Environmental concerns are increasingly being incorporated into regional trade agreements (RTAs) to promote environmental quality and ultimately ensure compatibility between trade and environmental policies. This occurs in a context where air pollution and its effects on human health are of major concern. This paper investigates whether the proliferation and depth of environmental provisions (EPs) in RTAs are associated with lower concentration levels of particulate matter. We present an index of EPs in RTAs that measures the breadth and depth of the provisions and use it to estimate the effect of ratifying RTAs with different levels of EPs on changes in PM 2.5 concentration levels in a panel of OECD countries over the 1999-2011 period. Using an instrumental variables strategy, we find that countries that have ratified RTAs with EPs show lower levels of PM 2.5 concentrations when we control for scale, composition and technique effects and for national environmental regulations. Moreover, the PM 2.5 concentration levels in the pairs of countries that belong to an RTA with EPs tend to converge for the country sample. The results also hold for a longer period of time and a broader sample of 173 countries as well as for other pollutants, namely CO 2 and NO 2 .succeeded in integrating environmental issues in multilateral trade negotiations 1 , usually leaving these issues to environmental multilateral agreements (MEAs). Until now, MEAs have been focused on particular aspects related to global (e.g. Kyoto) and local climate change (Montreal Protocol), or conservation and biodiversity (CITES), among many other issues. However, their effectiveness is far from being generally recognized 2 .An increasing number of recently ratified RTAs have introduced environmental provisions (EPs) in the main text of the RTAs or in accompanying side agreements.These provisions aim to protect the environment and establish methods of collaborating on environmental issues (Morin and Jinnah, 2018;Yoo and Kim, 2015).The breadth and depth of the provisions vary widely by agreement. At a minimum, new RTAs tend to incorporate environmental issues in the preamble or in some articles dealing with investment issues or exceptions. Other RTAs include a chapter dedicated exclusively to environmental matters, whereas in some cases, environmental aspects are covered in a side agreement 3 . This paper advances the current status of the literature body on the nexus of international trade, trade agreements and the environment in two fronts. First, by categorizing RTAs according to the breadth and the depth of the EPs included in the RTAs or in the corresponding side agreements. This categorization is new 4 , theoretically reliable, replicable and justifiable and is used to further investigate the effects of trade agreements on environmental quality. Second, we focus on the effect of RTAs with EPs on PM 2.5 5 population weighted concentrations and explore whether the inclusion of most comprehensive EPs in RTAs is associated with higher air quality in th...