Formation of secondary organic aerosol tracers from anthropogenic and biogenic volatile organic compounds under varied NOx and oxidant conditions

For source apportionment by tracer method of secondary organic aerosol (SOA), the ratios of aerosol tracer to total SOA mass (fSOA) were determined during the oxidation of toluene, naphthalene, α-pinene, and isoprene by a series of laboratory experiments. Seven anthropogenic SOA tracers maintaining an aromatic ring structure, including 4-nitrophthalic acid and 3,5-dinitrosalicylic, were newly investigated as a chamber study together with 21 traditional aerosol tracers of anthropogenic and biogenic SOA. Experiments of the OH-initiated oxidation of anthropogenic VOCs were conducted as a function of the initial VOC/NOx ratio. No significant dependence on the VOC/NOx ratio was observed for the fSOA of 2,3-dihydroxy-4-oxopentanoic acid from toluene and phthalic acid from naphthalene, whereas the fSOA of nitroaromatic compounds such as 5-nitrosalicylic acid, 3,5-dinitrosalicylic acid, and 4-nitrophthalic acid increased with decreasing VOC/NOx ratio. Among seven newly evaluated anthropogenic SOA tracers, we concluded that 3,5-dinitronsalicylic can be used as a toluene SOA tracer, whereas 4-nitrophthalic acid can be used as a naphthalene SOA tracer. Results of kinetic calculations suggest that naphthalene is a major source of 5-nitrosalicylic acid under urban and rural conditions of previous observation studies. The ozonolysis and NO3-initiated oxidation of biogenic VOCs were investigated in addition to OH-initiated oxidation of biogenic VOCs. As for biogenic SOA tracers such as pinic acid and 2-methyltetrols, the fSOA value measured for the NO3-intiated reaction was lower than that of the OH-initiated oxidation and the fSOA value measured for the ozonolysis was not necessarily close to that of the OH-initiated oxidation. These results suggest that daytime and nighttime biogenic SOA formation events are interpreted by using different sets of the fSOA values.