Report on climate change and air quality interactions

The main objective of this report is to layout a broad overview of the latest understanding of climate and climate change and its connection with urban air quality. It critically reviews recent research studies that are not yet being used in practical applications and that are critical for later implementation of Passive Control Systems (PCSs) within the iSCAPE project. The Introduction is devoted to review the broad motivation for reducing air pollutant concentration in cities; it also deals with the potential benefits of using climate change information for city planning, a topic that is at the core of the iSCAPE project. The report is organized in two main parts, described as follows. 1. Climate and climate change in European cities 1.1. Description of climate change modelling approach. The study is performed starting from the regional to the urban scale. Issues to be kept in mind when monitoring the impacts of global climate change on urban and smaller scales are data quality and homogeneity; climate conditions in cities may not be captured by weather stations, as these are typically located in open vegetated land (rural or natural landscapes). Moreover, uncertainty is always involved in climates change projections. For simulations of future climate, climate model experiments are run under assumptions about the future evolution of atmospheric composition, land use change and other driving forces of the climate system. Global and regional climate models, typically having a grid size of tens of kilometres or larger, poorly resolve the urban land surface. The geographical pattern of the simulated climate response may be downscaled using various methods. Several physical-based surface models can simulate air-surface interactions at a horizontal scale of about 100 metres. However, many urban parameterizations still follow highly simplified approaches. The Town Energy Balance (TEB) model (Masson, 2000; Lemonsu et al., 2004), included in the surface interaction model SURFEX, is an example of a model capable of clearly separating buildings, air within urban canyons, roads, and, if present, trees, gardens etc. 1.2. Setting of the role of physical variables in current climate and change. The focus is to set the basis for subsequent studies within iSCAPE. The role of the physical variables that can be extracted from future climate change scenarios at urban scale is discussed. These variables are those that are relevant for establishing the link between climate change and air quality i.e. temperature, wind speed, pressure and solar radiation, and these variables have to be used to evaluate the efficacy of PCSs in future scenarios. This is also one of the main aims of iSCAPE. The main results from this sections are: 1.2.1. the observed annual-averaged pan-European temperature trend of 0.179\ub0C per decade since 1960. 1.2.2. the average impact of urbanization on that trend is 0.0026\ub0C per decade since 1960. The effect is strongest in spring and summer. 1.2.3. Among the iSCAPE cities, the projected summertime warming is largest for Bologna and smallest in Dublin. In winter, and also in spring and autumn, the most pronounced increases in temperature are likely to take place in Vantaa. 1.2.4. Precipitation is generally projected to increase in winter and decrease in summer. However, the sign of the change is uncertain in Bologna in winter and in Vantaa in summer. 1.2.5. Incident solar radiation and diurnal temperature range are projected increase in most of Europe in spring, summer and autumn. 1.2.6. The observed reduction in the mean annual solar radiation in southern Finland over the period from 1958 to 1992 was mainly attributed to a pronounced increase in cloudiness, with only a minor contribution from the direct effects of the relatively large aerosol load at that time. 1.2.7. Wintertime sea level air pressure is projected to decrease in Vantaa and increase elsewhere. In Dublin and Guildford, the projected trend is positive in all seasons and in Belgium and Germany in all seasons except for the summer simulations. 2. Air quality and climate change interaction in European cities 2.1. Focus on the mean state of pollutants in the target cities. This part magnifies the focus on the mean state of the main pollutants (NO2, PM10 and PM2.5) as well as O3 that is relevant for climate change for the iSCAPE target cities. Given that, the scope is to identify the preferential conditions for PCSs deployment in each target city and provide state of art knowledge for subsequent work packages (WPs). Specifically, we find that pollutant concentrations have different impacts due to meteorological, geographical and structural features of the single city, but also as a result of local air quality policies. In general traffic-induced emissions (NO2 and PM10) have an influence on total concentration at street level, but not at urban scale. Residential heating systems also contribute again at street level, but its signal is weaker. Two pollutants, NO2 and PM10 have a dependence on emissions at the street scale, while PM2.5 is more homogeneous in the urban environment. Concerning the risks on human heath connected to exposure to high level of PM2.5 has led to a decrease and an adjustment of concentrations at WHO suggested level for human health which is stricter than the European limit. Only Bologna, among the target cities requires to improve its efforts to mitigate the PM2.5 concentrations. Ozone concentrations is quite homogeneous at the city scale. In rural areas ozone concentrations sensibly grow, supported by favourable conditions. 2.2. Assessments on pollutants linkages with climate change. Really few studies have been performed on the relationship between air quality and climate change, especially at small scales. It easier to find studies concerning air quality linked with the urbanization growth (with some problems of inhomogeneity between different nations due to different necessity and city types). At European scale, the climatological variables that mostly affect air quality are: surface temperature, precipitation and sea level pressure. Temperature scenarios, coupled with precipitation pattern projection, facilitate an increase in pollutants such as ozone due to increased biogenic emissions and photochemical rates and reduced wet removal. Changes in meteorological variables can modify global sea level pressure patterns, with consequences on local circulations and distribution of air masses. In the end, climate change induced by enhanced pollutant emissions will in turn increase pollutant concentration. So, a positive feedback is established, leading to an intensification of climate changes in those regions highly affected by pollution. It is important to underline that these connections between climate and pollutants concern the larger scales (global, or at least European). Specific studies at local scale have to be provide to achieve a better understanding on the future livability of our cities