Abstract
Abstract. A three-dimensional regional chemical transport model (CTM) with detailed aerosol microphysics, PMCAMx-UF, was applied to the European domain to simulate the contribution of direct emissions and secondary formation to total particle number concentrations during May 2008. PMCAMx-UF uses the Dynamic Model for Aerosol Nucleation and the Two-Moment Aerosol Sectional (TOMAS) algorithm to track both aerosol number and mass concentration using a sectional approach. The model predicts nucleation events that occur over scales of hundreds up to thousands of kilometers especially over the Balkans and Southeast Europe. The model predictions were compared against measurements from 7 sites across Europe. The model reproduces more than 70% of the hourly concentrations of particles larger than 10 nm (N10) within a factor of 2. About half of these particles are predicted to originate from nucleation in the lower troposphere. Regional nucleation is predicted to increase the total particle number concentration by approximately a factor of 3. For particles larger than 100 nm the effect varies from an increase of 20% in the eastern Mediterranean to a decrease of 20% in southern Spain and Portugal resulting in a small average increase of around 1% over the whole domain. Nucleation has a significant effect in the predicted N50 levels (up to a factor of 2 increase) mainly in areas where there are condensable vapors to grow the particles to larger sizes. A semi-empirical ternary sulfuric acid-ammonia-water parameterization performs better than the activation or the kinetic parameterizations in reproducing the observations. Reducing emissions of ammonia and sulfur dioxide affects certain parts of the number size distribution.
Highlights
The two major processes that add new particles into the atmosphere are direct emissions and nucleation
The prediction skill of PMCAMx-UF is quantified in terms of the normalized mean bias (NMB), the normalized mean error (NME), and the percent within a factor of 2
PMCAMx-UF, a 3-D regional chemical transport model with detailed aerosol microphysics, was applied to the European domain for the first time, in order to simulate particle number concentrations during the month of May 2008 during which an intensive campaign of measurements was performed in Europe
Summary
The two major processes that add new particles into the atmosphere are direct (primary) emissions and nucleation (secondary particles). Jung et al (2010) simulated in-situ ultrafine particle formation in the sulfate rich area of the Eastern United States and conducted a detailed comparison with data from the Pittsburgh air quality study They found good agreement for particle number concentrations above 3 nm, they stressed the need for more measurement data representative of different environments, and testing of more nucleation parameterizations. Particle size distribution measurements from multiple locations during the same time period are scarce while updated particle number emission inventories for wide areas (such as Europe) that could improve model predictions are rare For these reasons the effect of primary versus secondary contributions to total particle number concentrations on a regional scale is yet to be elucidated. We evaluate the model with surface-based high time resolution measurements from several stations and test different nucleation parameterizations as well as the sensitivity of the model to certain emission changes
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