Dear all,
I am struggling to calculate the specie specific uncertainty for Polycyclic Aromatic Hydrocarbons in Positive Matrix Factorization version 5. I was reading the guide however, could not understand how to calculate uncertainty. Below is the paragraph given in PMF guide.
"The equation-based uncertainty file provides species-specific parameters that EPA PMF 5.0 uses to calculate uncertainties for each sample. This file should have one delimited row of species, with species names (Table). The next row should be species-specific method detection limit (MDL) followed by the row of uncertainty (species-specific). Zeroes and negatives are not permitted for either the detection limit or the percent uncertainty. If the concentration is less than or equal to the MDL provided, the uncertainty (Unc) is calculated using a fixed fraction of the MDL "
Table
Unc. Aluminium Ammonium Arsenic Barium
2 0.00419 0.0125 0.00098 0.0068
10 10 10 10 10
In above mentioned Table decimal values are MDL value of given species but I don't know that what is "10" and "2", if 10 is uncertainty then how can we calculate it?
Secondly I have 52 weeks samples (1 sample per week and 17 studied species). My question is whether I have to calculate Uncertainty of all species for all sample or I can use only one uncertainty values for all samples.
Hi Waqar,
The uncertainties for each PAH species should be determined as part of your analytical method. Presumably you have quantified your PAHs using some GC/MS variant so there will be plenty of literature out there about how different groups have calculated uncertainty. The USEPA would also likely have a guide for quantifying uncertainty for the analysis of PAHs because there is a standard method. Your analytical method should also produce MDLs which can be used to calculate uncertainties for those samples below the MDL. I would highly recommend reading:
Polissar, A.V., Hopke, P.K., Paatero, P., Malm, W.C., Sisler, J.F., 1998. Atmospheric aerosol over Alaska: 2. Elemental composition and sources. Journal of Geophysical Research: Atmospheres (1984–2012) 103, 19045–19057 and Kara, M., Hopke, P.K., Dumanoglu, Y., Altiok, H., Elbir, T., Odabasi, M., Bayram, A., 2015. Characterization of PM Using Multiple Site Data in a Heavily Industrialized Region of Turkey. Aerosol and Air Quality Research 15, 11–27. doi:10.4209/aaqr.2014.02.0039
which should give you an idea how to treat your data. To answer your other question, depending on how your uncertainty is calculated, you may have one value for each PAH, or you may have a different value for each PAH in each sample.
A few things appear a bit problematic with your wider study. First, 52 samples is quite low for a source apportionment study. Typically you would want more than 100 samples. Obviously sampling for longer may not be possible all the time, but the small number of samples could cause problems. More concerning for me is your attempt to apportion PAHs. I know in the literature this is widely reported, but care should be taken before you embark on this. I recommend reading:
Galarneau, E. 2008. Review: source specificity and atmospheric processing of airborne PAHs: implications for source apportionment. Atmospheric Environment, 42: 8139-8149.
This paper highlights a number of problems with trying to apportion PAHs, most notable of which is that PAHs do not satisfy the most basic "rules" of receptor modelling. The arguments against trying to apportion PAHs are well-presented in the paper and may convince you to try using your data another way.
I hope this information helps and good luck with your work.
Travis
Dear Waqar,
I have the same question would you please help me in this regards.
Dear Travis,
I have read the mentioned article, but since my major doesn't related to the this field I couldn't figure it out
I look forward to hearing from you
best regards
Kirash
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