Search

This review paper provides a framework for the application of the Observing System Simulation Experiment (OSSE) methodology to satellite observations of atmospheric constituents relevant for air quality. The OSSEs are experiments used to determine the potential benefit of future observing systems using an existing monitoring or forecasting system and by this can help to define optimal characteristics of future instruments. To this end observations from future instruments are simulated from a model representing the realistic state of the atmosphere and an instrument simulator. The added value of the new observations is evaluated through assimilation into another model or model version and comparison with the simulated true state and a control run. This paper provides an overview of existing air quality OSSEs focusing on ozone, CO and aerosol. Using illustrative examples from these studies we present the main elements of an air quality OSSE and associated requirements based on evaluation of the existing studies and experience within the meteorological community. The air quality OSSEs performed hitherto provide evidence of their usefulness for evaluation of future observations although most studies published do not meet all the identified requirements. Especially the evaluation of the OSSE set-up requires more attention; the differences between the assimilation model and the simulated truth should approximate differences between models and real observations. Although this evaluation is missing in many studies, it is required to ensure realistic results. Properly executed air quality OSSEs are a valuable and cost effective tool to space agencies and instrument builders when applied at the start of the development stage to ensure future observations provide added value to users of Earth Observation data. [ABSTRACT FROM AUTHOR]

Abstract: There is often a large discrepancy between the questions raised by policy makers and the responses offered by scientists. Current modeling approaches do not answer some of the typical questions that decision-makers face, as they do not provide solutions to policy-makers dealing with concrete political negotiation and decisions. In this paper, we try to bridge the gap by creating an integrated model chain that can respond to such concrete policy questions. The paper describes a model chain consisting of an activity-based transport model, a road traffic emission model, a bi-gaussian atmospheric dispersion model and a concentration measurement interpolation model. Subsequently results are compared to observations, in order to test its usability for simulating air quality and assessing dynamic exposure. The model is shown to represent the main cycles governing air quality, such as the intra-daily, the intra-weekly and the intra-annual cycle. Finally, this paper provides an example of the use of such a model chain by assessing the impact of different trip motives on the intra-daily NO2 cycle. [Copyright &y& Elsevier]

Abstract: Chemical plants, refineries, transportation of hazardous materials are some of the most attractive facilities for external attacks aimed at the release of toxic substances. Dispersion of these substances into the atmosphere forms a concentration distribution of airborne pollutants with severe consequences for exposed individuals. For emergency preparedness and management, the availability of assessed/validated dispersion models, which can be able to predict concentration distribution and thus dangerous zones for exposed individuals, is of primary importance. Air quality models, integral models and analytical models predict the transport and the turbulent dispersion of gases or aerosols after their release without taking into account in detail the presence of obstacles. Obstacles can modify the velocity field and in turn the concentration field. The Computational Fluid Dynamics (CFD) models on the other hand are able to describe such phenomena, but they need to be correctly set up, tested and validated in order to obtain reliable results. Within the project Europa-ERG1 TA 113.034 "NBC Modelling and Simulation" several different approaches in CFD modelling of turbulent dispersion in closed, semi-confined and urban-like environment were adopted and compared with experimental data and with operational models. In this paper the results of a comparison between models describing the dispersion of a neutral gas in an idealized urban-like environment are presented and discussed. Experimental data available in the literature have been used as a benchmark for assessing statistical performance for each model. Selected experimental trials include some water channel tests, that were performed by Coanda at 1:205 scale, and one full-scale case that was tested in the fall of 2001 at the Dugway Proving Grounds in Utah, using an array of shipping containers. The paper also suggests the adoption of improved statistical parameters in order to better address differences between models, and to have a more straightforward method for comparing models suitable for emergency preparedness aims. [Copyright &y& Elsevier]

Abstract: This paper presents a multi-pollutant sensitivity study of an air quality model over Europe with a focus on aerosols. Following the evaluation presented in the companion paper, the aim here is to study the sensitivity of the model to input data, mathematical parameterizations and numerical approximations. To that end, 30 configurations are derived from a reference configuration of the model by changing one input data set, one parameterization or one numerical approximation at a time. Each of these configurations is compared to the same reference simulation over two time periods of the year 2001, one in summer and one in winter. The sensitivity of the model to the different configurations is evaluated through a statistical comparison between the simulation results and through comparisons to available measurements. The species studied are ozone (O3), nitrogen dioxide (NO2), sulfur dioxide (SO2), ammonia (NH3), coarse and fine aerosol particles (PM c and PM2.5), sulfate, nitrate, ammonium, chloride and sodium. For all species, the modeled concentrations are very sensitive to the parameterization used for vertical turbulent diffusion and to the number of vertical levels. For the other configurations considered in this work, the sensitivity of the modeled concentration to configuration choice varies with the species and the period of the year. O3 is impacted by options related to boundary conditions. PM c is sensitive to sea-salt related options, to options influencing deposition and to options related to mass transfer between gas and particulate phases. PM2.5 is sensitive to a larger number of options than PM c : sea-salt, boundary conditions, heterogeneous reactions, aqueous chemistry and gas/particle mass transfer. NO2 is strongly influenced by heterogeneous reactions. Nitrate shows the highest variability of all species studied. As with NO2, nitrate is strongly sensitive to heterogeneous reactions but also to mass transfer, thermodynamic related options, aqueous chemistry and computation of the wet particle diameter. While SO2 is mostly sensitive to aqueous chemistry, sulfate is also sensitive to boundary conditions and, to a lesser extent, to heterogeneous reactions. As with nitrate, ammonium is largely impacted by the different configuration choices, although the sensitivity is slightly lower than for nitrate. NH3 is sensitive to aqueous chemistry, mass transfer and heterogeneous reactions. Chloride and sodium are impacted by sea-salt related options, by options influencing deposition and by options concerning the aqueous-phase module. [Copyright &y& Elsevier]

Abstract: Urban Heat Island (UHI) has significant impacts on the buildings energy consumption and outdoor air quality (OAQ). Various approaches, including observation and simulation techniques, have been proposed to understand the causes of UHI formation and to find the corresponding mitigation strategies. However, the causes of UHI are not the same in different climates or city features. Thus, general conclusion cannot be made based on limited monitoring data. With recent progress in computational tools, simulation methods have been used to study UHI. These approaches, however, are also not able to cover all the phenomena that simultaneously contribute to the formation of UHI. The shortcomings are mostly attributed to the weakness of the theories and computational cost. This paper presents a review of the techniques used to study UHI. The abilities and limitations of each approach for the investigation of UHI mitigation and prediction are discussed. Treatment of important parameters including latent, sensible, storage, and anthropogenic heat in addition to treatment of radiation, effect of trees and pond, and boundary condition to simulate UHI is also presented. Finally, this paper discusses the application of integration approach as a future opportunity. [Copyright &y& Elsevier]

Abstract: This paper is devoted to the study of pollutant concentration distribution within urban-like geometries. By applying efficiency concepts originally developed for indoor environments, the term ventilation is used as a measure of city “breathability”. It can be applied to analyse pollutant removal within a city in operational contexts. This implies the evaluation of the bulk flow balance over the city and of the mean age of air. The influence of building packing density on flow and pollutant removal is, therefore, evaluated using those quantities. Idealized cities of regular cubical buildings were created with packing density ranging from 6.25% to 69% to represent configurations from urban sprawl to compact cities. The relative simplicity of these arrangements allowed us to apply the Computational Fluid Dynamics (CFD) flow and dispersion simulations using the standard k–ɛ turbulence model. Results show that city breathability within the urban canopy layer is strongly dependent from the building packing density. At the lower packing densities, the city responds to the wind as an agglomeration of obstacles, at larger densities (from about 44%) the city itself responds as a single obstacle. With the exception of the lowest packing density, airflow enters the array through lateral sides and leaves throughout the street top and flow out downstream. The air entering through lateral sides increases with increasing packing density. At the street top of the windward side of compact building configurations, a large upward flow is observed. This vertical transport reduces over short distance to turn into a downward flow further downstream of the building array. These findings suggest a practical way of identifying city breathability. Even though the application of these results to real scenarios require further analyses the paper illustrates a practical framework to be adopted in the assessment of the optimum neighbourhood building layout to minimize pollution levels. [Copyright &y& Elsevier]

A fine-resolution, meso-urban meteorological model was updated and applied, using new data and techniques in this study, in driving fine-resolution photochemical simulations to evaluate the air-quality impacts of urban heat island mitigation. The drag-force-based formulation of the model improves the simulation of fine-resolution meteorological and air-pollutant concentration fields in the urban canopy layer. Compared to the meso scale, the meso-urban modeling of heat island mitigation produces larger localized impacts on meteorology and ozone air quality and captures phenomena of interest that are typically not detectable at the coarser scale. These include, for example, cool islands, heat islands, flow convergence associated with heat island circulation, flow divergence at the leading edge of urban areas, and vertical variation in turbulent kinetic energy budget components within the canopy layer in response to vertical changes in densities of buildings and vegetation. They also include fine-resolution features in the simulated ozone concentration field and its response to surface modifications. Model results show that heat island mitigation is effective in reducing local ozone concentrations. This paper presents results from Sacramento, California, as an example using increased urban albedo as the control mechanism. For the region, episodic conditions, and surface modification scenarios examined in this paper, air temperature is decreased by up to 3°C. Changes in ozone consist overwhelmingly of decreases but can also involve increases with the latter being confined to small areas and short time intervals. While larger reductions in ozone are detected, decreases of up to 5–10ppb are more representative and the daily maximum 8-h average can be decreased by up to 13%. [Copyright &y& Elsevier]

Abstract: This paper presents results from a study led prior to the launch of the EPS-MetOp satellite in October 2006. It aims at assessing the feasibility of assimilating MetOp troposphere ozone soundings within a regional chemistry-transport model, in view of improving air quality forecast in the lowest layers of the troposphere. The paper furthermore analyses the computational complexity of assimilating satellite data, and concludes on the necessity of providing grid support to satellite data assimilation. [Copyright &y& Elsevier]

In the companion paper, we showed that MM5 simulation using a satellite-derived high resolution Texas Forest Service (TFS) land use and land cover (LULC) data set (M2), compared to the MM5 results with the default USGS-LULC (M1), improved representation of the complicated features of the atmospheric planetary boundary layer (PBL) in the Houston ship channel (HSC) area, where large industrial emission sources are concentrated. In the present paper, the study is extended to investigate these effects on air quality simulations. Two emission inputs, namely E1 and E2, are prepared with the M1 and M2 meteorology data, respectively, to reflect the differences in the point source plume rise estimates while keeping the biogenic and mobile emissions the same. Air quality simulations were performed with CMAQ using the M1E1 and M2E2 inputs. The simulation results demonstrate the importance of utilizing high resolution LULC data. In the default LULC data, the HSC area was classified as grass land cover, and MM5 predicted confined mixing, resulting in over-prediction of ozone (O3) precursors, such as NO x (NO plus NO2), and highly reactive volatile organic compounds (HRVOC) species, including ethylene and propylene, over the HSC area. In the TFS data, the area was classified as the impervious “urban” land use and MM5 predicted enhanced mixing of the precursor species, leading to better agreements with measurements. The high resolution LULC also resolves the location of water body near the HSC more accurately, predicting shallower PBL heights than the default LULC during daytime. With favorable wind conditions, the O3 precursors were transported from the HSC emission source towards the area, trapping the pollutants in a confined shallow mixing layer that occasionally led to a rapid photochemical production of O3. The above comparison includes the changes in both meteorological and plume-rise emissions inputs. We performed two additional CMAQ simulations using the same meteorological result (M2) but with different emission point sources E1 and E2 to determine the importance of emission changes on the air quality simulations. The sensitivity tests with the different plume-rise emission inputs due to two different meteorological inputs show little impact on the air quality simulations in this case. [Copyright &y& Elsevier]

This paper reports on the development and evaluation of a new modelling system for studying air quality on local scales. A multi-model approach has been adopted to develop the OSCAR Air Quality Modelling System to conduct assessments at different levels of complexity. This work focuses on the evaluation of the performance of two of the models, CAR II (semi-empirical, annual averaged model) and CAR-FMI (line-source Gaussian model for hourly predictions), as integrated into the OSCAR System and employing consistent emissions and meteorological inputs. The models have been evaluated using measured NOx, NO2, PM10 and PM2.5 data for 2003 from the Vallila (Helsinki) and Cromwell Road (London) monitoring stations; both of these stations are located in urban roadside environments. The evaluation consists of comparisons of annual averaged and hourly predicted and measured data, as well as detailed statistical analysis of the model performance. Overall, closer agreement between the modelled and measured data is observed for the Vallila site, where traffic levels are medium, but the models show significant underestimation for Cromwell Road which is subject to high traffic levels. The paper also discusses possible reasons for this underestimation. The wider implications of the work are also stated for development and evaluation of environmental models. [Copyright &y& Elsevier]

Uncontrolled natural ventilation systems tend, by their nature, to deliver varying flow rates that are not necessarily optimised for human comfort or energy efficiency. Moreover these ventilation flow rates may not be delivered along the intended flow paths through a building, possibly further reducing ventilation effectiveness and increasing ventilation heat losses. These characteristics make natural ventilation systems a suitable candidate for ventilation demand control where the levels of fresh air delivered respond to a sensed parameter that indicates the level of ventilation demand. This paper makes a preliminary, comparative assessment of the impact an active supply-side CO 2 ventilation demand control system may have on the ventilation regime, flow levels and space heating consumption of a two-storey naturally ventilated domestic property. The dwelling is modelled in EnergyPlus and the performance of the ventilation demand control system simulated using EnergyPlus’ run-time Energy Management System. Simulations are conducted for a variety of temperate climate contexts and building fabric leakage levels. The simulations demonstrate that the ventilation demand control system could reinforce desired flow regimes and provide comparable indoor air quality compared to the uncontrolled base case whilst delivering significant reductions in space heating consumption. [ABSTRACT FROM AUTHOR]

Air quality problems are attracting much attention in Hong Kong (HK) and the Pearl River Delta (PRD) in China. The complex and regional characteristics of air quality problems call for a comprehensive modelling system with a highly reliable simulation and effective communication tools for decision-makers and participants from multiple disciplines. In this paper, we used a modelling management method to develop a Cyberinfrastructure system that couples meteorological and air quality models with a visual analysis to improve the cognition and management of air quality problems. The database management of both the data and the modelling parameters is an innovative advantage of this system; this will be helpful not only for sharing modelling knowledge but also for improving the acknowledgement of modelling scenarios, which are usually conducted by various stakeholders. On the basis of 19 categories of emission inventories that provide detailed information about multiple pollutants in the 11 cities in the study area, this system provides an authoritative and adjustable emission inventory to draw an accurate scientific picture for decision-makers. We applied this system to a case study to investigate the effects of emission control of nitrogen dioxide from vehicles in HK and the PRD on air quality. The simulation showed that the air quality improvement from emission control was very limited and suggested that regional and super-regional co-operation involving the comprehensive emission control of multiple pollutants may be more effective in creating a better future. [ABSTRACT FROM AUTHOR]

Traffic is one of the main sources of particulate matter (PM) inside urban areas. This paper provides a preliminary assessment of the potential to reduce outdoor PM concentrations by local removal inside semi-enclosed parking garages. The assessment is performed by computational fluid dynamics (CFD) based on the 3D steady RANS equations and an Eulerian advection-diffusion equation. First, an extensive CFD validation study is performed with gas dispersion wind-tunnel measurements. Next, the case study for Eindhoven city center is conducted on a high-resolution grid including 16 semi-enclosed garages. Traffic intensities on the streets and in the garages are converted to PM 10 source terms. The garages are ventilated with outdoor air. Simulations are performed with and without removal units in the garages. The case study is not intended to reproduce a particular pollution episode but to provide a preliminary indication of the potential reduction in PM 10 for representative meteorological and traffic conditions. The results show that 594 removal units allow reductions in local outdoor PM 10 by up to 50% close to the garages while reductions up to 10% are achieved further downstream. It is concluded that local removal in semi-enclosed parking garages can be an effective strategy towards improved outdoor air quality. [ABSTRACT FROM AUTHOR]

Assessment of air pollutant profiles by using measurements involves some limitations in the implementation. For this, deterministic air quality models are often used. However, its simulation usually needs high computational requirements due to complex chemical reactions involved. In this paper, a neural network-based metamodel approach is used in conjunction with a deterministic model and some measured data to approximate the non-linear ozone concentration relationship. For this, algorithms for performance enhancement of a radial basis function neural network (RBFNN) are developed. The proposed method is then applied to estimate the spatial distribution of ozone concentrations in the Sydney basin. The experimental comparison between the proposed RBFNN algorithm and the conventional RBFNN algorithm demonstrates the effectiveness and efficiency in estimating the spatial distribution of ozone level. [ABSTRACT FROM AUTHOR]

This paper introduces a method for a full assessment of the internal air movement characteristics in a room ventilated with a commercial wind tower using scaled wind tunnel and computational fluid dynamics (CFD) analysis. An accurate geometrical representation of the experimental situation was recreated in the CFD simulation. The experimental investigation was carried out using a closed-loop low speed wind tunnel and the indoor air flow distribution was measured and compared with the CFD analysis. Good correlation between the numerical and experimental results was observed (10% average error). Flow visualisation was also conducted to further analyse the airflow structure within the room. The work assessed several ventilation parameters to describe the indoor airflow characteristics such as the mean age of air (MAA), air change rate, and air change effectiveness (ACE). The MAA was calculated using the steady-state method, by solving an additional partial differential equation describing the transport of the scalar “age of air”. The numerical analysis of the MAA allowed to detect less or insufficiently ventilated areas. The CFD code could be useful for the calculation of the MAA and ACE, allowing reduction in time and cost in the evaluation of indoor air quality in buildings ventilated with wind tower or similar device. [ABSTRACT FROM AUTHOR]

The development of surrogate safety measures is essential due to the problems of availability and quality of historical crash data. The Aggregate Conflict Propensity Metric (ACPM) is a surrogate metric recently proposed and it is based on conflict studies and traffic simulations. ACPM is expected to be capable of assessing the relative safety levels of traffic facilities and/or treatments in order to help traffic engineers to select appropriate treatments based on traffic safety estimates. This paper presents three experimental tests conducted to evaluate the reliability of ACPM. In each test, ACPM is compared to a traditional conflict indicator in terms of identifying and ranking safety of traffic conditions under various traffic volumes based on traffic simulations. ACPM shows its strength and reliability in all three tests, as it provides results highly consistent with the Highway Safety Manual. The experimental tests indicate that ACPM is a promising surrogate safety measure that can appropriately identify relative safety among traffic treatments and/or facilities and provide traffic engineers with useful information on potential safety impact. [ABSTRACT FROM AUTHOR]

Urban form controls the overall aerodynamic roughness of a city, and hence plays a significant role in how air flow interacts with the urban landscape. This paper reports improved model performance resulting from the introduction of variable surface roughness in the operational air-quality model ADMS-Urban (v3.1). We then assess to what extent pollutant concentrations can be reduced solely through local reductions in roughness. The model results suggest that reducing surface roughness in a city centre can increase ground-level pollutant concentrations, both locally in the area of reduced roughness and downwind of that area. The unexpected simulation of increased ground-level pollutant concentrations implies that this type of modelling should be used with caution for urban planning and design studies looking at ventilation of pollution. We expect the results from this study to be relevant for all atmospheric dispersion models with urban-surface parameterisations based on roughness. [Copyright &y& Elsevier]

Abstract: High resolution model estimates (10×10km2) of tropospheric NO2 column amounts from the Comprehensive Air Quality Model (CAMx) for the Balkan Peninsula are compared with OMI/Aura measurements (13×24km2 at nadir) for the year April 2009 to March 2010. The Balkan area contributes significantly to the NO2 burden in European air and so numerous urban, industrial and rural regions are studied aiming to investigate the consistency of both satellite retrievals and model predictions at high spatial resolution. It has already been shown that OMI can detect the tropospheric column of NO2 over polluted Balkan cities due to its fine horizontal resolution and instrument sensitivity (Zyrichidou et al., 2009). In this study the improved OMI DOMINO v2.0 satellite retrievals showed that over South-Eastern Europe the monthly mean NO2 tropospheric column density fluctuated between 2.0 and 5.7±1.1×1015 molecules/cm2 over urban areas, 1.6–5.0±0.7×1015 molecules/cm2 over large industrial complexes and 1.1–2.2±0.4×1015 molecules/cm2 over rural areas for the year studied. The Comprehensive Air Quality Model with extensions (CAMx) version 4.40 is a publicly available open-source computer modeling system for the integrated assessment of gaseous and particulate air pollution. The anthropogenic emissions used in CAMx for the Greek domain being studied were compiled employing bottom-up approaches (road transport sector, off-road machinery, etc.) as well as other national registries and international databases. The rest of the Balkan domain has natural and anthropogenic emissions based on the TNO emission inventory of 2003. The high-resolution CAMx simulations reveal consistent spatial and temporal patterns with the OMI/Aura data. The annual spatial correlation coefficient between OMI and CAMx computed in this high spatial resolution analysis is of the order of 0.6, somewhat improved over those estimated in Zyrichidou et al. (2009) (R ≈0.5). However, in such a validation study it is important to take into account the averaging kernel (AK) information in order to achieve the creation of comparable data sets. Minor differences are found for area-averaged model columns with and without applying the kernel, which shows that the impact of limiting the effect of the a priori profile on the comparison is on average small. The main aim of the paper, which was to evaluate OMI retrieved and high resolution simulated tropospheric NO2 column densities over South-Eastern Europe and to assess the use of the averaging kernels, is achieved and the two data sources are being employed further in an inverse emission inventory creation study (Zyrichidou et al., in preparation). [Copyright &y& Elsevier]

Abstract: An improved air distribution system for aircraft cabin was proposed in this paper. Personalized outlets were introduced and placed at the bottom of the baggage hold. Its ratio of fresh air to recirculation air and the conditioned temperature of different types of inlets were also designed carefully to meet the goals of high air quality, thermal comfort and energy saving. Some experiments were conducted to evaluate and compare its performances with two other systems. First the Flow Visualization with Green Laser (FVGL) technology was used to analyze the air flow. The top-in-side bottom-out pattern may have the disadvantages of an indirect path to deliver fresh air to passengers, a low fresh air utilization ratio and the potential to widely spreading airborne infectious diseases. The bottom-in-top-out pattern can overcome these disadvantages very well, but it also faces the stratification of contaminated air above the head of the passengers. The improved pattern may overcome the above challenges quite well while also delivering good ventilation performance. The modified Personal Exposure Effectiveness (PEE) was measured to compare their performances with regard to inhaled air quality. The measured results suggest that personalized inlet should be designed to adjust its supply air angle according to the height of the passenger''s face to provide a higher fresh air utilization effectiveness and better air quality for passengers in the improved pattern. Some simulations revealed that the improved pattern had the potential to save energy by decreasing the amount of fresh air without significantly affecting air quality and thermal comfort. [Copyright &y& Elsevier]

Abstract: This paper discusses some of the differences between online and offline approaches for both air quality forecasting and numerical weather prediction, and argues in favor of an eventual migration to integrated modeling systems that allow two-way interactions of physical and chemical processes. Recent studies are used that directly compared online and offline simulations to discuss possible shortcomings for both air quality and weather forecasting. The disadvantages of offline approaches are easy to show for air quality forecasting. On the other hand, a positive impact on short to medium range weather forecasts that is significant enough to justify an implementation at operational weather forecasting centers is more difficult to prove, and may initially only come through an improvement of the meteorological data assimilation. Eventually though, a migration to an integrated modeling system will provide new opportunities for weather prediction modelers as well. The simulation of chemical species will allow identification of shortcomings in currently used forecast models as well as lead to better use of meteorological data assimilation. [Copyright &y& Elsevier]

Abstract: Although conventional CO2-based demand-controlled ventilation strategies, such as proportional and exponential controls, can ensure buildings/spaces meeting the minimum requirements of outdoor air by industry standards, they are operated under the assumption of equilibrium condition which can hardly be reached in practice and therefore there is still much space to improve on conventional strategies in terms of energy saving. In this paper, a novel and dynamic control strategy was developed for hourly scheduled buildings. The strategy utilized schedules by setting a base ventilation rate for unoccupied periods and calculating ventilation rate dynamically at each occupied period by solving the CO2 mass balance equation to keep indoor CO2 near the set point during the occupied period. Experimental simulations were made over a sports training center using both simulated and experimental CO2 generation rates. Results show that the new strategy can save +34% of energy related to ventilation air compared to proportional control. The new strategy was also extended to common buildings which are occupied for almost all opening hours. In the case of common buildings, the new strategy can save about +26% of energy related to ventilation air compared to proportional control. The new strategy is simple, dynamic, flexible and efficient. [Copyright &y& Elsevier]

Abstract: In this paper, we examine the extent to which an ensemble generated from a single air quality model correctly represents the global uncertainty of ozone simulations with a regional scale chemistry-transport model and whether it is suitable for ozone data assimilation. An ensemble of 30 members is constructed from a reference simulation in which the model parameters that are the most uncertain for determining ozone concentrations are randomly perturbed. Comparisons of the simulated ensemble using the model CHIMERE with observations are examined over the summer season both at the surface and higher in the troposphere. Although the ensemble overestimates vertical and horizontal correlation between errors, the average model error is well represented both at the surface and in the vertical dimension (after an adjustment for the latter). A variability of about 7–8ppb is found. The results found in this study with respect to tropospheric ozone model errors and error correlation lengths both from ensemble simulations and model to observation comparisons are of particular interest for data assimilation when constructing model error covariance matrices. [ABSTRACT FROM AUTHOR]

Abstract: Recent research has highlighted the substantial health-related costs of air pollution in the Hong Kong Special Administrative Region (HKSAR) and the potential threat from air pollution to HKSARs economic competitiveness. In order to address the air pollution problems, this paper seeks to analyse the individual contributions of major sulphur dioxide (SO2) sources in the Pearl River Delta Region (PRDR) (Pearl River Delta + HKSAR) on the air quality in the HKSAR. This study employed the coupling of the MM5/CALMET system with the CALPUFF, the multi-layer, non-steady-state puff dispersion model, where major power plants, marine vessels and vehicles, all in the PRDR, are taken into account. The observation data and simulation results at 11 Hong Kong Environmental Protection Department (HKEPD) general (non-road-side) stations are analyzed. Urban (in-zone) and Rural (out-zone) stations are defined in order to examine the SO2 contribution of different emission sources in different regions of the HKSAR. The model results show that the contribution of the HKSAR marine sources is significant both in summer and in winter, especially for the locations around the in-zone stations (in general 60%, and 55% in summer and winter respectively). In addition, the contribution of the HKSAR power plants is slightly higher than that of the PRD power plants in early summer, with a contribution difference of up to 20% when the prevailing wind is from the south. However, in late summer, this situation reverses. In winter, the contribution of the PRD power plants is two to three times greater than that of the HKSAR power plants. Moreover, Yantian port affects the northern part of the HKSAR when a northeasterly wind dominates the HKSAR. In order to solve these air pollution problems, the main implication of these results suggests that the HKSAR government, in close co-operation with the Guangdong government, needs to take immediate action. [ABSTRACT FROM AUTHOR]

Abstract: This paper compares spatial and seasonal variations and temporal trends in modeled and measured concentrations of sulfur and nitrogen compounds in wet and dry deposition over an 18-year period (1988–2005) over a portion of the northeastern United States. Substantial emissions reduction programs occurred over this time period, including Title IV of the Clean Air Act Amendments of 1990 which primarily resulted in large decreases in sulfur dioxide (SO2) emissions by 1995, and nitrogen oxide (NOx) trading programs which resulted in large decreases in warm season NOx emissions by 2004. Additionally, NOx emissions from mobile sources declined more gradually over this period. The results presented here illustrate the use of both operational and dynamic model evaluation and suggest that the modeling system largely captures the seasonal and long-term changes in sulfur compounds. The modeling system generally captures the long-term trends in nitrogen compounds, but does not reproduce the average seasonal variation or spatial patterns in nitrate. [ABSTRACT FROM AUTHOR]

Abstract: Under the 11th Five Year Plan (FYP, 2006–2010) for national environmental protection by the Chinese government, the overarching goal for sulfur dioxide (SO2) controls is to achieve a total national emissions level of SO2 in 2010 10% lower than the level in 2005. A similar nitrogen oxides (NOx) emissions control plan is currently under development and could be enforced during the 12th FYP (2011–2015). In this study, the U.S. Environmental Protection Agency (U.S.EPA)’s Community Multi-Scale Air Quality (Models-3/CMAQ) modeling system was applied to assess the air quality improvement that would result from the targeted SO2 and NOx emission controls in China. Four emission scenarios — the base year 2005, the 2010 Business-As-Usual (BAU) scenario, the 2010 SO2 control scenario, and the 2010 NO x control scenario—were constructed and simulated to assess the air quality change from the national control plan. The Fifth-Generation NCAR/Penn State Mesoscale Model (MM5) was applied to generate the meteorological fields for the CMAQ simulations. In this Part I paper, the model performance for the simulated meteorology was evaluated against observations for the base case in terms of temperature, wind speed, wind direction, and precipitation. It is shown that MM5 model gives an overall good performance for these meteorological variables. The generated meteorological fields are acceptable for using in the CMAQ modeling. [Copyright &y& Elsevier]

Abstract: This paper examines the impact of tripled anthropogenic emissions from China and India over the base level (gaseous species and carbonaceous aerosols for 2000) on air quality over the U.S. using the WRF/Chem (Weather Research and Forecasting – Chemistry) model at 1° resolution. WRF/Chem is a state-of-the-science, fully coupled chemistry and meteorology system suitable for simulating the transport and dispersion of pollutants and their impacts. The analyses in this work were focused on MAM (March, April and May). The simulations indicate an extensive area of elevated pollutant concentrations spanning from the Arabian Sea to the Northern Pacific and to the Northern Atlantic. MAM mean contributions from the tripled Asian emissions over the U.S. are found to be: 6–12 ppbv for CO, 1.0–2.5 ppbv for O3, and 0.6–1.6 μg m−3 for PM2.5 on a daily basis. [Copyright &y& Elsevier]

Abstract: The MM5/CMAQ system evaluated in Part I paper is applied to study the impact of emission control on future air quality over North Carolina (NC). Simulations are conducted at a 4-km horizontal grid resolution for four one-month periods, i.e., January, June, July, and August 2009 and 2018. Simulated PM2.5 in 2009 and 2018 show distribution patterns similar to those in 2002. PM2.5 concentrations over the whole domain in January and July reduced by 5.8% and 23.3% in 2009 and 12.0% and 35.6% in 2018, respectively, indicating that the planned emission control strategy has noticeable effects on PM2.5 reduction in this region, particularly in summer. More than 10% and 20% of 1-h and 8-h O3 mixing ratios are reduced in July 2009 and 2018, respectively, demonstrating the effectiveness of emission control for O3 reduction in summer. However, O3 mixing ratios in January 2009 and 2018 increase by more than 5% because O3 chemistry is VOC-limited in winter and the effect of NOx reduction dominates over that of VOC reduction under such a condition. The projected emission control simulated at 4-km will reduce the number of sites in non-attainment for max 8-h O3 from 49 to 23 in 2009 and to 1 in 2018 and for 24-h average PM2.5 from 1 to 0 in 2009 and 2018 based on the latest 2008 O3 and 2006 PM2.5 standards. The variability in model predictions at different grid resolutions contributes to 1–3.8 ppb and 1–7.9 μg m−3 differences in the projected future-year design values for max 8-h O3 and 24-h average PM2.5, respectively. [Copyright &y& Elsevier]

Abstract: The contribution of vehicular traffic to air pollutant concentrations is often difficult to establish. This paper utilizes both time-series and simulation models to estimate vehicle contributions to pollutant levels near roadways. The time-series model used generalized additive models (GAMs) and fitted pollutant observations to traffic counts and meteorological variables. A one year period (2004) was analyzed on a seasonal basis using hourly measurements of carbon monoxide (CO) and particulate matter less than 2.5 μm in diameter (PM2.5) monitored near a major highway in Detroit, Michigan, along with hourly traffic counts and local meteorological data. Traffic counts showed statistically significant and approximately linear relationships with CO concentrations in fall, and piecewise linear relationships in spring, summer and winter. The same period was simulated using emission and dispersion models (Motor Vehicle Emissions Factor Model/MOBILE6.2; California Line Source Dispersion Model/CALINE4). CO emissions derived from the GAM were similar, on average, to those estimated by MOBILE6.2. The same analyses for PM2.5 showed that GAM emission estimates were much higher (by 4–5 times) than the dispersion model results, and that the traffic-PM2.5 relationship varied seasonally. This analysis suggests that the simulation model performed reasonably well for CO, but it significantly underestimated PM2.5 concentrations, a likely result of underestimating PM2.5 emission factors. Comparisons between statistical and simulation models can help identify model deficiencies and improve estimates of vehicle emissions and near-road air quality. [Copyright &y& Elsevier]

Abstract: Today, parallel computers facilitate complex simulations of physical and chemical processes. To obtain more accurate results and to include multiple aspects of environmental processes, model codes of different scientific areas are coupled. An often used coupling strategy is to run the individual codes concurrently on disjoint sets of processors, as this keeps the codes mostly independent. However, it is important to improve the workload balance between the codes to achieve a high efficiency on parallel computers. In this paper, the parallel air quality model system LM-MUSCAT is presented. It consists of the chemistry-transport model MUSCAT and the meteorological model LM. Since an adaptive time step control is applied in MUSCAT the overall load fluctuates during runtime, especially at applications with highly dynamical behavior of the simulated processes. This causes load imbalances between both models and, consequently, an inefficient usage of the parallel computer. Therefore, an alternative coupling method is investigated. In this approach, all processors calculate alternately both models, whereby the load is distributed equally. Performance tests show that this “sequential” approach is well suited to increase the efficiency of coupled systems that have workload fluctuations in one or more models. In general, load variations can occur in models which use adaptive grid techniques or an adaptive step size control. Systems using such techniques can take benefit from the described coupling approach. [Copyright &y& Elsevier]

A gas-phase reaction mechanism for the atmospheric photooxidations of over 100 alkanes, alkenes, aromatic hydrocarbons, alcohols, ethers and other compounds representative of the range of reactive organics emitted into polluted atmospheres is described. Most of these organic species are represented using generalized reactions with variable rate constants and product yield coefficients for which individual assignments were made or estimated. This mechanism employs 19 species to represent the reactive oxygenated and organic nitrate products, and includes the gas-phase reactions of SO2, but does not include heterogeneous or liquid-phase reactions. The evaluation of this mechanism, by comparison of its predictions against the results of over 500 environmental chamber experiments, is described in a separate paper. This detailed mechanism can be used in assessments of relative atmospheric reactivities of organic compounds, and can provide the basis for the derivation of more condensed mechanisms for use in air quality simulation models. [Copyright &y& Elsevier]