Effect of NOx level on secondary organic aerosol (SOA)formation from the photooxidation of terpenes

[摘要] Secondary organic aerosol (SOA) formation from the photooxidation of onemonoterpene (α-pinene) and two sesquiterpenes (longifolene andaromadendrene) is investigated in the Caltech environmental chambers. Theeffect of NO_x on SOA formation for these biogenic hydrocarbons isevaluated by performing photooxidation experiments under varying NO_xconditions. The NO_x dependence of α-pinene SOA formationfollows the same trend as that observed previously for a number of SOAprecursors, including isoprene, in which SOA yield (defined as the ratio ofthe mass of organic aerosol formed to the mass of parent hydrocarbonreacted) decreases as NO_x level increases. The NO_x dependence ofSOA yield for the sesquiterpenes, longifolene and aromadendrene, however,differs from that determined for isoprene and α-pinene; the aerosolyield under high-NO_x conditions substantially exceeds that underlow-NO_x conditions. The reversal of the NO_x dependence of SOAformation for the sesquiterpenes is consistent with formation of relativelylow-volatility organic nitrates, and/or the isomerization of large alkoxyradicals leading to less volatile products. Analysis of the aerosol chemicalcomposition for longifolene confirms the presence of organic nitrates underhigh-NO_x conditions. Consequently the formation of SOA from certainbiogenic hydrocarbons such as sesquiterpenes (and possibly largeanthropogenic hydrocarbons as well) may be more efficient in polluted air.

[学科分类] 大气科学