Abstract
Abstract. Gaseous amines have attracted increasing attention due to their potential role in enhancing particle nucleation and growth and affecting secondary organic aerosol formation. Here we study with a chemistry transport model the global distributions of the most common and abundant amines in the air: monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA). We show that gas phase oxidation and aerosol uptakes are dominant sinks for these methylamines. The oxidation alone (i.e., no aerosol uptake) leads to methylamine lifetimes of 5–10 h in most parts of low and middle latitude regions. The uptake by secondary species with uptake coefficient (γ) of 0.03 (corresponding to the uptake by sulfuric acid particles) reduces the lifetime by ~30% over oceans and much more over the major continents, resulting in a methylamine lifetime of less than 1–2 h over central Europe, eastern Asia, and eastern US. With the estimated global emission flux, from the literature, our simulations indicate that [DMA] in the model surface layer over major continents is generally in the range of 0.1–2 ppt (parts per trillion) when γ = 0.03 and 0.2–10 ppt when γ = 0, and decreases quickly with altitude. [DMA] over oceans is below 0.05 ppt and over polar regions it is below 0.01 ppt. The simulated [MMA] is about a factor of ~2.5 higher while [TMA] is a factor of ~8 higher than [DMA]. The modeled concentrations of methylamines are substantially lower than the limited observed values available, with normalized mean bias ranging from −57 (γ = 0) to −88% (γ = 0.03) for MMA and TMA, and from −78 (γ = 0) to −93% (γ = 0.03) for DMA.
Highlights
The MMA, DMA, and TMA emissions fluxes assumed in the present study (96.2, 38.3, and 196.0 Gg N yr−1, respectively) are 15 % higher, as the same ratios of methylamines to ammonia emission fluxes given in Schade and Crutzen (1995) are used
Depending on the uptake coefficients, [DMA] in the surface layer over major continents is in the range of 0.1–2 ppt when γ = 0.03 (Fig. 2d) and 0.2–10 ppt when γ = 0 (Fig. 2b). [DMA] decreases quickly with altitudes, with zonally averaged values dropping below 0.1 ppt a few hundred meters above the surface (Fig. 3b, d). [DMA] over oceans are below 0.05 ppt and these DMA are emitted from marine organisms (Fig. 1) rather than transported from continents. [DMA] over polar regions is below 0.01 ppt (Figs. 2, 3) due to the lack of emissions there (Fig. 1)
As a result of the substitution by one or more organic functional groups, amines have a stronger basicity than ammonia and may participate in new particle formation in the atmosphere
Summary
Gaseous amines have attracted increasing attention due to theoretical, laboratory, and field measurements indicating that amines may considerably enhance particle formation and growth (Kurtén et al, 2008; Nadykto et al, 2011, 2014; Almeida et al, 2013; Berndt et al, 2010; Zhao et al, 2011; Erupe et al, 2011; Chen et al, 2012; Wang et al, 2010a; Yu et al, 2012) and affect secondary organic aerosol (SOA) formation (De Haan et al, 2009, Myriokefalitakis et al, 2010; Williams et al, 2010). While amines are stronger bases than ammonia and ternary H2SO4-H2O-amine clusters are more stable (Kurtén et al, 2008; Nadykto et al, 2011, 2014; Almeida et al, 2013), the relative role of amines versus ammonia in enhancing particle formation in the atmosphere is yet to be determined (Zollner et al, 2012). This is because the concentration of amines in the atmosphere is generally much lower than that of ammonia (by 2–3 orders of magnitude or more) (Ge et al, 2011a; Hanson et al, 2011). Recent measurements taken during the CLOUD (Cosmics Leaving Outdoor Droplets) chamber experiments at CERN
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