Average NOx concentrations are also high in Chinese cities, at around the WHO guideline limits of 40 pg/m3, averaged over one year. Moreover, as noted above, NOx emissions have risen in recent years and this is reflected in the air quality of cities where average NOx concentrations rose over 5% between 2005 and 2010. In Beijing, over the whole winter of 2007/08, NOx pollution averaged seven times the WHO hourly guidelines, with mobile sources accounting for almost two-thirds thereof.