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 (TMAgas) unable to compete with NH3gas and to form particulate trimethylaminium (TMAH+), but the particulate TMA (TMAparticulate) is detectable and comparable to TMAgas under NH3gas <1.0 µg m-3. Contradictory to the common knowledge, the preexisting TMAparticulate is largely depleted in strong SO2 plumes with abundant acids and even depleted NH3gas. 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 (DMAgas) plus particulate dimethylaminium (DMAH+) overwhelmingly exist as DMAH+ under atmospheric NH3 (NH3gas) <0.3 µg m-3 versus DMAgas under NH3gas >1.8 µg m-3, respectively. The neutralization of DMAgas to form DMAH+ is always enhanced in strong SO2 plumes, almost independent on NH3gas. Thermodynamically, DMAgas may act as a competitor in generating secondary particles only under low NH3gas or in SO2 plumes.