Greenpeace probe into SA pollution

MOGESH Naidoo, lead air quality modeller at the Council for Scientific and Industrial Research (CSIR), says concerns previously raised by experts about Greenpeace’s three-month satellite data analysis still stand.

“It is very difficult to estimate ground concentrations and emissions via satellite,” says Naidoo. “Greenpeace also have Eskom emissions data so I’m not sure why they want to go a round about way to derive them from satellite data; unless they are trying to verify the Eskom data.”

Coal-fired power plants are not the only source of NOX (nitrogen oxide) in Mpumalanga.

“This is still relevant considering Sasol presence. Combined, vehicles emit a large amount of NOX, however, this is over a larger area. The issue with vehicles are in your face as opposed to industries with tall stacks (which could also impact areas nearby).

“That’s why air quality management is applied to more than just one source, because it is the ambient atmosphere and its constituents you are ultimately trying to manage, by pulling levers at different emission sources.

“There is a lot of interplay between sources and their contributions, which cannot be ascertained from just one source of information.”

The five ambient air quality monitoring stations in the Highveld Priority Area measure NOX concentrations far below the ambient air quality standard. “This is because the stations monitor at the surface, while much of industrial stack pollution ends up in the free troposphere. Tropomi captures this upper air pollution, but may under-estimate the surface levels.

“My stance on the satellite analysis is that the Highveld region is indeed very polluted. Eskom emits very large quantities of NOX and SO2.

“Ranking the region is very subjective, and attributing the ambient air quality (at the surface) to a single source using satellite data has many uncertainties currently to make conclusive statements.

“The power stations definitely do emit a very large amount of NOX and SO2, however what reaches the surface when, where and how much is a bit uncertain right now. Their plumes could be intermittently reaching the surface at places where there aren’t monitoring stations.

“The modelling work at CSIR is aiming to answer these questions.”

Naidoo says Greenpeace’s model results are reasonable, except for PM2.5 air quality reports which look high.”

Greenpeace’s health impacts study is a major improvement over the last.

“Eskom (and other sources in the Highveld) definitely impact human health in the region.

“We’re completing the Highveld health study so those results should be compared to Greenpeace’s results.”