Abstract
Abstract. The oxidative processing by ozone of the particulate amines octadecylamine (ODA) and hexadecylamine (HDA) is reported. Ozonolysis of these amines resulted in strong NO2– and NO3– ion signals that increased with ozone exposure as monitored by photoelectron resonance capture ionization aerosol mass spectrometry. These products suggest a mechanism of progressive oxidation of the particulate amines to nitroalkanes. Additionally, a strong ion signal at 125 m/z is assigned to the ion NO3– (HNO3). For ozonized mixed particles containing ODA or HDA + oleic acid (OL), with pO3≥3×10–7 atm, imine, secondary amide, and tertiary amide products were measured. These products most likely arise from reactions of amines with aldehydes (for imines) and stabilized Criegee intermediates (SCI) or secondary ozonides (for amides) from the fatty acid. The routes to amides via SCI and/or secondary ozonides were shown to be more important than comparable amide forming reactions between amines and organic acids, using azelaic acid as a test compound. Finally, direct evidence is provided for the formation of a surface barrier in the ODA + OL reaction system that resulted in the retention of OL at high ozone exposures (up to 10−3 atm for 17 s). This effect was not observed in HDA + OL or single component OL particles, suggesting that it may be a species-specific surfactant effect from an in situ generated amide or imine. Implications to tropospheric chemistry, including particle bound amines as sources of oxidized gas phase nitrogen species (e.g.~NO2, NO3), formation of nitrogen enriched HULIS via ozonolysis of amines and source apportionment are discussed.
Highlights
Amines, including aliphatic amines, represent an important contributor to organic nitrogen in the atmosphere and stem from both anthropogenic and biogenic emissions
Two specific goals of this work were to: a) identify chemical classes that may act as particle bound nitrogen sinks and that are representative of oxidatively stressed particulate matter; and b) compare the products formed from heterogeneous ozonolysis of particle bound alkyl amines with gas phase and solution chemistries
The characteristic PERCI AMS profile for ozonized singlecomponent particles consisting of primary, aliphatic amines was initially established under low and high ozone exposures (Fig. 1a, b, respectively)
Summary
Amines, including aliphatic amines, represent an important contributor to organic nitrogen in the atmosphere and stem from both anthropogenic and biogenic emissions. We report on the heterogeneous ozonolysis of two long-chain, primary, aliphatic amines (octadecylamine, ODA; and hexadecylamine, HDA) in single component and mixed fine mode particles These high molecular weight, low-volatility amines were chosen as model systems to minimize particle-to-gas phase partitioning, such that we could study their condensed phase reactivity in the aerosol. Two specific goals of this work were to: a) identify chemical classes that may act as particle bound nitrogen sinks and that are representative of oxidatively stressed particulate matter; and b) compare the products formed from heterogeneous ozonolysis of particle bound alkyl amines with gas phase and solution chemistries From this we hope to begin to better describe the atmospheric aging process of particles rich in organic nitrogen; identify chemical classes that may act potential molecular markers; and elucidate possible routes to nitrogen-rich HULIS formation
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