Question

vegetation has two primary mechanisms by which it reduces air pollution: deposition (absorption of pollutants) and, the more effective, dispersion (dilution of pollutants by ventilation). accordingly, establishment of green space to reduce major air pollutants such as coarse particulate matter in urban areas receives considerable attention. research by zander s. venter et al. comprised data from air - quality monitoring stations in belgium, the us state of west virginia, and thousands of other global locations over a ten - year span, coupled with aerial imagery of those locations from the same period. the researchers ultimately recommended that reducing anthropogenic emissions remain the primary focus of urban air - quality improvement efforts.
which finding from the study, if true, would most directly account for the recommendation by venter et al.?
a) the association between levels of coarse particulate matter and green space is strongly negative for locations containing or in close proximity to major cities but becomes insignificant for more rural locations.
b) the association between green space and coarse particulate matter levels is moderately negative overall but becomes slightly negative and sometimes positive when consideration is limited to busy streets with tree cover heavy enough to hinder ventilation.
c) ambient levels of coarse particulate matter are comparable across locations with comparable local infrastructure (e.g., typical building shape) but vary considerably depending on the predominant type of vegetation present.
d) there is a predictable relationship between a locations typical climate conditions and the efficacy of green spaces in that location, but anomalous local weather events have an outsized effect on deposition and dispersion of coarse particulate matter.

Explanation:

The recommendation is that reducing anthropogenic emissions should be the primary focus. Option B shows that the negative association between green space and coarse particulate matter (which is an air pollutant) is not strong in busy streets (where anthropogenic emissions are likely high). This implies that green space alone may not be enough to combat air pollution in areas with significant anthropogenic emissions, thus supporting the recommendation to focus on reducing those emissions.

Answer:

B. The association between green space and coarse particulate matter levels is moderately negative overall but becomes slightly negative and sometimes positive when consideration is limited to busy streets with tree cover heavy enough to hinder ventilation.