The leaves from different locations revealed variations in particle concentrations and sizes. Additional analysis of the elemental composition of particles showed differences which could be related to not only urban and rural location but also to proximity to roads and traffic patterns. The hypothesis suggesting smaller particles would be found on rural leaves than on urban leaves was confirmed.

The most striking differences between leaves were found on leaves rinsed by rainfall or by artificial rinsing. The particle concentrations were shown to decrease dramatically with rinsing, as did average particle size. The average percentage of Ca in particles, a major element on non-rinsed leaves, was also shown to decrease dramatically with rinsing.

The aerosol filter samples had similar average particle diameter ratios between urban, suburban, and rural samples as leaf samples. However, the overall average diameters on the filter samples were smaller than those on the leaves. This shows one of the differences between filters and leaves – that filters collect smaller particles more efficiently than leaves due to their independence of sedimentation, while leaves rely on sedimentation.

The difference in composition observed between particles on leaves vs. those on filters may be due to interaction of the particles with the leaves as well as moisture, and the difference in diameters of particles collected. These observations indicate, for example, that leaf sampling may not be ideal for detection of a major aerosol particle, fine sulfates, which are readily detected on filter samples. However, the leaf samples do seem to reflect the larger Ca and S containing particles more prevalent in the highly-trafficked urban or suburban areas. The disadvantages of the leaves over filters may be offset by the prevalence of potential samples, as well as the potential for long-term integrative sampling. Leaves could be used for indoor sampling, where the effects of precipitation would not be a factor. The interpretation of all these parameters is very complex and warrants further research by myself and others.

This research shows that leaf sampling can very likely be used as a method for investigating the complex problems of particulate air pollution, as long as the many variable factors are considered.