Seasonal variations of biogenic secondary organic aerosol tracers in ambient aerosols from Alaska

We investigated total suspended particles (TSP) collected from central Alaska, USA for molecular compositions of secondary organic aerosol (SOA) derived from the oxidation of biogenic volatile organic compounds (BVOCs). Isoprene-, α-/β-pinene- and β-caryophyllene-SOA tracers were determined using gas chromatography-mass spectrometry. The concentration ranges of isoprene, α-/β-pinene and β-caryophyllene oxidation products were 0.02-18.6 ng m−3 (ave. 4.14 ng m−3), 0.42-8.24 ng m−3 (2.01 ng m−3) and 0.10-9 ng m−3 (1.53 ng m−3), respectively. Isoprene-SOA tracers showed higher concentrations in summer (ave. 8.77 ng m−3), whereas α-/β-pinene- and β-caryophyllene-SOA tracers exhibited highest levels in spring (3.55 ng m−3) and winter (4.04 ng m−3), respectively. β-Caryophyllinic acid and levoglucosan showed a positive correlation, indicating that biomass burning may be a major source for β-caryophyllene. We found that mean contributions of isoprene oxidation products to organic carbon (OC) and water-soluble organic (WSOC) (0.56% and 1.2%, respectively) were higher than those of α-/β-pinene (0.31% and 0.55%) and β-caryophyllene (0.08% and 0.13%). Using a tracer-based method, we estimated the concentrations of secondary organic carbon (SOC) produced from isoprene, α-/β-pinene and β-caryophyllene to be 0.66-718 ngC m−3 (ave. 159 ngC m−3), 7.4-143 ngC m−3 (35 ngC m−3) and 4.5-391 ngC m−3 (66.3 ngC m−3), respectively. Based on SOA tracers, this study suggests that isoprene is a more important precursor for the production of biogenic SOA than α-/β-pinene and β-caryophyllene in subarctic Alaska.