Abstract
Abstract. In this study the homogeneous nucleation rates in the system of sulfuric acid and water were measured by using a flow tube technique. The goal was to directly compare particle formation rates obtained from atmospheric measurements with nucleation rates of freshly nucleated particles measured with particle size magnifier (PSM) which has detection efficiency of unity for particles having mobility diameter of 1.5 nm. The gas phase sulfuric acid concentration in this study was measured with the chemical ionization mass spectrometer (CIMS), commonly used in field measurements. The wall losses of sulfuric acid were estimated from measured concentration profiles along the flow tube. The initial concentrations of sulfuric acid estimated from loss measurements ranged from 108 to 3 × 109 molecules cm−3. The nucleation rates obtained in this study cover about three orders of magnitude from 10−1 to 102 cm−3 s−1 for commercial ultrafine condensation particle counter (UCPC) TSI model 3025A and from 101 to 104 cm−3 s−1 for PSM. The nucleation rates and the slopes (dlnJ/dln [H2SO4]) show satisfactory agreement when compared to empirical kinetic and activation models and the latest atmospheric nucleation data. To the best of our knowledge, this is the first experimental work providing temperature dependent nucleation rate measurements using a high efficiency particle counter with a cut-off-size of 1.5 nm together with direct measurements of gas phase sulfuric acid concentration.
Highlights
Atmospheric new particle formation consists of rather complicated sets of processes, the first of them is gas-to-particle nucleation
The main reason why we focused on obtaining initial sulfuric acid concentration in our flow tube was that the concentration of prepared solution of sulfuric acid and water is known for each particular experiment and the initial sulfuric acid concentration determined with chemical ionization mass spectrometer (CIMS) and ion chromatography (IC) method can be mutually compared
The biggest difference in counting between ultrafine condensation particle counter (UCPC) TSI 3025A and particle size magnifier (PSM) is at lowest nucleation rates, about a factor of 200, and the smallest difference is at highest nucleation rates, about a factor of 3
Summary
Atmospheric new particle formation consists of rather complicated sets of processes, the first of them is gas-to-particle nucleation. In atmospheric measurements and in a laboratory studies (Sipilaet al., 2010; Berndt et al, 2010) it was observed that particle number concentration followed a power-law dependency of about 1–2, compared to CNT prediction that suggest exponents from 4 to 9 (Vehkamaki et al, 2002). This discrepancy has been puzzling to atmospheric researchers for more than a decade. The first in-situ atmospheric measurements of sulfuric acid in troposphere by using chemical ionization mass spectrometer
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