Abstract
Abstract. The aerosol mass spectrometer (AMS), combined with statistical methods such as positive matrix factorization (PMF), has greatly advanced the quantification of primary organic aerosol (POA) sources and total secondary organic aerosol (SOA) mass. However, the use of thermal vaporization and electron ionization yields extensive thermal decomposition and ionization-induced fragmentation, which limit chemical information needed for SOA source apportionment. The recently developed extractive electrospray ionization time-of-flight mass spectrometer (EESI-TOF) provides mass spectra of the organic aerosol fraction with a linear response to mass and no thermal decomposition or ionization-induced fragmentation. However, the costs and operational requirements of online instruments make their use impractical for long-term or spatially dense monitoring applications. This challenge was overcome for AMS measurements by measuring re-nebulized water extracts from ambient filter samples. Here, we apply the same strategy for EESI-TOF measurements of 1 year of 24 h filter samples collected approximately every fourth day throughout 2013 at an urban site. The nebulized water extracts were measured simultaneously with an AMS. The application of positive matrix factorization (PMF) to EESI-TOF spectra resolved seven factors, which describe water-soluble OA: less and more aged biomass burning aerosol (LABBEESI and MABBEESI, respectively), cigarette-smoke-related organic aerosol, primary biological organic aerosol, biogenic secondary organic aerosol, and a summer mixed oxygenated organic aerosol factor. Seasonal trends and relative contributions of the EESI-TOF OA sources were compared with AMS source apportionment factors, measured water-soluble ions, cellulose, and meteorological data. Cluster analysis was utilized to identify key factor-specific ions based on PMF. Both LABB and MABB contribute strongly during winter. LABB is distinguished by very high signals from C6H10O5 (levoglucosan and isomers) and C8H12O6, whereas MABB is characterized by a large number of CxHyOz and CxHyOzN species of two distinct populations: one with low H:C and high O:C and the other with high H:C and low O:C. Two oxygenated summertime SOA sources were attributed to terpene-derived biogenic SOA, a major summertime aerosol source in central Europe. Furthermore, a primary biological organic aerosol factor was identified, which was dominated by plant-derived fatty acids and correlated with free cellulose. The cigarette-smoke-related factor contained a high contribution of nicotine and high abundance of organic nitrate ions with low m∕z.
Highlights
Organic aerosol (OA) has significant but highly uncertain effects on climate and human health (Heal et al, 2012; Kelly et al, 2012)
We summarize the results of the aerosol mass spectrometer (AMS)-positive matrix factorization (PMF) analysis on the watersoluble organic matter (WSOM) fraction, comprising comprised 58 % of the total OM, which as noted in Sect. 2.2 are very similar to those of Daellenbach et al (2017) conducted on different extracts from the same ambient filter samples
A six-factor solution was selected as the best representation for the AMS PMF analysis, yielding factors identified as hydrocarbonlike OA (HOAAMS), cooking OA (COAAMS), biomass burning OA (BBOAAMS), winter oxygenated OA (WOOAAMS), summer oxygenated OA (AMS), and sulfur-containing OA (SCOAAMS)
Summary
Organic aerosol (OA) has significant but highly uncertain effects on climate and human health (Heal et al, 2012; Kelly et al, 2012). Traditional offline techniques like gas chromatography– mass spectrometry (GC-MS) or liquid chromatography– mass spectrometry (LC-MS) are chemically highly specific but measure only a fraction the total organic aerosol. Another solution to this problem is the application of online instrumentation to extracted and re-aerosolized material from particle filter samples routinely collected at ambient monitoring stations (Daellenbach et al, 2016). Drawbacks of the filter sampling and offline measurement strategy include possible positive or negative artifacts due to condensation or evaporation of semi-volatile organics or aging during sampling, while compound-dependent extraction efficiencies make quantification more challenging
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call