Seasonal differences in observed versus modeled new particle formation over boreal regions

Abstract. Realistic representation of atmospheric aerosol size distribution dynamics in large scale climate models is important for developing accurate descriptions of aerosol-cloud interactions. Despite the dynamic nature of the distributions, which have large seasonal and diurnal changes, model evaluations often focus on the annual median size distribution. Using more comprehensive monthly and diurnal model illustrations can be crucial for evaluating model performance and potential aerosol effects for short term variations. In this study, we assess the impact of a molecular model scheme for NH₃−H₂SO₄ nucleation integrated into the Earth System Model (ESM) EC-Earth3, across different seasons, months, and days within the boreal climate during the year 2018. Measured number size distributions from two in-situ boreal stations are used to evaluate and to study particle formation and growth representation in EC-Earth3 over 2018. Additionally, we utilize results from the ADCHEM model, a state of the art 1-D Lagrangian aerosol-chemistry model. This allows us to compare EC-Earth3 against results from highly detailed model description of aerosol formation and growth at the boreal stations. When comparing diurnal EC-Earth3 model results with ADCHEM and observations, we establish that using solely organic−H₂SO₄ nucleation parameterization will underestimate the aerosol number concentrations. The new added NH₃−H₂SO₄ nucleation parameterization in this study improves the resulting aerosol number concentrations and reproduction of particle formation events with EC-Earth3. However, from March to October, the EC-Earth3 still underestimates particle formation and growth.