Real neutralization reactions of amines against ammonia by acids in ambient air

Amines reportedly overwhelm ammonia in generating new particles through neutralizing sulfuric acid vapor even with several orders smaller concentrations of amines against ammonia in ambient air, demonstrating an attractive prospect in adjusting concentrations of amines to adjust aerosol number loadings, alleviate air pollution and manipulate aerosol cooling effects. Due to lack of in-situ observations, real competition of amines against ammonia in ambient air to be neutralized by acids remains poorly understood. Here, successful semi-continuous measurements of gaseous amines and ammonia and their particulate partners in marine atmospheres reveal that atmospheric trimethylamine (TMA_gas) unable to compete with NH_3gas and to form particulate trimethylaminium (TMAH⁺), but the particulate TMA (TMA_particulate) is detectable and comparable to TMA_gas under NH_3gas <1.0 µg m^-3. Contradictory to the common knowledge, the preexisting TMA_particulate is largely depleted in strong SO₂ plumes with abundant acids and even depleted NH_3gas. A two-aerosol-phase transfer concept model is proposed to interpret the new findings, but no single-phase acid-base neutralization reactions can. In contrast, observational evidences confirm that gaseous dimethylamine (DMA_gas) plus particulate dimethylaminium (DMAH⁺) overwhelmingly exist as DMAH⁺ under atmospheric NH₃ (NH_3gas) <0.3 µg m^-3 versus DMA_gas under NH_3gas >1.8 µg m^-3, respectively. The neutralization of DMA_gas to form DMAH⁺ is always enhanced in strong SO₂ plumes, almost independent on NH_3gas. Thermodynamically, DMA_gas may act as a competitor in generating secondary particles only under low NH_3gas or in SO₂ plumes.