alpha-pinene photooxidation under controlled chemical conditions - Part 2: SOA yield and composition in low- and high-NOx environments

作者：Eddingsaas N C^*; Loza C L; Yee L D; Chan M; Schilling K A; Chhabra P S; Seinfeld J H; Wennberg P O

来源：Atmospheric Chemistry and Physics, 2012, 12(16): 7413-7427.

DOI：10.5194/acp-12-7413-2012

The gas-phase oxidation of alpha-pinene produces a large amount of secondary organic aerosol (SOA) in the atmosphere. A number of carboxylic acids, organosulfates and nitrooxy organosulfates associated with alpha-pinene have been found in field samples and some are used as tracers of alpha-pinene oxidation. alpha-pinene reacts readily with OH and O-3 in the atmosphere followed by reactions with both HO2 and NO. Due to the large number of potential reaction pathways, it can be difficult to determine what conditions lead to SOA. To better understand the SOA yield and chemical composition from low-and high-NOx OH oxidation of alpha-pinene, studies were conducted in the Caltech atmospheric chamber under controlled chemical conditions. Experiments used low O-3 concentrations to ensure that OH was the main oxidant and low alpha-pinene concentrations such that the peroxy radical (RO2) reacted primarily with either HO2 under low-NOx conditions or NO under high-NOx conditions. SOA yield was suppressed under conditions of high-NOx. SOA yield under high-NOx conditions was greater when ammonium sulfate/sulfuric acid seed particles (highly acidic) were present prior to the onset of growth than when ammonium sulfate seed particles (mildly acidic) were present; this dependence was not observed under low-NOx conditions. When aerosol seed particles were introduced after OH oxidation, allowing for later generation species to be exposed to fresh inorganic seed particles, a number of low-NOx products partitioned to the highly acidic aerosol. This indicates that the effect of seed acidity and SOA yield might be under-estimated in traditional experiments where aerosol seed particles are introduced prior to oxidation. We also identify the presence of a number of carboxylic acids that are used as tracer compounds of alpha-pinene oxidation in the field as well as the formation of organosulfates and nitrooxy organosulfates. A number of the carboxylic acids were observed under all conditions, however, pinic and pinonic acid were only observed under low-NOx conditions. Evidence is provided for particle-phase sulfate esterification of multi-functional alcohols.

• 出版日期2012