Fig. 5: Research attention and influencing factors in different regions.

a Country-level distribution of the most frequently studied air pollutant, categorized by World Bank income group classifications. Color shading indicates the predominant pollutant of research focus in each country, while black denotes countries with insufficient data (fewer than three publications on the top pollutant), highlighting critical research gaps. High-income countries tend to focus on O₃, whereas upper- and lower-middle-income countries primarily focus on PM. Many low-income countries lack sufficient research to identify a dominant pollutant. b The Research Attention Degree Index (RADI), standardized on a scale from –1 to 1, quantifies the relative sufficiency or deficiency of research activity across countries, adjusted for population size. Higher RADI values indicate relatively more research attention. c Correlation analysis between RADI and selected factors, including socioeconomic indicators (e.g., GDP per capita), climatic variables (e.g., temperature and precipitation), and pollution metrics (e.g., average PM_2.5 exposure). A strong positive correlation is observed with GDP per capita, while pollution exposure and health risk show inverse correlations, revealing a potential imbalance where more polluted regions receive less scientific attention.