: SJ
authors.lastname: Dutton
authors.affiliation: Department of Mechanical Engineering, College of Engineering and Applied Science, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Jana B
authors.initials: JB
authors.lastname: Milford
authors.affiliation: Department of Mechanical Engineering, College of Engineering and Applied Science, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Joshua G
authors.initials: JG
authors.lastname: Hemann
authors.affiliation: Department of Environmental and Radiological Health Sciences, Colorado State University, Fort Collins, CO 80523, USA.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Peel
authors.affiliation: Department of Mechanical Engineering, College of Engineering and Applied Science, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Shelly L
authors.initials: SL
authors.lastname: Miller
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, School of Public Health, University of Washington, Seattle, WA 98195, USA.
authors.forename: Sun-Young
authors.initials: SY
authors.lastname: Kim
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, School of Public Health, University of Washington, Seattle, WA 98195, USA.
authors.forename: Sverre
authors.initials: S
authors.lastname: Vedal
authors.affiliation: Department of Environmental and Occupational Health Sciences, University of Washington, School of Public Health, University of Washington, Seattle, WA 98195, USA.
authors.forename: Lianne
authors.initials: L
authors.lastname: Sheppard
authors.affiliation: Department of Mechanical Engineering, College of Engineering and Applied Science, University of Colorado, Boulder, CO 80309, USA.
authors.forename: Michael P
authors.initials: MP
authors.lastname: Hannigan
keywords: Organic molecular markers; Positive matrix factorization; Reconstructed PM2.5 mass; Source apportionment; Temperature-stratified