The concentration of some air pollutants has decreased over the past decade, but air quality is still poor (see Chapter 1). The key driver for air pollution in cities is on-road transportation, which continues to be a primary mode of urban transport34 in Chile. National air-quality regulations were updated for a number of air pollutants (PM2.s S02, NO, HC and CO), and a “Clean Air Programme” was launched in 2010, aiming to improve air quality in the biggest cities through sectoral emission reduction strategies (e.g. firewood, industries, transport and monitoring).