Mixed multiway analysis of airborne particle composition data

Abstract

Airborne particle composition data were obtained from week-long samples collected at the northernmost manned site in the world, Alert, Northwest Territories, Canada, during the period from 1980 to 1991. It was found that the measured weekly average concentrations display strong persistent seasonal variations. Initially the measured concentrations of 24 constituents were arranged into both two-way and three-way data arrays, and bilinear and trilinear models were used to fit the data using positive matrix factorization (PMF). Five factors were found to explain the data quite well for both two-way and three-way modeling, and each factor represented a likely particle source. In the two-way modeling the yearly cyclical seasonal variations were not directly retrieved, since the whole 11 years of data were regarded as a single mode in the fitting. In the three-way analysis, fixed seasonality was imposed by assuming the week-to-week patterns of the source contributions to recur from year to year. The factors represent winter Arctic haze, photochemical sulfate after polar sunrise, biogenic sulfur, soil and sea salt. The resulting fit for some elements became worse because the year-to-year variation is not identical for these sources. These results suggested that a mixed two-way and three-way model might be the best representation of the data. The methodology to calculate such a mixed model has just been developed, namely the multilinear engine (ME). In this study the ME has been used to estimate a mixed two-way/three-way model for the Alert aerosol data. Five two-way and two three-way factors have been found to provide the best fit and interpretation of the data. Each factor represents a probable source with a distinctive compositional profile and seasonal variations. The five two-way factors are (i) winter Arctic haze dominated by together with metallic species and peaking from December to March, (ii) soil represented by Si, Al and Ca, (iii) sea salt, (iv) sulfate with high acidity peaking in late March/April, and (v) iodine representing most of the observed I with two maxima, one around September/October and the other around March/April. The two three-way factors are (i) bromine characterized by a maximum in the spring around March/April, and (ii) biogenic sulfur which includes sulfate and methane sulfonate (MSA) with maxima in May and August. The results obtained are consistent with those obtained in the previous study and agree with the current understanding of the Arctic aerosol. In both analyses the year-to-year strength of the biogenic factor appears to correlate strongly with the average temperature in the northern hemisphere. This result suggests that as the temperature rises, there is increased biogenic production of the reduced sulfur precursor compounds that are oxidized in the atmosphere to sulfate and MSA and could be evidence of a negative feedback mechanism in the global climate system that had been previously postulated. Copyright © 1999 John Wiley & Sons, Ltd.