European Air Pollution Dispersion Model Research Articles

Comparison of four years of air pollution data with a mesoscale model

Air quality within the European Union (EU) is controlled by the Member States' monitoring networks. In this study, measured data is compared with the EURAD (EURopean Air pollution Dispersion) model system diagnostic output. Simulations for the German state North Rhine-Westphalia (NRW) with a horizontal grid resolution of 5km×5km are analyzed. The comparison is performed for NO2, O3, and PM10, for the 4-year time period from 2002 through 2005.Although the spatial representativity of data of the two systems differs, the analyzed temporal variability of the averages shows good agreement of modeled and observed concentrations for all three parameters. This confirms the applicability of the EURAD model to mesoscale air quality assessment. Discrepancies between the model and observed data occurred at low concentrations close to the detection limits of the analyzers, for high O3 concentrations in summer, and for PM10 before 2004, when earlier versions of the MM5 meteorological module and of the emission inventory were used.Possible causes of O3 overprediction and NO2 underprediction preferably showing up in summer are considered. It is found that modeled Ox=O3+NO2 leads to better representation of the observations than the individual species themselves. The model performance can probably be increased by further development of the emission inventories and more accurate land use data. These input data seem to be the main reason for deviations between observations and model results.

Dust storm simulation with regional air quality model – Problems and results

Abstract On 24 March 2007 an extraordinary dust plume was observed in the troposphere over Central Europe. Satellite observations revealed its origins in a dust storm in Southern Ukraine, where large amounts of soil were resuspended from dried-out farmlands by wind gusts up to 30 m/s. Maximum particulate matter (PM 10 ) mass concentrations between 200 and 1400 μg m −3 occurred in Slovakia, the Czech Republic, Poland, and Germany along the pathway of the plume from East to West. In order to achieve a better understanding of the processes involved and their interaction the numerical simulation of this event was done by using a new parameterization of dust emission under certain conditions. A simplified dust emission scheme, proposed by Shao (2004), is implemented in the EURAD –Model (European Air Pollution Dispersion Model). A possible way for simulation of other similar dust events in the future is described. The obtained results are compared with the available measurement data and are commented.

Ozone episode analysis by four‐dimensional variational chemistry data assimilation

A chemical four‐dimensional variational data assimilation system has been developed and applied for the study of an episode with enhanced summerly ozone levels. In this study the optimization parameters are the initial values of the chemical constituents. The case study focuses on an ozone episode over central Europe during August 1997. The associated observational database consists mainly of surface observations of ozone and nitrogen oxides, but also a limited number of ozone radiosonde records. The four‐dimensional data assimilation algorithm is composed of the chemistry transport model, its adjoint model with the adjoint versions of the Regional Acid Deposition Model (RADM2) chemical mechanism, horizontal and vertical advection schemes, implicit vertical diffusion, and a limited memory quasi‐newton minimization routine. The underlying model of the spatio‐temporal data assimilation scheme is the comprehensive mesoscale‐α EUropean Air pollution Dispersion model (EURAD), which is based on the RADM2 gas phase mechanism. On the basis of a 6 hours data assimilation interval, analyses of the chemical state of the atmosphere were obtained, where the skill is verified in two different ways: (1) improvements of forecasts subsequent to the assimilation procedure, and (2) validation of the analyses with observational data which is withheld from the variational data assimilation algorithm. It is demonstrated that significant improvements are achieved for short‐term forecasts including the afternoon ozone peak abundances. The analysis skill is further corroborated by examinations with retained measurement data.

Estimation of Cross-Tropopause Airmass Fluxes at Midlatitudes: Comparison of Different Numerical Methods and Meteorological Situations

Airmass flux across the tropopause modifies the budget of chemically reactive minor constituents in the stratosphere and the troposphere. Flux estimates reported in the literature exhibit large discrepancies, mainly due to the application of different estimation algorithms and examination of different episodes. The different studies also focus on different exchange mechanisms. With the aim of contributing to clarification of the situation, two different methods of cross-tropopause mass transfer calculations are implemented into the mesoscale- a European Air Pollution Dispersion model system and discussed: a trajectory-based analysis and the method developed by Wei. These methods are applied to an episode in February 1997, when a deep stratospheric intrusion occurred over the North Atlantic and western Europe. Comparison of the results shows good agreement between the net flux values computed by the different methods, both yielding values near 1 3 1023 kg m22 s21 for the net airmass flux from the stratosphere to the troposphere. Analyzing the tendency of potential vorticity along trajectories, it is shown that in this case turbulent processes surpass the diabatic ones and are mainly responsible for the transformation from stratospheric into tropospheric air. Employing the method of trajectory analysis, different meteorological situations are investigated in order to establish a broader range of cross-tropopause transport estimates for middle latitudes. For all analyzed cases a net downward transport from stratosphere to troposphere was found. The results vary between 0.6 and 1.0 3 1023 kg m22 s21 for the airmass flux across the two potential vorticity unit surface, taken as the dynamical tropopause.

4D-variational data assimilation with an adjoint air quality model for emission analysis

The problem of analyzing the chemical state of the troposphere and the associated emission scenario on the basis of observations and model simulations is considered. The method applied is the four-dimensional variational data assimilation method (4D-var) which iteratively minimizes the misfit between modeled concentration levels and measurements. The overall model–observation discrepancy is measured in terms of a cost function, of which the gradient is calculated for subsequent minimization by adjoint modeling. The model applied is the University of Cologne EURopean Air pollution Dispersion model (EURAD) simulating the meso-alpha scale. The forward and adjoint components are Bott's horizontal and vertical advection scheme (Bott, Mon. Wea. Rev. 117 (1989), 1006), implicit vertical diffusion, and the RADM2 gas phase chemistry. The basic feasibility of the adjoint modeling technique for emission rate assessment is demonstrated by identical twin experiments. The objective of the paper is to demonstrate the skill and limits of the 4D-var technique to analyze the emission rates of non-observed precursor constituents of ozone, when only ozone observations are available. It is shown that the space–time variational approach is able to analyze emission rates of NO directly. For volatile organic compounds (VOC), regularization techniques must be introduced, however.

Modal aerosol dynamics model for Europe: development and first applications

The Modal Aerosol Dynamics model for Europe (MADE) has been developed as an extension to mesoscale chemistry transport models to allow a more detailed treatment of aerosol effects in these models. Due to the complexity of the atmospheric aerosol system an approach has been chosen which is, on the one hand, fast enough for this application and, on the other, provides sufficient information on the particle size distribution. In MADE, which is developed from the regional particulate model (RPM) the particle size distribution of the submicrometer aerosol is represented by two overlapping lognormal modes. The chemical composition is currently treated in the sulfate–nitrate–ammonium and water system. Sources for aerosol particles are modelled through nucleation and emission. Coagulation, condensation, transport and deposition are considered as processes modifying the aerosol population in the atmosphere. Aerosol dynamics calculations are performed on-line within the chemistry-transport model. Process studies with a one-dimensional version of the model system are used to investigate the relative importance of the individual aerosol dynamic processes and the important links between between the gas and aerosol phase as well as meteorological parameters. Results from a first three-dimensional application of the fully coupled system of MADE and the European Air Pollution Dispersion model system (EURAD) are presented, showing the suitability of MADE as an aerosol dynamics model even within complex air quality models. The application of the new aerosol model provides information on particle number, size and surface area in addition to the chemical concentration fields, which can be used to study a variety of aerosol-related air pollution issues in subsequent studies.

Variational data assimilation for tropospheric chemistry modeling

The method of variational adjoint data assimilation has been applied to assimilate chemistry observations into a comprehensive tropospheric gas phase model. The rationale of this method is to find the correct initial values for a subsequent atmospheric chemistry model run when observations scattered in time are available. The variational adjoint technique is esteemed to be a promising tool for future advanced meteorological forecasting. The stimulating experience gained with the application of four‐dimensional variational data assimilation in this research area has motivated the attempt to apply the technique to air quality modeling and analysis of the chemical state of the atmosphere. The present study describes the development and application of the adjoint of the second‐generation regional acid deposition model gas phase mechanism, which is used in the European air pollution dispersion model system. Performance results of the assimilation scheme using both model‐generated data and real observations are presented for tropospheric conditions. In the former case it is demonstrated that time series of only few or even one measured key species convey sufficient information to improve considerably the analysis of unobserved species which are directly coupled with the observed species. In the latter case a Lagrangian approach is adopted where trajectory calculations between two comprehensively furnished measurement sites are carried out. The method allows us to analyze initial data for air pollution modeling even when only sparse observations are available. Besides remarkable improvements of the model performance by properly analyzed initial concentrations, it is shown that the adjoint algorithm offers the feasibility to estimate the sensitivity of ozone concentrations relative to its precursors.