This study examines the effects of tariff reforms on air pollution across 232 Indonesian districts from 1993 to 2002, a time of rapid trade liberalisation. We construct a district level measure of exposure to tariff reduction, by combining the information on regional labour and production, and national input-output tables, with exogenous tariff reductions over three-year intervals. We also construct a representative and consistent measure of air pollution which covers almost all districts in Indonesia. Overall, we found that air pollution increased less in districts with greater exposure to input tariff reduction. Finally, we consider a variety of potential causal channels that may explain the observed relationships. The potential channels analysis supports the positive impact of tariff reform on air pollution through composition and technical effects.