Weakening the Case for Urban Tree Planting

A nonprofit organization focused on environmental preservation recently argued that planting trees in urban areas will significantly reduce greenhouse gas emissions. The organization stated that trees absorb carbon dioxide, thus helping to mitigate climate change. They also claimed that increased greenery would improve air quality and enhance the overall well-being of city residents. However, a local business group countered this argument by citing that simply planting trees might not be enough to address the complex issue of urban air pollution.

Which of the following, if true, would most seriously weaken the nonprofit organization's argument?