Catálogo de publicaciones - libros

Controlling ground level ozone, a relatively recent problem but now pervasive in many urban centers, requires linking knowledge about its formation (science) to choices society makes about present and future economic development and social behaviour (policy). But the future is unknown and can follow many courses, and so future air quality is inherently unpredictable and modeling it an inexact exercise. Uncertainties about the future and the complexity of ozone formation also present a tension for modelers: on the one hand, a model is needed that is sensitive to the intricacies of meteorology, photochemistry and emissions while on the other hand a model is needed that can be used to investigate many possible futures. This tension leads to a spectrum of modeling techniques: at one end are comprehensive Eulerian grid models, such as Models-3/CMAQ (EPA, 2004), which represent the most complete way of describing ozone formation, but due to their complexity and costs, preclude examining large numbers of possible futures; and at the other end, less exact models having quick execution times, like the SOMS model (Venkatram, 1994), containing many approximations but nonetheless include the main processes in ozone formation.

High O3 episodes are observed in several eastern US national parks, among which the Great Smoky Mountains National Park by far of the fastest increase in frequency of exceedance days (days when any 8-hour average O3 concentration exceeding 85 ppbv). It has been well established that the southeast US rural areas are characterized with strong biogenic VOCs emissions and that O3 production in this region is mostly NOx-limited during summer time. Thus, understanding the contribution of nitrogen oxides to O3 formation during transport and for local photochemistry is essential to predict what effects the planned reductions in NOx emissions from large point sources might have on observed O3 concentrations at these southeast national parks. Our specific interests in this study are: 1) to quantify the relative importance of point sources and mobile sources to total nitrogen oxides emissions; 2) to identify origins of air masses associated with high levels of nitrogen oxides and O3; 3) to quantify contributions of individual chemical and physical processes, i.e., chemistry, transport, emission, and deposition, to the budget of production and removal of nitrogen oxides and O3 in the southeast national parks.

Urban ozone is a major pollutant produced by various sources as well as urban traffic through photochemical transformation of nitrogen oxides, carbon monoxide, and volatile organic compounds. Ozone pollution in urban areas is a complex problem involving both atmospheric diffusion processes, chemical reactions and transport. The superimposition of chemical production and physical processes leads to episodic level of photochemical air pollution under favorable meteorological conditions and abundance of precursors. The air quality of Istanbul has been a major concern since the early 1980s. The city has experienced several air pollution problems in 1980s. Usage of poor quality lignite was banned in late 1993. The fuel switching from coal to natural gas has gradually improved the air quality (Topcu et al., 2003). Today SO2 and TSP levels are below the national air quality standards. However, a new air pollution type has appeared in Istanbul that is the photochemical pollution. Surface ozone concentrations are increasing in the city depending on increasing numbers of cars that use mostly gasoline and poor dispersion conditions. Ozone episodes are frequently observed when anticyclonic pressure systems are in the vicinity of Istanbul.

The main problem in forecasting urban air pollution is the prediction of episodes with high pollutant concentrations in urban areas, where most of the well-known methods and models based on in situ meteorological measurements, fail to realistically produce the meteorological input fields for the urban air pollution (UAP) models. UAP models in operational urban air quality information and forecasting systems, as a rule, use simple in-situ meteorological measurements which are fed into meteorological pre-processors (Fig. 1, dash line). Lacking an adequate description of physical phenomena and the complex data assimilation and parameterisations of numerical weather prediction (NWP) models, these pre-processors do not achieve the potential of NWP models in providing all the meteorological fields needed by modern UAP models to improve urban air quality forecasts.

This study describes the application of atmospheric modelling to assess transboundary transport from the USA and the influence of natural emissions sources for the 12 most populated sub regions across Ontario, Canada. The impact of Ontario emissions was determined by the difference between model runs including all emissions and model runs with Ontario’s anthropogenic NOx, SO2, VOC and primary particulate matter emissions shut off. The modelling has been done for the entire May through September 1998 period. Since there were many days with high ozone and/or high PM2.5 that summer, the model runs provide estimates of the variations in Ontario’s impact from episode to episode and from the spring to the summer.

Beyond the associated harm to human health,1 non-attainment of air quality standards can substantially hamper the economy of a region2 and its access to federal funds. The costs of emissions control are substantial as well and vary greatly among various options. Thus, much is at stake in reducing air pollution in a costefficient manner. Alternative goals can be considered in the optimization of air pollution control strategies. The development of regulatory attainment plans can be abstracted as a constrained optimization problem of attaining air quality standards at minimal cost. One may also consider how to minimize regional pollutant concentrations or potential population exposure subject to a budget constraint. Because ozone forms from complex nonlinear interactions involving nitrogen oxides (NOx) and volatile organic compounds (VOC),3 the impact of a control measure will depend on which pollutant is reduced, the location of reduction, and variable factors such as meteorology. Thus, ozone sensitivity must be considered along with cost in evaluating cost-effectiveness.

Road traffic is widely recognised to be a significant and increasing source of photochemical pollution precursors. EU Directives in force up to 2010 require substantial NOx and VOC emission decreases. Such reductions can improve or further deteriorate air quality because of the emission mix and the photochemical regime characterizing the area under study. The comprehensive modelling system GAMES (Gas Aerosol Modelling Evaluation System) (Volta and Finzi, 2004) has been used to evaluate the seasonal impact of the EU Directive abatement strategies on road traffic emissions in Northern Italy. In this area frequent stagnating meteorological conditions and elevated Mediterranean solar radiation, associated with critical anthropogenic emissions, regularly cause high ozone level episodes, especially during summer months. Several experimental campaigns (Vecchi and Valli, 1999), (Neftel et al., 2002) as well as modelling studies (Silibello et al., 1998), (Baertsch-Ritter et al., 2003), (Gabusi and Volta, 2004) have been carried out to investigate photochemical pollution in such complex domain.

This paper discusses simple risk-based ways of choosing locations where reductions in airborne emissions should be made, based on exceedences of environmental objectives. A major regulatory issue is how emissions should be managed within national emission limits, at the same time minimising exceedences of environmental objectives. As air quality models become more detailed, complex environmental optimisation becomes harder to manage. At the same time decisions involve other qualitative factors besides meeting air quality standards alone. In this paper a practical method is introduced for dealing with the risk posed by acid and nutrient deposition and exposure to particles based on describing the source-receptor relationship in terms of a Green’s function. The aim of the research is to produce a map (or maps) showing the relative importance of source locations for emissions from a specific type of source. The method allows one to decide where would be the best place to reduce current emissions. The examples are chosen to illustrate the approach to environmental decision making and in later examples show how social/demographic factors may be taken into account.

Compact and polycentric city forms are associated with minimal consumption of land and energy, and are often promoted as the more sustainable and hence preferred mode of urban development. In this context, a series of numerical simulations was performed to evaluate the impact of two urban development scenarios on air quality and related human exposure. The area that was selected consists of a highly urbanised region in the Ruhr area, located in the north-western part of Germany in central North Rhine-Westphalia with a total population in excess of 5.5 million. The choice for this particular area was mainly motivated by its size and importance, as well as its conversion potential. Two distinct scenarios were selected. The first is referred to as ‘urban sprawl’ and is characterized by a significant increase in built-up surface. This scenario supposes a continuation of the current process of people leaving the highly occupied central part of the study area to settle in the greener surroundings. In the second scenario, referred to as ‘satellite cities’, persons and jobs were displaced to five existing towns located near the core of the urban area. Models dealing with land use, traffic flows, and atmospheric dispersion were applied, first under conditions representative of the urbanised area as it is today. Subsequently, the urban development scenarios were implemented using spatial modelling techniques, and the impact of the scenarios with respect to air quality was evaluated, including an estimate of human exposure to air pollution and the associated external costs.

The U.S. Environmental Protection Agency is examining the concentrations and deposition of air pollutants that are known or suspected to cause cancer or other serious health effects in humans. These “air toxics” or “hazardous air pollutants” (HAPs) include a large number of chemicals, ranging from non reactive (i.e. carbon tetrachloride) to reactive (i.e. formaldehyde), exist in gas, aqueous, and/or particle phases and are emitted from a variety of sources. Some HAPs, such as formaldehyde and xylene, also play an important role in the production of ozone and particulate matter. In addition, concentrations of air toxics are required over both shorter (days) as well as longer (a year) time scales in order to analyze health risks resulting from exposure to these compounds. These requirements challenge the current capabilities of numerical air quality models beyond their needs for other pollutants, such as ozone.