There are some studies that have suggested that greening of highly polluted streets can significantly reduce pollution, but there is little validation of this research and numerous other studies have not supported this idea. Overall, these solutions are too small compared to the magnitude of the problem and can, in certain circumstances, make things worse. Trees planted along roads can limit the dispersion of pollutants away from the roadside and certain plants are high emitters of volatile organic compounds during the summer months that contribute toward ozone generation. However, it is a politically appealing solution, because it provides an apparent alternative to targeting and legislating against the polluter/vehicle owner. There are many other benefits of greening the environment, but the potential impacts on urban air quality have been overstated.