Abstract
Abstract. Aerosol forecasts by the European Centre for Medium-Range Weather Forecasts (ECMWF) Integrated Forecasting System aerosol module (IFS-AER) for the years 2016–2019 (cycles 41r1–46r1) are compared to vertical profiles of particle backscatter from the Deutscher Wetterdienst (DWD) ceilometer network. The system has been developed in the Copernicus Atmosphere Monitoring Service (CAMS) and its precursors. The focus of this article is to evaluate the realism of the vertical aerosol distribution from 0.4 to 8 km above ground, coded in the shape, bias and temporal variation of the profiles. The common physical quantity, the attenuated backscatter β∗(z), is directly measured and calculated from the model mass mixing ratios of the different particle types using the model's inherent aerosol microphysical properties. Pearson correlation coefficients of daily average simulated and observed vertical profiles between r=0.6–0.8 in summer and 0.7–0.95 in winter indicate that most of the vertical structure is captured. It is governed by larger β∗(z) in the mixing layer and comparably well captured with the successive model versions. The aerosol load tends to be biased high near the surface, underestimated in the mixing layer and realistic at small background values in the undisturbed free troposphere. A seasonal cycle of the bias below 1 km height indicates that aerosol sources and/or lifetimes are overestimated in summer and pollution episodes are not fully resolved in winter. Long-range transport of Saharan dust or fire smoke is captured and timely, only the dispersion to smaller scales is not resolved in detail. Over Germany, β∗(z) values from Saharan dust and sea salt are considerably overestimated. Differences between model and ceilometer profiles are investigated using observed in situ mass concentrations of organic matter (OM), black carbon, SO4, NO3, NH4 and proxies for mineral dust and sea salt near the surface. Accordingly, SO4 and OM sources as well as gas-to-particle partitioning of the NO3–NH4 system are too strong. The top of the mixing layer on average appears too smooth and several hundred meters too low in the model. Finally, a discussion is included of the considerable uncertainties in the observations as well as the conversion from modeled to observed physical quantities and from necessary adaptions of varying resolutions and definitions.
Highlights
Aerosol particles play a key role in atmospheric processes, and their manifold sources and transformations reflect in a wide range of abundance as well as chemical and physical properties
After brief overviews of the Copernicus Atmosphere Monitoring Service (CAMS) model and potential and limitations of the ceilometer data, we introduce the auxiliary data aiding the interpretation as well as the concept and metrics to categorize the results in Sect
A different perspective, transformed to the whole vertical profiles of monthly mean and median bias of β∗(z), is shown in Fig. 3 and color coded by each month for 2016 to 2019
Summary
Aerosol particles play a key role in atmospheric processes, and their manifold sources and transformations reflect in a wide range of abundance as well as chemical and physical properties. The understanding of particles’ net effects on air quality, weather, climate and chemical budgets still comprises significant uncertainties (Linares et al, 2009; WMO, 2013; Baklanov et al, 2014). Particles affect climate and weather directly by light scattering and absorption (Hansen et al, 1997; Ramanathan et al, 2007; WMO, 2013) and indirectly by altering the formation and droplet size of clouds (Lohmann et al, 2007) and via their impact on saturation and vertical exchange (Ackerman et al, 2000). Particle emissions and heterogeneous chemical processes degrade health-related air quality (Gilge et al, 2010; Karanasiou et al, 2012), but at the same time particles mediate gas-to-particle conversion, scavenging and final removal of trace gases from the atmosphere (Birmili et al, 2003; Kolb and et al, 2010)
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