Modelling of aerosol in the Greater Athens Area, Greece

Aerosols have recently been defined as a serious atmospheric pollution problem in the Greater Athens Area (GAA). This research is mainly focused on assessing the PM10 concentration levels in the GAA atmosphere through simulations. The model results of the chemical constituents of PM10 are satisfactory comparing to measurements; the discrepancies are attributed to the re-suspended and seaborne aerosols that are not simulated. Predictions and observations show a significant contribution of organic and sulphate species to the organic and inorganic fraction of PM10, respectively. After sensitivity tests were carried out, it is shown that the industrial activity results in higher PM10 concentrations and affects a greater area than transportation sources. Copyright © 2005 Inderscience Enterprises Ltd

An application of a simple Monte Carlo dispersion model in complex terrain

This paper discusses an attempt to investigate, air pollution transport problems by utilizing simple three-dimensional Monte Carlo schemes for instantaneous and continuous source releases in complex terrain. Observations of near-neutral balloon trajectories in Nisyros (Greece), a volcanic island in the Aegean Sea with highly complex terrain are used to gage the accuracy of mass-consistent flow algorithms for use in Monte Carlo schemes. Problems with the reproduction of the trajectories in such conditions are discussed. The mass-consistent algorithms which are frugal with respect to input data requirements and computational resources are shown to provide adequate fields for pollution advection computations. An example of such a concentration computation resulting from the operation of a proposed geothermal power plant is also presented. This paper discusses an attempt to investigate, air pollution transport problems by utilizing simple three-dimensional Monte Carlo schemes for instantaneous and continuous source releases in complex terrain. Observations of near-neutral balloon trajectories in Nisyros (Greece), a volcanic island in the Aegean Sea with highly complex terrain are used to gage the accuracy of mass-consistent flow algorithms for use in Monte Carlo schemes, Problems with the reproduction of the trajectories in such conditions are discussed. The mass-consistent algorithms which are frugal with respect to input data requirements and computational resources are shown to provide adequate fields for pollution advection computations. An example of such a concentration computation resulting from the operation of a proposed geothermal power plant is also presented

Modeling Extreme Warm-Air Advection in the Arctic: The Role of Microphysical Treatment of Cloud Droplet Concentration

As the Arctic climate is changing fast, with increasing areas of open water in summer, there is a growing interest in the processes related to the marginal ice zones. Recent studies have indicated that such a critical process may be the advection of warm and moist air from the south. In this study, the performance of the Weather Research and Forecasting (WRF) model is evaluated during an extreme warm advection episode over melting sea ice that occurred near the Arctic ice edge in summer 2014. The model gives a reasonably good representation of the atmospheric conditions and the Arctic boundary layer, characterized by very strong surface inversions and the frequent presence of low-level jets. However, the representation of the highly variable cloud conditions, from optically thick to optically thin, dissipating clouds, is sensitive to the choice of cloud droplet treatment in WRF. Simulations with relatively high cloud droplet number concentrations (Ndrop ≥ 100 cm−3) are more successful in representing the optically thick cloud state, whereas to reproduce optically thin and tenuous clouds Ndrop should be <50 cm−3. The WRF-Chem model, with a realistic treatment of the cloud-aerosol interactions, allows for large variations in Ndrop and hence can reproduce the cloud water properties reasonably well for most of the simulation time. This contributes to an improved representation of the cloud longwave radiative effect, compared to the simulations where a less adaptive treatment of Ndrop is applied. ©2019. American Geophysical Union. All Rights Reserved

Development and evaluation of an urban parameterization scheme in the Penn State/NCAR Mesoscale Model (MM5)

In the present study, the Penn State/NCAR Mesoscale Model (MM5) was modified by considering recent advances in the urban boundary layer. In particular, the modifications were carried out in two directions: (1) With respect to the thermal properties of an urban surface the surface energy balance was modified by taking into account the anthropogenic heat released in urban areas and the urban heat storage term to account for urban/building mass effects, including hysteresis; and (2) the surface stress and fluxes of heat and momentum were modified following recent advances in the atmospheric boundary layer over rough surfaces under unstable conditions. The whole process was supplemented by detailed information on land use cover, derived from satellite image analysis. The modifications were applied to the high-resolution nonlocal medium-range forecast planetary boundary layer parameterization scheme, based on work by Troen and Mahrt (1986). The improvements seen with the modified model, after comparison with available measurements of temperature and fluxes, refer to (1) the strengthening of the nocturnal urban heat island; (2) the changes in the temperature, which proved to be favorable through the whole diurnal cycle, resulting in decreasing the temperature amplitude wave; (3) the decrease of turbulence and fluxes during the daytime; and (4) the diffusion coefficient and potential temperature profiles that are reduced during daytime and are increased at the lower levels during the night and thus affect accordingly the mixing height. Copyright 2005 by the American Geophysical Union

Modeling Extreme Warm-Air Advection in the Arctic During Summer: The Effect of Mid-Latitude Pollution Inflow on Cloud Properties

Usually the Arctic is relatively free of anthropogenic influence in summer, which means that particles from natural sources can be the most significant nuclei for cloud droplets. However, this is not the case during anomalously warm-air intrusions when the air origin comes from lower latitudes. In this modeling study, we investigate the effect of mid-latitude pollution inflow (anthropogenic and biomass burning [BB]) on the aerosol-cloud-radiation interactions during an episode of extreme warm-air advection. This particular episode resulted in anomalously high air temperatures over the East Siberian Sea and has accelerated sea-ice melting. The impact of different emission sources on aerosol vertical distribution, chemical composition, cloud formation, and radiation budget is examined using the Weather Research and Forecasting model, fully coupled with chemistry. Elevated turbulent clouds that occurred at the beginning of the episode are found to be more sensitive to aerosol variations and their negative feedback on supersaturation, compared to stably stratified fog layers that were dominant during the core period. Omission of either anthropogenic or BB source results in decreased cloud liquid water and cloud droplet concentrations; however, these changes are not substantially large to significantly modify the net surface radiation budget. Significant reduction of the net surface radiation is only observed if both anthropogenic and BB transported pollution reaches the area of interest. © 2021. American Geophysical Union. All Rights Reserved

The role of planetary boundary-layer parameterizations in the air quality of an urban area with complex topography

The effect of different planetary boundary-layer (PBL) parameterization schemes on the spatial distribution of atmospheric pollution over the complex topography of the greater Athens area is investigated. Four PBL schemes originally implemented in a numerical meteorological model and a fifth one simulating the urban effect are examined. Two different atmospheric conditions are analyzed; a typical summer and a typical winter pollution episode. The relative importance of chemical and physical processes of the pollution predictions is discussed using process analysis. It is revealed that, for primary pollutants, a local scheme seems more adequate to represent the maximum observed concentrations while, completely different in structure, a non-local scheme reproduces the mean observed values in the basin. Concerning secondary pollutants, peak concentration differences, due to the different PBL schemes, are smoothed out. Nevertheless, the PBL scheme selection shapes the horizontal and the vertical extension of maximum values. The non-local and semi non-local schemes are superior to the others, favouring strong vertical mixing and transport towards the surface. The stronger turbulence accommodated effectively by the semi non-local urban scheme enhances ozone production along the sea-breeze axis and preserves the high ozone concentrations during the nighttime hours in the urban core. © Springer Science+Business Media B.V. 2009

Simulation of the effects of criticals factors on ozone formation and accumulation in the greater Athens area

In the present study, the temporal and spatial dynamics of the ozone production in the greater Athens area (GAA) is examined by using the photochemical UAM-V model coupled with the meteorological MM5 midel. Several numerical experiments were performed in order to investigate and to quantify the effect of critical factors that conduce to the ozone formation and accumulation during ozone episodes. The initial scenario is able to reproduce the observed ozone patterns, but it underestimates the observed peaks in most of the downwind suburban stations. Using process analysis, we demonstrate the contribution of chemical and physical processes to ozone formation and destruction. The inclusion of biogenic emissions and their distribution based on a satellite vegetation index, as well as the adjustment of the speciation of the anthropogenic NMVOC emissions according to specific characteristics measured in street and aged city plumes, lead to a more realistic description of the urban mixture and thus of the ozone production. The effect of the urban sector introduced via a simplified urbanized meteorological data set, provoke a differentiation of the spatial pattern attributed to the accumulation of the primary NOX pollutants inside the city center and to the consequent limited horizontal advection toward the peripheral zone. Finally, the ozone background turned out to be a key factor for the model performance. The statistical evaluation of the results reveals the importance and the necessity of implementing all the above modifications; the persistence of some discrepancies is associated with meteorological or modeling coupling limitations. Copyright 2007 by the American Geophysical Union

The effect of SRTM and Corine Land Cover data on calculated gas and PM10 concentrations in WRF-Chem

The goal of this study is to investigate the impact of the high resolution Shuttle Radar Topography Mission (SRTM) 90m×90m topography data, together with the 100m×100m resolution Corine Land Cover 2006 on the simulated gas and particulate matter (PM10) concentrations by WRF-Chem. We focused our analysis on the well-known highly urbanized region of the Po Valley. Large differences are found in the geographical distribution of the land cover classes between Corine Land Cover and 30 arc seconds USGS. The simulation with the SRTM and Corine Land Cover increases modelled temperature at 2m and reduces wind speeds due to more friction at the surface induced by the Corine Land Cover. Latent and sensible heat fluxes show large differences between the two simulations and the related boundary layer development and depth. The simulation with the SRTM and Corine Land Cover favours the precipitation amount over a large of part the Alps and follows the pattern of the difference in topography between the two topography data sets. In term of air quality indicators, impacts are also large and geographical dependent. Monthly average of CO, NO and SO2 concentrations over a large part of the Po Valley are higher when using Corine Land Cover, up to ~20, ~50 and ~55%, respectively. With respect to PM10, the impacts are also geographical dependent. Over the Po valley area, calculated PM10 concentrations are in general higher using Corine Land Cover (up to 6.7ug/m3 [~26%] westerly of Milan) while differences are smaller over the Alps (~0.25ug/m3 [~20%]). Although the scope of this work is not to evaluate the model performance in calculated meteorological parameters and gas and PM10 concentrations, calculated values by the simulation with SRTM and Corine Land Cover show a better agreement with the observations than the simulation with the USGS topography and land cover data sets. A quantitative comparison between modelled and observed monthly average PM10 concentrations shows that both simulations underestimate the observed PM10 concentrations by a factor ~4. The agreement is much better during episodes for the simulation with the SRTM and Corine Land Cover. For CO, SO2 and NOx, the modelled monthly mean concentrations are similar for the two simulations. Larger differences are found during some episodes and regions with the SRTM and Corine LC simulation being in better agreement with the observations. © 2014 Elsevier Ltd

Ozone production from the interaction of wildfire and biogenic emissions: A case study in Russia during spring 2006

The objective of this study is to investigate the contribution of biomass burning emissions to O3 production during small-scale dry-grass fires over Western Russia (24 April-10 May 2006) as well as to quantify the effect of biogenic emissions in this environment. By using the Factor Separation methodology, we evaluate the pure contribution of each one of these two sources and we appoint the significance of their synergistic effect on O3 production. The total (actual) contribution of each source is also estimated. Sensitivity simulations assess the effect of various fire emission parameters, such as chemical composition, emissions magnitude and injection height. The model results are compared with O3 and isoprene observations from 117 and 9 stations of the EMEP network, respectively. Model computations show that the fire episode determines the sensitivity of O3 chemistry in the area. The reference run which represents grass fires with high NO x/CO emission ratio (0.06) is characterized by VOC-sensitive O3 production. In that case, the pure impact of fire emissions on surface O3 is up to 40-45 ppb, while their synergistic effect with the biogenic emissions is proven significant (up to 8 ppb). Under a lower NO x/CO molar ratio (0.025, representative of agricultural residues), the area is characterized by NO x-sensitive chemistry and the maximum surface O3 predictions are almost doubled due to higher O3 production at the fire spots and lower fires' NO emissions. © 2012 Author(s)