Define you term and explain the problem.

There are several processes that produce aerosols. Whether the process is primary or secondary depends on conditions producing the aerosol and often the size of the aerosol. The measurement of aerosols in a given size range depends on where one is temporally in the process.

Why should you care about the process of producing the aerosol at the time of measurement?

Yes. There are many studies that investigated the temporal changes in aerosols and reactive species after release from a source. Knowing the possible history of development can help in identifying the source. 

Classifying as primary or secondary has little meaning for a given sample of aerosol. The process and purpose of the sample might be a reason for classifying aerosols.

We can distinguish between primary and secondary aerosols by identifying their chemical composition. Based on Pöschl (2005), page 7527

http://www.met.tamu.edu/class/atmo689-gs/lectureweek10/aerosolreview.pdf

the method is based "on identification and quantification of organic compounds" in the aerosol particles. The list of the specific techniques is quite impressive and it includes the standard analytical methods, liquid and gas chromatography as well as mass spectroscopy.

The paper contains a complete list of the references to the specific methods and the wealth of information about the atmospheric aerosols in general.

Dear Tabish and Janusz

Primary particles are directly emitted by processes such as biomass burning, incomplete combustion of fossil fuels, volcanic eruptions, and wind-driven or traffic-related suspension of road, soil, and mineral dust, sea salt. Also biological aerosols are important  and often ognored (plant fragments, microorganisms, pollen, etc.) and considered as primary aerosols. Secondary aerosols  are formed by gas-to-particle conversion in the atmosphere (new particle formation by nucleation and condensation of gaseous precursors). You can also have a mixture of both as biological micro-organisms can stick on SOA (mixture of primary and secondary aerosols). One kind of  hybrid is called polluen (pollutant + pollen) (see http://www.jle.com/fr/revues/ers/e-docs/synergie_entre_pollens_et_polluants_chimiques_de_l_air_les_risques_croises_130005/article.phtml). This mixture is rarely considered.

Concerning oxidized nitrogen only NO (nitrogen monoxide) and N20 (nitrous oxide) are directly emitted in the atmosphere. Particles of NO3-  is formed through reactions in the atmosphere and is therefore a secondary aerosol.

Concerning reduced nitrogen, only NH3 is produced and NH4+ is obtained through oxidation and therefore is a secondary aerosol also. Same for sulfates.

Sulfate, nitrate, and ammonium are important inorganic constituents of urban aerosol particle and account for 30-70% of PM2.5. Through filter packs , it is  possible to identify these species. However, there are numerous challenges ( see

Ref: https://link.springer.com/article/10.1007/s11430-014-4986-)

In fact, accurate determination of the chemical composition of air particulate matter is a formidable analytical task.  (see Poesch p 7523 near the bottom, i.e. refered by Janusz above )

So the bottom line is a knowledge of which species is primary and which is secondary is helpful but not sufficient given the complexity of the problem (contamination by biological particles, formation of hybrid, etc.). Actual technique cannot resolve everything.

My hope in the future is that a particularly challenging application of aerosol mass spectrometry develops, i.e. the one with high relevance for public health and security is the identification of biological particles and pathogens (bacteria, viruses, spores, etc.). i.e primary and secondary mixed aerosols.

Hope it helps

Alain

NH4 is not an oxidation product but an acid-base product from a reaction of ammonia with sulphuric acid / nitric acid / oxalic acid

Right  Harry!

I apologize for the mistake here. Should read acidification not oxidation.

Thanks for pointing this out

Hi Tebish,

We attempted to distinguish primary and secondary aerosol based on chemical analysis of filter-based samples (PM2.5) collected over a period of one year.

http://www.sciencedirect.com/science/article/pii/S1352231015301515

I hope this article may help you.

Neeraj

using radiunoclides , you can detect deposition and re-suspention of particles usind Pb-210, K-40,