PMSS and gral inter-comparison: Strengths and weaknesses of the two models in reproducing Urban NOx levels in a real case application

Air dispersion models are useful tools for quantifying pollutant concentrations in urban environment however many issues related to the dispersion estimation within urban canopy still persist. Most of them concern the emissions estimation, the flow field reconstruction between obstacles (buildings, bridges, tunnels, etc.) and the pollutant dispersion driven by the estimated flow field. This study presents results of a model inter-comparison conducted in a real case study, focusing on a 6 km x 6 km square domain covering the city of Modena (Italy), between two Lagrangian dispersion models set-up with the aim of estimating the NOx concentrations produced by traffic flow within the urban area of the city. Comparisons are made between the Graz Lagrangian Model (a.k.a. GRAL) and the Parallel Micro SWIFT and SPRAY (a.k.a. PMSS) modelling suite, in terms of dispersion concentrations and computing cost. The horizontal resolution for both the models is set to 4 meters and the traffic emissions estimation is based on a bottom-up approach: the PTV VISUM traffic model is used to estimate traffic flows on the Modena urban road network and the EMEP/EEA cold and hot emission factors are employed to estimate related emissions. All the other urban emission sources were considered to contribute to the regional background concentrations and estimated with the WRF-Chem model, which estimates also initial and boundary meteorological conditions (multi-scale approach). The general objective of the inter-comparison is to use equivalent input data for both the models keeping the emissions and the meteorological initial and boundary/condition consistent so that any discrepancies in output would be the results of differences in the micro-scale dispersion models. Since different turbulence parametrisation and dispersion scheme are implemented in the two models, the goal of this study is to identify the strengths and the weaknesses of both the models in reproducing urban NOx concentrations, in a real case application, at urban traffic and urban background sites

Optimisation of a one-step PCR assay for the diagnosis of Flavescence doreerelated phytoplasmas in field-grown grapevines and vector populations

Field-infected grapevines and natural populations of Scaphoideus titanus have been analysed to detect group V phytoplasmas associated with flavescence doree in northwestern Italy using nested PCR. A first amplification driven by universal ribosomal primers R16SF2/R2 was followed by a second round assisted by R16(V)F1/R1 primers and subsequent RFLP analysis. To optimize the test, nested PCRs were compared with direct amplification assisted by the group V-specific fAY/rEY primer pair, directed towards other ribosomal sequences. In nested and direct PCRs, respectively, DNAs from 71 and 57 out of 96 grapevines (i.e. 73.9 and 59.3 %) and 51 and 50 out of 108 insects (i.e. 47.2 and 46.3 %) reacted positively. Although it was not possible to determine the subgroup of the phytoplasmas after fAY/rEY amplification, these primers could be used successfully in mass screening of plant material and insect populations. They could detect, in single-step amplification, the phytoplasmas in 80 and 98 % of the plant and insect samples, respectively, that were already indexed as positive using nested PCR. This strongly reduced the number of samples requiring the nested approach, with beneficial effects on costs, labour and risks of the analysis.

A comparative study of mesoscale flow-field modelling in an Eastern Alpine region using WRF and GRAMM-SCI

Recently, the mesoscale model GRAMM-SCI has been further developed to make use of the freely available global ERA5 reanalysis dataset issued by the ECMWF. In this study, first results are discussed for the federal state of Styria, which is situated in the eastern Alps of Austria. Additional simulations were made with the mesoscale model WRF, which serve as a benchmark in this work. The model runs covered one week in summer and another one in winter dominated by fair weather conditions. These were characterized by the development of complex mountain wind systems in the Alps, which play an important role for the dispersion of pollutants. Regarding the bias and the root mean square error both models perform very well in comparison with existing studies for Alpine areas and are able to capture the main features of observed surface flows such as valley-wind systems or katabatic flows at slopes. In addition, observed calm wind conditions at many stations during the winter period were reproduced by the models. However, the correct simulation of wind directions in these conditions was found to be extremely challenging. Existing model quality criteria for wind direction seem to be too strict for low-wind-speed conditions. Therefore, based on theoretical and empirical considerations, a new model evaluation benchmark for wind direction is proposed, which takes into account the random nature of horizontally meandering flows in stagnant weather situations

Urban population exposure forecast system to predict NO2 impact by a building-resolving multi-scale model approach

Operational forecasting systems based on chemical transport models (CTMs) nowadays generally produce concentration maps with a resolution in the order of 2–5 km, very rarely exceeding the sub-kilometre scale. The main reason for this restriction is the prohibitive computing cost that a simulation covering an entire country would have if set-up with a resolution in the order of meters. In this paper a hybrid forecast system, relying on the WRF-Chem model coupled with the PMSS Lagrangian modelling suite, has been developed and applied for each day of February 2019, to predict hourly NO2 and NOx concentrations with a spatial resolution of 4 m, for the urban area of Modena (a city located in the central Po Valley). Simulated meteorological fields (temperature, wind speed and direction) were assessed at three urban stations, compliant with WMO standards, and modelled concentrations were compared with measurements at two urban air quality stations located at background and traffic sites. Results show that meteorological variables are well captured by the hybrid system and statistical performances are in line with the benchmark values suggested by the European Environmental Agency and with similar case studies focusing on the same area. Modelled NO2 and NOx concentrations, notwithstanding a slight underestimation mainly evident at urban traffic stations for NOx, present a large agreement with related observations. The NO2 Model Quality Objective, as defined by Fairmode guidelines, was met for both the urban stations and the other statistical indexes considered in the evaluation fulfilled the acceptance criteria for dispersion modelling in urban environment, for both NO2 and NOx concentrations. In the second section of the study, the population exposure to forecasted NO2 concentrations has been evaluated adopting a generic model of dynamic population activity. The population was distributed at hourly time steps in specific urban micro-environments at the same resolution of the concentration maps (4 m) and the short-term exposure has been computed as the product between the population density in each model cell and related surface NO2 concentrations. An infiltration factor was also applied to estimate indoor concentrations. The hybrid system was shown to be particularly suited for assessing short-term peak exposure in areas influenced by traffic emissions. On the other hand, due to the limited time spent by the population within traffic related environments, the long-term population exposure calculated by the hybrid system tends to be similar to the WRF-Chem stand-alone estimate