Particle number concentrations over Europe in 2030: the role of emissions and new particle formation

Abstract. The aerosol particle number concentration is a key parameter when estimating impacts of aerosol particles on climate and human health. We use a three-dimensional chemical transport model with detailed microphysics, PMCAMx-UF, to simulate particle number concentrations over Europe in the year 2030, by applying emission scenarios for trace gases and primary aerosols. The scenarios are based on expected changes in anthropogenic emissions of sulfur dioxide, ammonia, nitrogen oxides, and primary aerosol particles with a diameter less than 2.5 μm (PM_2.5) focusing on a photochemically active period, and the implications for other seasons are discussed.

For the baseline scenario, which represents a best estimate of the evolution of anthropogenic emissions in Europe, PMCAMx-UF predicts that the total particle number concentration (N_tot) will decrease by 30–70% between 2008 and 2030. The number concentration of particles larger than 100 nm (N₁₀₀), a proxy for cloud condensation nuclei (CCN) concentration, is predicted to decrease by 40–70% during the same period. The predicted decrease in N_tot is mainly a result of reduced new particle formation due to the expected reduction in SO₂ emissions, whereas the predicted decrease in N₁₀₀ is a result of both decreasing condensational growth and reduced primary aerosol emissions. For larger emission reductions, PMCAMx-UF predicts reductions of 60–80% in both N_tot and N₁₀₀ over Europe.

Sensitivity tests reveal that a reduction in SO₂ emissions is far more efficient than any other emission reduction investigated, in reducing N_tot. For N₁₀₀, emission reductions of both SO₂ and PM_2.5 contribute significantly to the reduced concentration, even though SO₂ plays the dominant role once more. The impact of SO₂ for both new particle formation and growth over Europe may be expected to be somewhat higher during the simulated period with high photochemical activity than during times of the year with less incoming solar radiation.

The predicted reductions in both N_tot and N₁₀₀ between 2008 and 2030 in this study will likely reduce both the aerosol direct and indirect effects, and limit the damaging effects of aerosol particles on human health in Europe.