Hello Chin,

With ICP-MS and depending the sensibility of your analysis I could think:

-Analysis material, which compounds are made? Could be any contamination? (Think that a typical alloy for steel are Fe-Mn for do it very strong...) 

-Pollution nearby industry, building materials, dust...

-About dust, which kind of ground are in all region, clays, granite, sand...

Other question could be, other elements that you didn't find, why not?

Problem could be very extensive, but first think to do, should make ALL question, from absurd one to the more complex.

I hope it helps you to find the answer, but it could be a very complex study.

The dust and smoke around that region may have been contaminated with those metals which are then washed down by the rain. It is important to note that air pollution is dynamic. The dust or smoke mentioned may have originated from other place.

Find an attached article which could give some help. 

Thanks

Article POTABILITY OF HARVESTED RAIN WATER IN SOME LOCAL GOVERNMENT ...

Dear Chin

Prolong drought and haze episode might be said as event or phenomena seem together with monsoon or issue e.g El Nino and La Nina. Those studies on sources of trace metal only a common and should look into main transporter i.e wind, chemical weathering  and rain. looking into your area you shall consider on wind trajectories either from northeast or southwest.  Hopes this will help for you guideline.

Best regard's

Zolhizir Bin daud

Dear Chin,

 The sources of Al, Mn and Fe from the crustal materials like dusts and less influenced by anthropogenic sources in the rain water. However, K should be most likely from the biomass burning. Also, you can refer a recent article " Concentration of trace elements in wet deposition over the central Himalayas, Nepal". 

Best 

Lekhendra Tripathee

Dear Chin

Rain water is basically runoff water ,carrying contamination from non point sources. So you may need an environmental base line study of the study area. After that you can able to findout the answer of your question.

Best regard

Aziz ur Rahman 

a first question is what are these compounds present in normal rain too? and if how much higher are their concentrations in this episode? why do you want to know the origin?

And in addition we need answers to the information required by Joaquim before anyone can help you

Dear passionate researchers,

Thank you for your questions and answers, and most importantly your efforts in trying to help. 

The analysis was carried out using clean labwares and high quality chemicals. Therefore, contamination derived from the lab or during handling process could be very minimal.

The duration of dry spell before the 1st rain I collected is approx. 4 months! The study area is situated in a valley (know as Klang valley). Nearby the study area, there is a small patch of forest reserve area (at the eastern side). The sampling location is situated at the National University of Malaysia. Approx. 10 km away from the University is Kuala Lumpur city where heavy traffic occurs most of the time (at the Northern side). 20 km south is where KL International airport locates. 50 westward from the study area is the Port Klang and straits of Malacca. There are heavy industrial area located in between Port Klang and the study area (25km away). 

In terms of its geology, wide range of rocks such as limestone, sandstones, silt, sands, clays, phyllite, schists, granites can be found in the vicinity. Most of the forested area in the valley has been given way to construction.

I analysed other major and trace metals as well. It just happens that I found difficulty in explaining the pattern of these metals. The pattern of K is quite different from those of Na, Ca and Mg.

I strongly agree with Dr. Zolhizir to consider the wind trajectory. I will work on HYSPLIT at the later stage of this research. But presently, I am curious about the possible sources of Al, Mn, K and Fe in the rainwater. 

I am quite convinced by Dr. Lekhendra who stated that K could be likely derived from biomass burning in view of its slightly different trend with Mg, Na, Ca. 

Answering Dr. Harry's concern, the compounds are inorganics I suppose. The water samples were filtered (0.45um), acidified and analysed using ICP-MS. These metals did not showed significantly higher concentration during the 1st rain. Their concentration generally drops further during the 2nd and 3rd rain before it rises again in the 4th, 5th rain. The trend appears much more erratic after the the 6th rain but still stays within an acceptable range. I need to get an idea on the possible origin and a clearer view of these metals in the rain or possibly its fluxes in our atmosphere.

Thank you very much. I hope I've answered all your question so far. Please let me know if you have other queries.

Sincerely,

Chin Yik Lin

Dear Chin,

A few thoughts:

- I agree that in general water soluble K is a good indicator of biomass burning in both precipitation and ambient particulate matter.

- Crustal contributions (wind blown dust) can be a dominant contributor in arid locations.  It is interesting that you filtered the samples prior to acidifying them since crustal elements typically have relatively low solubility.  You also did not indicate how aggressively you extracted the samples (e.g., types and concentration of acids, microwave extraction).  I would also expect to see some lanthanide elements if crustal sources are significant.

- iron/steel production, coal combustion, oil combustion, and incineration are also significant sources.

- iron/steel production is generally a significant source of Fe, Mg, V, Cr, Mn.  Interestingly, lime is used as a fluxing agent in blast furnace operations so Ca emissions are also significant (especially if they do slag/sintering operations on site).

- if you have a large number of samples 80+ you could use source apportionment/receptor modeling tools to elucidate the sources (e.g., Positive Matrix Factorization, Unmix).

 http://www.epa.gov/heasd/research/pmf.html

http://www.epa.gov/heasd/research/unmix.html

- Investigating ambient particulate matter in arid areas can also provide insight into the chemistry of wet deposition.

A few resources if you are interested ...

Keeler, G.J.; Landis, M.S.; Norris, G.A.; Christianson, E.M.; Dvonch, J.T. (2006). Sources of mercury wet deposition in eastern Ohio, USA. Environ. Sci. Technol. 40, 5874-5881.

White, E.M.; Keeler, G.J.; Landis, M.S. (2009) Spatial Variability of Mercury Wet Deposition in Eastern Ohio: Summertime Meteorological Case Study Analysis of Local Source Influences. Environ. Sci. Technol. 43, 4946-4953.

Graney, J.R.; Landis, M.S. (2013). Coupling Meteorology, Metal Concentrations, and Pb Isotopes for Source Attribution in Archived Precipitation Samples. Sci Total Environ. 448, 141-150.

White, E.M.; Keeler, G.J.; Barres, J.; Landis, M.S. (2013). Determination of Mercury Wet Deposition Physicochemistry in the Ohio River Valley through Automated Sequential Sampling. Sci Total Environ. 448, 107-119.

Vedantham, R.; Landis, M.S.; Olson, D.; Pancras, J.P. (2014). Source identification of PM2.5 in Steubenville, Ohio using a hybrid method for highly time resolved data. Environ. Sci. Technol. 48, 1718-1726.

Pancras, J.P.; Landis, M.S.; Norris, G.A., Dvonch, J.T. (2013). Source apportionment of ambient fine particulate matter in Detroit, Michigan, using hourly resolved PM chemical composition data. Sci Total Environ. 448, 2-13.

Best Regards,

Matt

Little difference in composition for the rain events

This means that the extended period of haze/dryness did not affect the composition; so why did you mention then the dry period? It seems thus that the metals you measure are not very sensitive to the situation outside the rain.

Why do you filter the sample? Al, Fe and Mn are present in aerosol-particles that are larger than 2.5 micrometer, in most regions of the world. I think there must also be data for your area

Dear Matt,

Thank you very much for your interesting comments and the useful references. I will read through the manuscript given. Appreciated.

Dear Harry,

Marked difference (or scavenging effects) can be clearly seen in some other elements but not the metals discussed here. 

I aimed to study the soluble/dissolved metals in the rainwater, this is the reason why I filter the samples. Another set of unfiltered rainwater samples has been subjected to strong acid digestion on ~100 centigrade hot plate. But, I did not look into the results yet. Unfortunately, I did not considered particulate matters at this moment. I only focus on the dissolved metals in rainwater. PM has been collected by other members from our group.

Regards,

Chin Yik Lin

The components in the rainwater are from the particulate matter. This particulate matter consists of particles that are taken up in the rain(droplets). Also, water condenses on the particles in the clouds and these cloud droplets grow to rain droplets.

What you measure is thus the fraction of the elements that dissolves in the water.

Another question is your rain collector an open collector or a "wet only"?

In the case of en open collector there can be dry deposition of the large particles that contain the mentioned elements and then the rain comes into it too

The elements you are questioning are most likely solubilized into the wet deposition from suspended (sindblown) soil.  Several references that I know of refer to this (they are a bit old, but still useful and have wet precip conc for these elements).Scudlark et al 1994 Atmos Env; Scudlark et al 2005 Water Soil Air Pol; Conko et al Atmos Env 2004 and Kim et al Atmos Env 2000.   If you do not have access to these send me personal message and I can send you pdf.  cheers! 

Kathryn

Mn is an element that is emitted in iron/steel production in combination thus with Fe; google for "EPA manganese iron sources PM2.5". Mn is also used in additives for gasoline but what do we know about the sources in the country of the questioner that  is the first thing a scientist should seek out for himself

I was speaking generally, and stand corrected, of course there are other sources each of these elements and the researcher should identify these in his or her own situation. however, this is one very common source and one that is often overlooked when seeking more anthropogenic sources.

@ Kathryn

My apologies to you

My strong words were towards the questioner who must do his normal job on searching for where these elements can come from before asking the field

And actually in ResearchGate his question should specific and dot a generic one as he does now

Dear respected Professors,

I sincerely apologize to all of you for asking a generic question such as this. However, I've learned a lot of great information through your helpful discussions and advice here. It has remarkably narrow down my scope in searching for possible sources since I am still very new in this field.

On top of this, I've run a statistical test (Cluster Analysis). Here, I would like to share with you the groupings by variables (given in the attachment). 

Again, I am sorry and thank you very much for your time and contribution.

Regards,

Chin Yik

Dear Chin

I admire your latest response! You are a rare example of a questioner who is very rapid in answering and even apologizing! 

Dear Chin,

I agree with Dr. ten Brink. Please, keep your attitude!

I looked at your CA dendrogram and it shows an unusual grouping. How many samples did you analyze? The elements you are studying must be associated to particulate matter in the atmosphere.

Usually, Na, Mg, Al, Si, Ca, Ti, Mn, Fe and Zr are produced by geological material (soil), which can be blown by the wind or resuspended from streets by cars, for example. Moreover, a fraction of K also comes from soil, but there is also an important contribution by smoke (forest fires, for instance). Smoke particles also contain some S and Cl, so the group with K-Cl looks reasonable. If you are close to the sea, you would also expect some marine aerosols, which contain Na, Cl and K. So, that group might also have a marine contribution.

As explained above by other contributors, some times Mn and Fe also may be produced by industry, and as they appear correlated to Cu and Zn in your dendrogram, this should be the most important source in your samples. Fe has also been associated to car brakes (with other elements, like Cu, Zn and Sb).

Cr and Ni could also come from an industry. Finally, I cannot explain why SO4, NO3 and Al appear in a single group.

Although they are rather old, you may read a few papers we published about elements in aerosols. Of course, there are more complete references in the subject.

Article Elemental Analysis of Soils as Possible Resuspended Dust Sou...

Article Absolute principal component analysis of atmospheric aerosol...

Thank you very much Dr. ten Brink and Dr. Javier. Your information have been very clear and useful. For your information, I only consider 14 samples. Just out of curiosity, could the SO4, NO3 and Al group belongs to motor vehicle/industrial contribution?

Thank you!

SO4 and NO3 are not directly emitted but are formed in  the atmosphere from

SO2-gas and NOx-gas. SO2 is typically emitted by power stations (without filters for the compound)

NO2 is emitted by power plants and traffic (as well as households and industry)

NO3 and SO4 are made in the atmosphere thus not a local type of aerosol and thus often transported over often hundreds of kms; but this fully depends on the location of the dominant sources of SO2 and NOx in your region

Al is in general part of soil dust thus it is curious to see such a correlation with the two mentioned compounds. But again it might be that the sources for all 3 compounds is in the same area. However Al is typically blown up under dry and windy conditions

 14 days is a rather small number for a correlation matrix

Thank you for the information Dr. ten Brink. I shall look into the wind trajectory to see if there is other possible sources that could help explain this.