Component of the difficulty in regulating this sort of ultrafine particles is that they are more challenging to measure and keep an eye on, demanding much more advanced and high priced machines. It wouldn't be feasible to established regulatory criteria that can not be monitored successfully, Prof. Kelly says. http://pearlthongsandknickers64838.collectblogs.com/23691710/5-tips-about-size-matters-you-can-use-today