Abstract
Abstract. 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.
Highlights
The origin and abundance of particles in the atmosphere have long been studied due to their potential impact on human health and global climate change (IPCC, 2007; Oberdorster et al, 1992; Nel, 2005)
The power dependency (PD1) of the observed number of particles on sulfuric acid concentration have been reported in a number of studies and are compared in Table 2 where the H2SO4 power dependencies along with experimental conditions are listed
A few recent studies report very low values of ∼1.5: the authors (Berndt et al, 2010; Sipilaet al., 2010) speculate that their particle detection efficiency was much better than all earlier work, implying a deficiency in earlier work that hid the low power dependency
Summary
The origin and abundance of particles in the atmosphere have long been studied due to their potential impact on human health and global climate change (IPCC, 2007; Oberdorster et al, 1992; Nel, 2005). Many experiments have been performed within the H2SO4 and H2O system where nucleation rates J and their dependency on sulfuric acid concentration and relative humidity (RH) have been explored. McMurry et al (2000), Kulmala et al (2004), and Kuang et al (2010), have shown that empirical nucleation theories can explain observed boundary-layer atmospheric nucleation rates, one theory with J dependent on sulfuric acid with a power dependency of 1 and the other with 2. Described here are experiments on particle formation based on the Ball et al (1999) techniques They were conducted over a wide range of relative humidity and sulfuric acid concentration at a constant temperature. Ammonia and methyl amine were added to assess their relative enhancing effects on nucleation within the neat H2SO4-H2O system
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