Sizes of atmospheric particulate matters determine the outcomes of their interactions with rainfall processes

Abstract

Environmental sustainability remains at risk, given the coupled trends of economic development with air pollution. The risk is even greater in the water-stressed world, given the potential suppression effects of air pollutants on rain formation. Here, since these suppression effects remain debated, we tested the hypothesis that air pollutants suppress rainfall in the water-stressed South Africa. This was done by fitting generalized linear models to a 21-year historical dataset of rainfall and air pollutants. We found that some gaseous pollutants and PM₁₀ show a significant negative correlation with rainfall, perhaps due to the temperature inversion they cause, which might prevent the upward rise of humid air and convective clouds to grow high enough to produce rain. Surprisingly, as opposed to PM₁₀, we found a rather positive significant effect of PM_2.5. Altogether, our study supports the hypothesis of rain prevention by pollutants but provides some nuances that are dependent on the size of air particle matters. To achieve environmental sustainability while growing the economy, we can only rely on emission purification technologies to strike this trade-off.

Figure 1

Rain quantity as a function of PM10. (a) For full year and (b) for only rainy season. Rain quantity is in mm.

Figure 2

Temporal dynamic of changes in PM10 and rainfall. (a) Full year and (b) rainy season.

Figure 3

Negative relationships between certain pollutants and rain occurrence using full year dataset. Rain occurrence is measured as presence/absence.

Figure 4

Geographic location of the study area (Vaal Triangle region) in South Africa. Map produced using ArcGIS Pro 2.9 (https://pro.arcgis.com/en/pro-app/2.9/get-started/get-started.htm).