摘要：Effect of four different base compounds [ammonia (NH3), monomethyl- (MMA), dimethyl- (DMA) and trimethylamine (TMA)] on sulphuric-acid–water nucleation was studied using a laminar flow tube. The concentration and size distribution of freshly-formed particles were monitored with an Ultrafine Condensation Particle Counters (UCPC) and a Differential Mobility Particle Sizer (DMPS) system. Two separate experiments were conducted. In the first experiment, the sulphuric acid concentration was measured using a mass spectrometer and the amount of base compound input was determined. In the second experiment, the concentration of base compounds in the flow tube was directly measured with an online ion chromatograph. All experiments were conducted at the constant temperature of 298 K and relative humidity of 30%, as well as constant sulphuric acid concentration. The concentration of the added base compounds was increased stepwise from 27 up to 25 000 pptv. An enhancement of the particle nucleation rate was observed only with TMA, and the maximum enhancement factor (EF) was approximately 5.5 at the TMA concentration of 2500 pptv. The possible nucleation enhancement by the other base substances was most probably saturated due to background contaminant levels of DMA, MMA and NH3. Detection of the base compounds was discussed, and the results obtained in this study were compared with those from other similar laboratory experiments found in literature.
