Vertical distribution of ambient air pollutants (PM_2.5, PM₁₀, NO_X, and NO₂); A systematic review

Numerous investigations have explored variations in vertical air pollutant concentrations, yielding diverse findings. So, we have conducted this systematic review to gain a more comprehensive understanding of the vertical distribution of air pollutant concentrations (PM_2.5, PM₁₀, NO_X, and NO₂) and the influencing factors.

Relevant studies were identified by searching the three central electronic databases, PubMed, Web of Science, and Scopus, from the beginning of 2000 to the end of 2023. This study included original articles published in English that examine the pollutant concentration variations below 500 m.

Of 3614 articles, 57 studies met our criteria. Our findings showed a decline in PM_2.5 and NO_X concentrations as altitude increased, while NO₂ concentrations exhibited an increase. Conversely, no statistically significant relationship was identified between altitude and PM₁₀ concentrations. The regression analysis yielded coefficients for the relationship between concentration and altitude (0-500 m) as follows: PM_2.5 (-0.11), PM_2.5/PM₁₀ (0.0008), NO_X (-0.11), and NO₂ (0.13). Conducting additional research on this topic and investigating the impact of meteorological parameters on pollutant concentrations at different altitudes enhances our understanding of the vertical distribution of pollutant concentrations.