# What controls the tendency of trace elements in different particle size fractions?

Trace element atmospheric particles are introduced from different sources, with both anthropogenic and natural origins.

By analyzing the concentration levels of 18 elements in samples of $PM_{2.5}$ and $PM_{10}$, the results showed that the size distributions of those elements are significantly different.

A number of papers explained that difference in size fraction of various species is related to their different sources.

Natural origin: the crustal element (i.e., $Al$, $Ca$, $Mg$) are always accumulated in coarser particles. Anthropogenic origin: the anthropogenic emissions ($Cu$, $Zn$, $As$, $Pb$) are always accumulated in finer particles.

I'm wondering if the chemical property of different species are important in determining their size distribution as well.

In other words, is size distribution not solely related to emission source (natural abrasion => coarse particles; anthropogenic combustion => fine particles)?

If so, what chemical properties would be essential to infer the tendency of the specific elements (into coarse particles or fine particle).

Any advice would be appreciated!

## PS

In previous research, I have found out one factor might be important:

Volatity

"The volatile elements (e.g., $As, Cd, Tl, Cu, Pb, Zn$) are strongly correlated across the size distribution and exist in the plume primarily as fine sulfate (0.6 mm diameter) with lesser amounts transported as coarse sulfates (3.5 mm diameter) and coarse chlorides (11 mm diameter)." copied from $\text{Martin et al., JGR, 2012}$

## 1 Answer

Crustal elements are essentially from soil which have undergone compaction during geologic processes. Particles are then lifted into the air (e.g. by wind) and coarse particles from the soil are suspended in the atmosphere. If the particulate is from wildfire, it is still of "natural origin", but the particulate is from a combustion source. Combustion creates fine particles.

Anthropogenic particulate emissions are dominated by combustion sources, because so much of our industry and energy production uses combustible fuels. Combustion creates fine particles. However, there are still several anthropogenic sources that create coarse particulate (e.g. road dust, construction dust, agricultural processes, etc.).

• Thanks for your answer. As you pointed out, it is important to emphasis that specific physics process (i.e., suspension, combustion) in the natural/anthropogenic origin. – Han Zhengzu Jan 12 '18 at 7:36