 (1 0 .0 7) C (7 .9 4 ) I (3 .8 8 ) C (5 .1 7) C (6 .9 4 ) I (3 .8 3) C (7 .7 9 ) C (6 .9 6 ) I (4 .1 9 ) C (4 .9 2) C (7 .1 1) C (4 .9 8 ) I (2 .9 3) C (1 1. 9 5) * , ** , an d ** * re pr es en t st at is tic al si gn ifi ca nc e at 10 ,5 ,a nd 1% ,r es pe ct iv el y Bo un d te st : "C " = C oi nt eg ra tio n, "I " = In co nc lu si ve ," N C " = N o C oi nt eg ra tio n, th e Fst at s is sh ow n in pa re nt he se s (s ee T ab le C fo r up pe r an d lo w er bo un d cr iti ca l va lu es ) ARTICLE PALGRAVE COMMUNICATIONS | https://doi.org/10.1057/s41599-019-0369-8 8 PALGRAVE COMMUNICATIONS | (2019) 5:156 | https://doi.org/10.1057/s41599-019-0369-8 | www.nature.com/palcomms might be the result of insufficient pollution monitoring policies due to the changing industrial structure in Kitakyushu city might be an explanation for the increasing dust emission as firms grow larger. To elaborate, it is reported that there is a rising number of large firms in iron steel, chemical, and automobile sectors, etc. who have outsourced their activities to smaller firms receiving many incentives and less stringent regulation and inspection from the government (OECD, 2013). In terms of Ox emission, even though it is closely related to the concentration of NO2 in the atmosphere, it is still very difficult to control as Ox emission is created through a complex photochemical reaction of NO2 with other substances in the air (Guderian, 1985). Relationships between road infrastructure development and air pollution emissions. Our ARDL analysis finds that building more high-quality roads, in particular-paved road, corresponds to the decline of dust emission (βlnRoad=−0.361, p-value < 0.05), CO emission (βlnRoad=−0.357, p-value < 0.1), and the increase of the NO2 (βlnRoad= 0.341, p-value < 0.05), Ox emissions (βlnRoad= 0.347, p-value < 0.01) (see Table 2). The results of NARDL analysis also confirm the relationships between road infrastructure development and air pollution emissions (see Fig. 3). However, in all NARDL models, while the