Nucleation of particles with sulfuric acid, water, and nitrogeneous bases was studied in a flow reactor. Sulfuric acid and water levels were set by flows over sulfuric acid and water reservoirs, respectively, and the base concentrations were determined from measured permeation rates and flow dilution ratios. Particle number distributions were measured with a nano-differential-mobility-analyzer system. Results indicate that the nucleation capability of NH 3 , methylamine, dimethylamine, and trimethylamine with sulfuric acid increases from NH 3 as the weakest, methylamine next, and dimethylamine and trimethylamine the strongest. Three other bases were studied, and experiments with triethylamine showed that it is less effective than methylamine, and experiments with urea and acetamide showed that their capabilities are much lower than the amines with acetamide having basically no effect. When both NH 3 and an amine were present, nucleation was more strongly enhanced than with just the amine present. Comparisons of nucleation rates to predictions and previous experimental work are discussed, and the sulfuric acid-base nucleation rates measured here are extrapolated to atmospheric conditions. The measurements suggest that atmospheric nucleation rates are significantly affected by synergistic interactions between ammonia and amines.

Nucleation of particles composed of sulfuric acid, water, and nitrogen base molecules was studied using a continuous flow reactor. The particles formed from these vapors were detected with an ultrafine condensation particle counter, while vapors of sulfuric acid and nitrogen bases were detected by chemical ionization mass spectrometry. Variation of particle numbers with sulfuric acid concentration yielded a power dependency on sulfuric acid of 5 ± 1 for relative humidities of 14–68% at 296 K; similar experiments with varying water content yielded power dependencies on H₂O of ~7. The critical cluster contains about 5 H₂SO₄ molecules and a new treatment of the power dependency for H₂O suggests about 12 H₂O molecules for these conditions. Addition of 2-to-45 pptv of ammonia or methyl amine resulted in up to millions of times more particles than in the absence of these compounds. Particle detection capabilities, sulfuric acid and nitrogen base detection, wall losses, and the extent of particle growth are discussed. Results are compared to previous laboratory nucleation studies and they are also discussed in terms of atmospheric nucleation scenarios

Computational fluid dynamics simulations of a flow reactor provided 3D spatial distributions of its temperature and flow profiles and abundances of sulfuric acid, nitrogeneous base, and the acid-base clusters formed from them. Clusters were simulated via their kinetic formation and decomposition involving sulfuric acid and base molecules. Temperature and flow profiles and the base and sulfuric acid distributions are characterized and the latter is compared to mass spectrometer measurements. Concentrations of simulated clusters of sulfuric acid with either NH or dimethylamine were compared to experimentally measured particle concentrations. Cluster thermodynamics were adjusted to better the agreement between simulated and experimental results. Free energies of acid-base clusters derived here are also compared to recent quantum chemistry calculations. Sensitivities to the thermodynamics were explored with a 2D laminar flow simulation and the abundance of large clusters was most sensitive to the thermodynamics of the smallest cluster, consisting of 1 base and 1 acid. Comparisons of this model to the computational fluid dynamics models provide verification of the implemented cluster chemistry. A box model was used to calculate nucleation rates for the conditions of other experimental work, and to provide predictions of nucleation for typical atmospheric conditions.

Abstract. An acid titration method for quantifying amine permeation rates was used to calibrate an Ambient pressure Proton transfer Mass Spectrometer (AmPMS) that monitors ambient amine compounds. The method involves capturing amines entrained in a N2 flow by bubbling it through an acidified solution (~10−5 M HCl), and the amines are quantified via changes in solution pH with time. Home-made permeation tubes had permeation rates (typically tens of pmol s−1) that depended on the type of amine and tubing and on temperature. Calibrations of AmPMS yielded sensitivities for ammonia, methylamine, dimethylamine, and trimethylamine that are close to the sensitivity assuming a gas-kinetic, ion-molecule rate coefficient. The permeation tubes were also designed to deliver a reproducible amount of amine to a flow reactor where nucleation with sulfuric acid was studied. The high proton affinity compound dimethyl sulfoxide (DMSO), linked to oceanic environments, was also studied and AmPMS is highly sensitive to it. AmPMS was deployed recently in two field campaigns and, using these sensitivities, mixing ratios for ammonia and the alkyl amines are derived from the signals. Correlations between these species and with particle formation events are discussed.

Nucleation of particles composed of sulfuric acid, water, and nitrogen base molecules was studied using a continuous flow reactor. The particles formed from these vapors were detected with an ultrafine condensation particle counter, while vapors of sulfuric acid and nitrogen bases were detected by chemical ionization mass spectrometry. Variation of particle numbers with sulfuric acid concentration yielded a power dependency on sulfuric acid of 5 ± 1 for relative humidities of 14–68% at 296 K; similar experiments with varying water content yielded power dependencies on H₂O of ~7. The critical cluster contains about 5 H₂SO₄ molecules and a new treatment of the power dependency for H₂O suggests about 12 H₂O molecules for these conditions. Addition of 2-to-45 pptv of ammonia or methyl amine resulted in up to millions of times more particles than in the absence of these compounds. Particle detection efficiencies, sulfuric acid and nitrogen base detection, wall losses, and the extent of particle growth are discussed with the help of a recent computational fluid dynamics study that simulated the flow and chemistry in the flow reactor. Results are compared to previous laboratory nucleation studies and they are also discussed in terms of atmospheric nucleation scenarios