The air quality in Hong Kong compares well to that of most major cities in the industrialized world and is far better than in most developing countries. In particular, the pollutants which are attributable to motor vehicles - carbon monoxide, hydrocarbons, nitrogen oxides and particulates - are not evident in high concentrations by international standards. There are two exceptions: (1) in heavily congested urban corridors levels of particulates and nitrogen oxides reach high levels, and (2) in tunnels and carparks, carbon monoxide levels frequently exceed EPD standards.