Based on multiple site sampling of airborne $PM_{2.5}$ and $PM_{10}$ , the elemental concentrations of the trace elements were analyzed.

I have found out in the site near surface coal mining zone presenting ~3-4 times of heavy metals ($As$, $Cd$ and $Pb$) compared to those of in other sites (~ 50 km away from the coal-production zone).

The receptor-oriented source apportionment tool was also applied, with a special factor could be identified which has high loading of element Cd, As, Pb.

Therefore, I infered that this factor might be attributed to coal mine dust. Since Zn, Cd, Pb were all existed in coal seams as some minerals and they can be emitted in the coal mining, transportation activities.

Since there have been none similar research pointing out this factor, I was doubt about the rationality of my judgement.

More detailed description are depicted as follows:

(1) This factor was only show apperaent contribution on the site near coal mine area

(2) This factor can be produced in PMF analysis for both $PM_{2.5}$ and $PM_{10}$ samples, respectively. If I removed the dataset of the corresponding site, this factor will be gone in the source identification analysis.

Some "negative" information:

(1) The wind direction factor was also implemented. The source variability was not well in accordance with the wind field (As expected, the high contribution of coal mine dust should occurs in the time when the wind is coming from the direction of coal mining area)

(2) Combining with a prior knowledge, the source profile for coal mine dust (upper soil by wind-blown process) should enriched in coarse particles, while the high proportions of $As$, $Cd$, $Pb$ in $PM_{2.5}$/$PM_{10}$ were still founded in the coal-mining site.

The figures followed was the emission features of coal combustion and "coal mine dust"(inferred by myself).

enter image description here

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I am not well satisfied with my interpretation on the apportionment results. I will be grateful if some researchers shed some light on this issue.

More information on the sampling sites

PM samples are simultaneously collected in six sites within the studied area in daily basis. As a energy base area, there are 8 coal-fired power stations within this area.

Site 1 was located near coal mine as the following figure.

enter image description here

More information on the source identification.

One factor can be identified in all sites, with high mass loading of Na, Cr, As, Zn, Pb. These trace elements existing in coal can be volatilized in high temperature combustion processes and then coagulated into solid phase in atmosphere.

The seasonal variability of this factor also show the trend of highest contribution in winter. It might indicate the increasing coal combustion for domestic heating which is common in north China.

Thus, I inferred this factor was the emission from coal combustion (coal-fired power/heating plant and domestic uses of bulk coal).

The other factor which was similar with the factor in the source profile. High mass loading of As, Cd, Pb was also founded. Meanwhile, this factor presented elevated contribution only at the site near surface coal mining zone.

Therefore, I thought this factor should be the emission of coal mining activity.

Information of the coal mining

Responding to first answer, I investigated the coal mining activity in this area. Here is an figure of one of the coal strip mine and the coal is mined by mechanical cutting techniques.

enter image description here

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    $\begingroup$ For clarification of the plots: 'fraction' is the ratio (element X in PM2.5)/(element X in PM10)? $\endgroup$ – daniel.neumann Jan 23 '18 at 14:50
  • $\begingroup$ What is the location? $\endgroup$ – farrenthorpe Jan 23 '18 at 15:45
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    $\begingroup$ @daniel.neumann, the fraction of a certain species means the relative loading of the species in this factor. $\endgroup$ – Han Zhengzu Jan 24 '18 at 2:33
  • $\begingroup$ @farrenthorpe, the sampling campaign is conducted in China (location 42N, 119E). I have added one figure to depict the location of the site near the coal mine $\endgroup$ – Han Zhengzu Jan 24 '18 at 2:36
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    $\begingroup$ I think you might also consider the influence of resuspension, depending on the age of the mine. Their may be settled metals in the surrounding region that get resuspended due to agricultural activity, vehicles on roadways, or high wind events. $\endgroup$ – farrenthorpe Jan 24 '18 at 6:04

The first thing to consider is, if it is not the adjacent coal mine, what other nearby sources could produce such a result. Is there a coal fired power station or a factory nearby. If there are no other likely sources then the coal mine is still the most likely candidate as the source of the dust and metal contaminants.

The other thing to consider is how is the coal being mined in the open pit and how is dust being generated by the coal mine.

The most likely method of mining the coal would require the use of explosives and blasting. This can create large clouds of dust that can be high and wide. If the wind was not blowing when a blast occurred the dust may have reached your sensors.

If the coal is mined by mechanical cutting techniques dust will still be generated, but not in the same quantities as blasting produces.

The other ways dust is generated is by vehicles travelling on unsealed roads - the tyres of the vehicle churn up the dust on the roads.

Dust can also be blown from trucks loaded with coal or from conveyor belts conveying coal to a dump site. The loading of trucks will also generate dust, as will the dumping of coal.

From experience, the only way to control dust is to constantly spray with water. Do you know if the mine uses any for of dust suppression?

It is well known that coal contains all types of contaminants, including metals such as cadmium and mercury. Different deposits have different types and degrees of contaminants.

From what you have presented, the coal mine is the most likely source of the dust and metal contamination.

  • $\begingroup$ Thanks for your valuable answer. I have added more information in the question to respond your question. $\endgroup$ – Han Zhengzu Jan 24 '18 at 2:42

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