Convergence analysis of ammonia emissions by sector and fuel source in OECD countries from 1750 to 2019 using a new Fourier-centric wavelet approach.

Although ammonia emissions are not as huge as carbon and methane emissions, they pose significant threats to ensuring environmental sustainability and productivity. However, the existing literature has paid less attention to the underlying characteristics of ammonia emissions. The chief target of this study is to investigate the stochastic convergence of ammonia emissions at the aggregate level, by sector, and by fuel source in 37 Organization for Economic Cooperation and Development countries for more than two centuries of data. Using a newly proposed Fourier-augmented wavelet unit root test, the empirical findings reveal that the relative ammonia emissions series in most Organization for Economic Cooperation and Development countries follow the unit root process in the aggregate, sectoral, and fuel-specific analyses. Therefore, these findings refer to the existence of divergence, while stochastic convergence does not exist in most cases. Having a divergent pattern of ammonia emissions has several policy implications for policymakers in the context of environmental sustainability. (i) Relative ammonia emission cannot revert to its steady-state path without policy intervention, (ii) policymakers have a chance of affecting the dynamics of ammonia emissions in Organization for Economic Cooperation and Development countries. (iii) As a policy response, the study recommends the pursuant of national environmental policies with consideration to the unique characteristics of the individual countries as the non-existence of convergence of environmental series could result in a diverse level of consciousness of environmental degradation among countries with divergent patterns on emissions levels.