Figure 3 . An action plan toolbox to prevent and mitigate air pollution effects on childhood asthma

Industrial activities and traffic related air pollution

The design of sustainable cities and the evolution of environmental conditions are two of the main future challenges to strengthen urban resilience and sustainably. One promising approach to achieve these challenges is to implement nature-based solutions (NBS) in the management and design of urban areas. NBS can provide several benefits to cities and address different societal challenges, including air pollution, while also contributing to restoring biodiversity, improving human health, and thus supporting community wellbeing and livelihoods. NBS, including indoor plants in living rooms and workplaces, trees in streets and parks, green roofs and green walls, urban forests, and green infrastructures, could be effectively implemented as an economic and sustainable solution to reduce exposure to air pollution. Pollutants may be removed from the atmosphere through wet and dry deposition on the tree surface as in the case of particles, and/or by stomatal adsorption and absorption processes in the case of gaseous pollutants. The identification of specific plant species based on their air pollution tolerance index, physiological characteristics, and habitat may be helpful in the mitigation of air pollutants from different to a greater extent. The BRIDGE project demonstrated that increasing canopy cover by between 20% and 30% could improve PM10 removal in a range of 3% by the year 2050 (www.bridge-fp7.eu). Recently, and within the framework of the GreenInUrbs project, the “Specifind ” tool has been developed to support NBS by allowing the selection of the best tree species based on several parameters, including the improvement of air quality (http://www.greeninurbs.com/p_specifind/).
The European Union (EU) has been making efforts to reduce pollutant emissions from industrial sources, mostly by applying legal regulations, such as the EU Emissions Trading System and the Industrial Emissions Directive [79, 80]. Data submitted to the Convention on Long-range Transboundary Air Pollution by the associated Nations, and published by the European Environment Agency (EEA), shows that the concentrations of industrial emissions have been tendentially decreasing since 1990 (Figure 4 ), suggesting that these regulations can indeed be potential solutions to mitigate the effects of industrial pollution [81].