The expansion of industrial and construction sectors, rapid growth in urban population and the increased use of motor vehicles is contributing to increasingly poor-quality air in major cities, including in Cambodia. To tackle this problem, this policy paper proposes the idea of ‘Green Friday, ’a social movement campaign which aims to reduce the air pollution in Phnom Penh by encouraging people to use green transport beginning with one day a week by using a motivational intervention called ‘Avoid-Shift-Improve-Reward’.