SO<sub>2</sub> oxidation products other than H<sub>2</sub>SO<sub>4</sub> as a trigger of new particle formation. Part 2: Comparison of ambient and laboratory measurements, and atmospheric implications

Abstract

Abstract. Atmospheric new particle formation is generally thought to occur due to homogeneous or ion-induced nucleation of sulphuric acid. We compare ambient nucleation rates with laboratory data from nucleation experiments involving either sulphuric acid or oxidized SO 2 . Atmospheric nucleation occurs at H 2 SO 4 concentrations 2-4 orders of magnitude lower than binary or ternary nucleation rates of H 2 SO 4 produced from a liquid reservoir, and atmospheric H 2 SO 4 concentrations are very well replicated in the SO 2 oxidation experiments. We hypothesize these features to be due to the formation of free HSO 5 radicals in pace with H 2 SO 4 during the SO 2 oxidation. We suggest that at temperatures above ∼250 K these radicals produce nuclei of new aerosols much more efficiently than H 2 SO 4 . These nuclei are activated to further growth by H 2 SO 4 and possibly other trace species. However, at lower temperatures the atmospheric relative acidity is high enough for the H 2 SO 4 -H 2 O nucleation to dominate.

Evidence for the role of organics in aerosol particle formation under atmospheric conditions

“…S8) from the gaseous H 2 SO 4 concentration and compares this with ambient observations from the boreal forest in Hyytiälä, Finland (7). The scatter of the atmospheric nucleation rates is attributed to varying temperature, humidity, or varying contributions of unknown species in the nucleation process (29). Our laboratory data agree surprisingly well with nucleation rates observed in the atmosphere.…”

“…First, a nonlinear regression analysis was applied to our data as suggested by ref. 29. As the nucleation rate may depend on both H 2 SO 4 and NucOrg, Eq.…”

“…However, it only applies when other variables of influence (temperature and gas phase concentrations of other species participating in the nucleation process) remain constant. This restriction is typically neglected because there are not enough data to obtain meaningful correlations at narrow temperature and gas concentration intervals, and most other compounds that might be involved in nucleation are not known (29). Within an individual experiment, H 2 SO 4 and organic photooxidation products are expected to be highly correlated because their formation and loss processes are highly similar.…”

Laboratory study on new particle formation from the reaction OH + SO<sub>2</sub>: influence of experimental conditions, H<sub>2</sub>O vapour, NH<sub>3</sub> and the amine tert-butylamine on the overall process

“…The experimental finding that high NO concentrations can suppress nucleation was taken as an argument supporting the potential role of HSO 5 (Friend et al, 1980;Berndt et al, 2008;Laaksonen et al, 2008). Very recently, Sipilä et al (2010) showed experimentally that with the help of high efficiency particle counters (Sipilä et al, 2009;Vanhanen, 2009) new particle formation can be observed in the laboratory for H 2 SO 4 concentrations down to ∼10 6 molecule cm −3 .…”

Particle formation in the Arctic free troposphere during the ASTAR 2004 campaign: a case study on the influence of vertical motion on the binary homogeneous nucleation of H<sub>2</sub>SO<sub>4</sub>/H<sub>2</sub>O

“…1106 F. Khosrawi et al: Particle nucleation in the Arctic free troposphere ion-mediated or ion-induced nucleation (e.g., Yu and Turco, 2000;Lee et al, 2003;Lovejoy et al, 2004;Curtius et. al., 2006;Laaksonen et al, 2008). Laboratory experiments have suggested that in polluted areas nucleation of new particles may even take place inside clouds through condensation of organic vapors .…”