Organic tracers of fine aerosol particles in central Alaska: summertime composition and sources

Abstract

PM2.5 aerosols were collected at Fairbanks (64.51∘ N and 147.51∘ W) in central Alaska during the summer of 2009 and analyzed for organic tracer compounds using a gas chromatograph–mass spectrometer. The organic compounds were grouped into 14 classes based on their functional groups and sources. Concentrations of the total organics measured ranged from 113 to 1664 ng m−3 (avg 535 ng m−3). Anhydrosugars (avg 186 ng m−3) and n-alkanoic acids (avg 185 ng m−3) were 2 major classes among the 14 compound classes. The similar temporal trends and strong positive correlations among anhydrosugars and n-alkanoic acids demonstrated that biomass burning (BB) is the major source of organic aerosols (OAs) in central Alaska. The dominance of higher molecular weight n-alkanoic acids over lower molecular weight homologs and their carbon preference index (5.6–9.8) confirmed that they were mostly emitted from plant waxes during BB in central Alaska. The mass concentration ratios of levoglucosan to mannosan denoted that softwood is the main biomass burned. The rainfall event distinctly enhanced the levels of mannitol and arabitol due to the growth of fungi and active discharge of fungal spores in the subarctic region. Molecular compositions of biogenic secondary organic aerosol (BSOA) tracers inferred that isoprene is a crucial precursor of BSOA over central Alaska. Our results suggest forest fires and plant emissions to be the crucial factors controlling the levels and molecular composition of OAs in central Alaska. We propose that PM2.5 laden with OAs derived in central Alaska may significantly impact the air quality and climate in the Arctic via long-range atmospheric transport.