Laboratory studies of particle nucleation: Initial results for H₂SO₄, H₂O, and NH₃ vapors

TLDR

The study used a 295 K flow reactor to investigate particle nucleation in H₂SO₄–H₂O vapor, measuring H₂SO₄ concentrations by chemical ionization mass spectrometry and counting new particles with an ultrafine condensation nucleus counter, and examined the effect of adding NH₃ vapor. Particle formation rates were found to scale approximately as [H₂SO₄]⁸ × [H₂O]⁵, differing markedly from prior experiments and theoretical predictions, while trace NH₃ concentrations dramatically enhanced nucleation.

Abstract

Particle formation in the binary H 2 SO 4 ‐ H 2 O vapor system was studied at 295 K in a series of experiments employing a flow reactor. The concentration of H 2 SO 4 was detected by chemical ionization mass spectrometry, and an ultrafine particle condensation nucleus counter was used to count the newly nucleated particles. Results yield a particle formation rate that is approximately proportional to [H 2 SO 4 ] raised to the eighth power and to [H 2 O] raised to the fifth power. The power dependencies measured here are significantly different from those determined in previous experimental work, and furthermore, the water dependence is markedly different from that predicted from current theories. The effect of adding ammonia vapor to the binary system was investigated; concentrations of NH 3 in the many tens of parts per trillion by volume range were observed to promote dramatically the rate of particle nucleation.