Particle formation at a continental background site: comparison of model results with observations

At Hohenpeissenberg (47◦48′N, 11◦07′ E, 988 m asl), a rural site 200 300 m higher than the surrounding terrain, sulphuric acid concentrations, particle size distributions, and other trace gas concentrations were measured over a two and a half year period. Measured particle number concentrations and inferred particle surface area concen5 trations were compared with box-model simulations based on a multimodal lognormal aerosol module that included a binary sulphuric acid water nucleation scheme. The calculated nucleation rates were corrected with a factor to match measured particle number concentrations. These corrections varied over a range of 10−3−1017. The correction factors were close to 1 for the measurements made in the winter, which repre10 sented stable thermal stratification and low wind conditions. In contrast, the correction factors were the largest for measurements made under strong convective conditions. Our comparison of measured and simulated particle size distributions suggest a distant particle-formation process under convective conditions near the interface of the mixed layer and the entrainment zone, followed by downward transport and particle 15 growth. For stable stratification and low winds, our comparisons suggest that particles formed close to the measurement site.