Visualizing Patterns and Differences in Fine Particulate Matter(PM_2.5) Research Between the USA and China over Last 25 Years: A Bibliometric Analysis

To reveal patterns in scientific research results and compare differences in studies on fine particulate matter (PM_2.5) between China and the USA, 6608 publications from 1992 to 2016 were collected from the Science Citation Index Expanded （SCI-E）databaseandanalyzedbybibliometrics.Histcite^TM, Bib Excel1.0.0.0, Net Draw and VOSviewer were used for statistical and visual analysis during this study. Publication outputs, journals, institutions, authors and author keywords were all analyzed to identify publication patterns, research hotspots and research trends. Based on this study, the number of publications produced in future years is expected to be at least twice that in 2016. The number of publications in China and the USA increased annually from 1992 through2014, promoted by improved social and economic conditions. Gross domestic product （GDP） was significantly positively correlated with the number of annual articles published in China and the USA （p＜0.05）. Through comparative analysis, it was observed that the output of publications in the USA before 2014 was larger than that in China. The total output of PM_2.5-related publications in China increased rapidly and far exceeded that in the USA after 2014. It is predicted that the leading region for research on PM_2.5 in the future would be China. Analysis of author keywords indicated that"chemical composition"and"source allocation"were the main research hotspots in China and the USA. This research on exposure would be valuable in the future because of the pollution problem in China.Moreover, patterns and differences in scientific outcomes were revealed in this study and this study might provide potential guidelines for future research and management.