10th International Aerosol Conference September 2 - September 7, 2018 America's Center Convention Complex St. Louis, Missouri, USA
Abstract View
Thermodynamics of Neutral Ternary (H2SO4-H2O-NH3) New Particle Formation Derived from CLOUD Chamber Measurements
ANDREAS KÜRTEN, Goethe University, Frankfurt
Abstract Number: 706 Working Group: Aerosol Chemistry
Abstract Ammonia is an important atmospheric trace gas that is responsible for the formation of a large fraction of secondary aerosol. The largest source of ammonia is anthropogenic emissions. Recently, it was estimated that eliminating agricultural emissions of ammonia could reduce PM2.5 by up to 50% over large regions of Europe (Pozzer et al., 2017). Regarding the number concentration of aerosol particles and cloud condensation nuclei (CCN), ammonia is also important as it can efficiently enhance new particle formation (NPF) due to an acid-base stabilization mechanism together with sulfuric acid (Kirkby et al., 2011).
New particle formation rates from several hundred CLOUD chamber measurements were recently used to parameterize NPF rates as a function of sulfuric acid, ammonia, and ion concentration over a wide range of temperatures (~208 to 298 K) (Dunne et al., 2016). The implementation of this parameterization was used in the GLOMAP (Global Model of Aerosol Processes) model to estimate the contribution of individual nucleation channels (e.g., binary neutral, ternary neutral, etc.) to global aerosol and CCN formation. These simulations indicate that more than half of all particle formation in the troposphere involves ammonia. Kürten et al. (2016) also highlighted the strong enhancement of ammonia on NPF, even when ammonia was present at tiny mixing ratios (pptv-range). However, the reported parameterization by Dunne et al. (2016) does not give any insight into the thermodynamics (i.e., the evaporation rates) of the nucleating sulfuric acid-ammonia clusters. Evaporation rates reported in the literature are mainly based on quantum chemical calculations, with rare exceptions (e.g., Hanson et al., 2017).
Here we use the CLOUD NPF rates from Dunne et al. (2016) and Kürten et al. (2016) to derive the evaporation rates for the most important nucleating clusters. We use an acid-base scheme in the nucleation and growth model that was recently introduced by Kürten et al. (2018). The evaporation rates are determined by minimizing the average error between modeled and measured NPF rates. Applying this method over a wide range of experimental conditions (temperature, ammonia and sulfuric acid concentrations), the evaporation rates for the smallest sulfuric acid-ammonia clusters can be determined (up to the tetramer containing four sulfuric acid and four ammonia molecules).
The results of this study will be reported and the derived thermodynamic data will be compared to literature values. In addition, further model results will be discussed, e.g., the influence of the condensation sink on new particle formation and growth can be tested, as well as the influence of ammonia on the growth rates of particles.
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