Hard Coal Fly Ash and Silica-Effect of Fine Particulate Matter Deposits on Brassica chinensis

Problem statement: One focus in recent atmospheric pollution research is on fine Particle Matter (PM), especially as result of increasing traffic and anthropogenic activity in urban areas. Here, the impact on animal and human health has been in the center of many studies. Despite the fact that PM depositions can affect plants on the long term, there are only few studies about the impact on plants conducted. Approach: Therefore we studied the impact of PM on plants, using naturally occurring silica dusts (diatomaceous earth) and hard Coal Fly Ash (CFA) from burning processes. Dusts were applied onto Brassica chinensis L. using a simple duster (covering upper leaf surfaces) or electrostatically (covering leaf upper and -underside). Results: Main components of the tested CFA are SO₄^2-, K, Ca and NH₄₊. The pH value of eluates was found to be around 9.5 in CFA and 5.7 in silica. B. chinensis was insensitive towards the high pH and showed no growth reduction when grown in silica or CFA substrate. PM deposition on leaf surfaces results through shading in a reduced photosynthetic activity. The reduction is relatively higher at higher light intensities. Photosynthesis stays reduced after removal of silica PM from leaf surfaces. We assume that stomata get cloaked by small particles and that silica absorbs lipids from the epicuticle resulting in a general stress reaction. Smaller sized silica particles resulted in a higher reduction of CO₂-absorption. Next to particle size is the photosynthesis negatively correlated with exposure time for silica PM. The chlorophyll fluorescence data indicate that dust-covered leaves exhibited significantly lower quantum yield of PS II and a reduced quantum efficiency of PS II and therefore supported the gas exchange data. Conclusion: Reduced photosynthetic performance would be expected to reduce growth and productivity of B. chinensis. In contrast to silica hard coal fly ash showed only a reduction of photosynthesis through shading but did not have any long time effects after washing them off.