Experimental particle formation rates spanning tropospheric sulfuric acid and ammonia abundances, ion production rates, and temperatures

Abstract

Binary nucleation of sulfuric acid and water as well as ternary nucleation involving ammonia are thought to be the dominant processes responsible for new particle formation (NPF) in the cold temperatures of the middle and upper troposphere. Ions are also thought to be important for particle nucleation in these regions. However, global models presently lack experimentally measured NPF rates under controlled laboratory conditions and so at present must rely on theoretical or empirical parameterizations. Here with data obtained in the European Organization for Nuclear Research CLOUD (Cosmics Leaving OUtdoor Droplets) chamber, we present the first experimental survey of NPF rates spanning free tropospheric conditions. The conditions during nucleation cover a temperature range from 208 to 298 K, sulfuric acid concentrations between 5 × 10 5 and 1 × 10 9 cm À3 , and ammonia mixing ratios from zero added ammonia, i.e., nominally pure binary, to a maximum of~1400 parts per trillion by volume (pptv). We performed nucleation studies under pure neutral conditions with zero ions being present in the chamber and at ionization rates of up to 75 ion pairs cm À3 s À1 to study neutral and ion-induced nucleation. We found that the contribution from ion-induced nucleation is small at temperatures between 208 and 248 K when ammonia is present at several pptv or higher. However, the presence of charges significantly enhances the nucleation rates, especially at 248 K with zero added ammonia, and for higher temperatures independent of NH 3 levels. We compare these experimental data with calculated cluster formation rates from the Atmospheric Cluster Dynamics Code with cluster evaporation rates obtained from quantum chemistry.

Temperature uniformity in the CERN CLOUD chamber

“…Theoretical considerations and early measurements (Lovejoy, 2004) indicated a strong temperature dependence for the nucleation rates of sulfuric acid particles. This has been confirmed by CLOUD, for example in Kirkby et al (2011) and Kürten et al (2016).…”

Electron-induced chemistry in microhydrated sulfuric acid clusters

“…The temperature-dependent aerosol chamber measurements on the binary H 2 SO 4 -H 2 O nucleation showed that the neutral particle formation is preferred at low temperatures, while ion-induced particle formation dominates at higher temperatures (Duplissy et al, 2016). A significant contribution of the ion-induced nucleation to the sulfuric acid aerosols was observed experimentally using a particle beam under atmospheric conditions (Enghoff et al, 2011).…”

“…However, the ion-induced nucleation alone could not explain the observed nucleation rates (Kirkby et al, 2011). Therefore, other compounds, such as bases (e.g., ammonia and amines) and organic acids, were proposed to contribute to the sulfuric acid aerosol formation (Zhang et al, 2004(Zhang et al, , 2012Kirkby et al, 2011;Almeida et al, 2013;Kürten et al, 2014Kürten et al, , 2016Schobesberger et al, 2015).…”

Influence of temperature on the molecular composition of ions and charged clusters during pure biogenic nucleation

“…Indeed, particle nucleation is dependent on its concentration, albeit with large variability (Kulmala et al, 2004). The combination of sulfuric acid with ammonia and amines increases nucleation rates due to a higher stability of the initial clusters (Almeida et al, 2013;Kirkby et al, 2011;Kürten et al, 2016). However, these clusters alone cannot explain the particle formation rates observed in the atmosphere.…”

“…Kürten et al (2016) studied the effect of temperature on nucleation for the sulfuric-acid-ammonia system, finding that low temperatures decrease the needed concentration of H 2 SO 4 to maintain a certain nucleation rate. Similar results have been found for sulfuric-acid-water binary nucleation Merikanto et al, 2016), where temperatures below 0 • C were needed for NPF to occur at atmospheric concentrations.…”