Abstract
Abstract. Aliphatic amines can form secondary aerosol via oxidation with atmospheric radicals (e.g., hydroxyl radical and nitrate radical). The particle can contain both secondary organic aerosol (SOA) and inorganic salts. The ratio of organic to inorganic materials in the particulate phase influences aerosol hygroscopicity and cloud condensation nuclei (CCN) activity. SOA formed from trimethylamine (TMA) and butylamine (BA) reactions with hydroxyl radical (OH) is composed of organic material of low hygroscopicity (single hygroscopicity parameter, κ, ≤ 0.25). Secondary aerosol formed from the tertiary aliphatic amine (TMA) with N2O5 (source of nitrate radical, NO3) contains less volatile compounds than the primary aliphatic amine (BA) aerosol. As relative humidity (RH) increases, inorganic amine salts are formed as a result of acid–base reactions. The CCN activity of the humid TMA–N2O5 aerosol obeys Zdanovskii, Stokes, and Robinson (ZSR) ideal mixing rules. The humid BA + N2O5 aerosol products were found to be very sensitive to the temperature at which the measurements were made within the streamwise continuous-flow thermal gradient CCN counter; κ ranges from 0.4 to 0.7 dependent on the instrument supersaturation (ss) settings. The variance of the measured aerosol κ values indicates that simple ZSR rules cannot be applied to the CCN results from the primary aliphatic amine system. Overall, aliphatic amine aerosol systems' κ ranges within 0.2 < κ < 0.7. This work indicates that aerosols formed via nighttime reactions with amines are likely to produce hygroscopic and volatile aerosol, whereas photochemical reactions with OH produce secondary organic aerosol of lower CCN activity. The contributions of semivolatile secondary organic and inorganic material from aliphatic amines must be considered for accurate hygroscopicity and CCN predictions from aliphatic amine systems.
Highlights
Atmospheric aerosol can influence climate directly by absorbing and scattering light and indirectly via their ability to act as cloud condensation nuclei (CCN) and influence cloud formation
Nitric acid produced by N2O5 and NO3 can be directly neutralized by TMA and firstgeneration aerosol products to form inorganic salts (Tang et al, 2013)
The CCN activity of the aerosol formed at relative humidity (RH) ∼ 22 % has κ ∼ 0.28 due to the increased εs over the dry experiment, higher than that of the aerosol only composed of organic species
Summary
Atmospheric aerosol can influence climate directly by absorbing and scattering light and indirectly via their ability to act as cloud condensation nuclei (CCN) and influence cloud formation. The relative contribution of inorganic/organic components plays a vital role in the determination of bulk CCN activity of ambient aerosol. X. Tang et al.: Amine aerosol CCN activity sulfate, nitrate, sea salt, and wind-blown dust. Organics make up ∼ 20–90 % of the global aerosol composition in the troposphere (Kanakidou et al, 2005). A small fraction of the organic composition has been speciated and quantified using gas chromatography with mass spectrometry (Finlayson-Pitts and Pitts, 1986; Rogge et al, 1993; Saxena and Hildemann, 1996). Aerosol physical and thermodynamic properties are difficult to predict with little to no information about particle chemical speciation. Parameterizations are used to effectively represent the water uptake potential of atmospheric aerosols
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