I must say inorganic aerosols are predominantly secondary even though there is no general rule for that. Scientists say secondary pollutants ( aerosols) are those that are indirectly released into the atmosphere, that is, those which are formed from primary pollutants in the atmosphere. Even though they can be discharged directly into the atmosphere, it is usually not the case. A gas like N2O is known to occur naturally. About 80% of it is naturally produced. This gas is converted to NO and NO2 when released into the atmosphere after a series of reactions with oxygen. NO and NO2 can therefore be regarded as secondary. However, this does not mean they cannot be primarily emitted. Factories which deal in the manufacture of gases artificially are likely to release some of these gases directly into the atmosphere. Its the same with SO4, NO3, NH4, CO,etc. Take CO for instance. It is the most released aerosol in our environment. And it is released directly. However, one cannot generalise the fact that inorganic aerosols are predominantly primary because only CO is releasd directly into the atmosphere. Generalisation has to be made by taking everything into consideration, and if one takes all the gases into consideration, i think the conclusion must be that inorganic aerosols are predominantly secondary

Ions, such as SO4--, NO3- etc., may either be primarily emitted, or indirectly released due to secondary formation, so I don't think it's safe to make any kind of generalization. What you need to do (in my opinion) is to apply a Source Apportionment (SA) method to your dataset, such as Chemical Mass Balance (CMB), or Positive Matrix Factorization (PMF), in order to discriminate between primary and secondary formation.

I agree with Georgios, but I am not sure that PMF is able to discriminate from primary and secondary origin of ions like SO4, NO3, NH4 ...

Full modelling of the reactions may even point out that even if several of the precursor emissions go down, more secondary PM may still be formed. 

Article The Effect of Changing Background Emissions on External Cost...

Generalisation is: they are virtually completely secondary

Read the textbook by Seinfeld&Pandis and do not consult a blog like this one where you get wrong answers

In english it's amusing to say they these aerosols are primarily secondary, which they are.  As GA notes, they can come from primary source - nitrates, e.g. can be found in the coarse mode, in part from soils, in part from nitric acid that preferentially attaches to more basic coarse particles over fine acidic sulfate droplets.   So called 'primary' sulfate emissions can be a mixed category - SO3 emissions (which are essentially anhydrous sulfuric acid) can form rapidly near sources and could be indistinguishable from primary sulfate, although they undergo atmospheric transformation.

I am somewhat confused by aspects of DA's comment.  CO (carbon monoxide) is not an aerosol, but a gas - it produces secondary products like ozone and CO2, but it's not a particle.  Perhaps he is referring to OC, i.e. organic carbon, which is definitely emitted as primary particles from incomplete combustion along with BC (black carbon) - but up to 40% or more of ambient OC can be secondary particles in some conditions e.g. summertime with biogenic and anthropogenic VOC emissions.  

John:

Agreed SO3 is directly emitted but it is most often only a fraction of the SO2. For coal combustion it is equivalent to an average one hour oxidation of SO2 in the plume and the reason that many models do not even consider the primary emission

Than the nitric acid gas: that is also a secondary product from NOx emissions or do you I miss a primary source. Similarly NH4 from ammonia

greetings Harry

The only correct statement is that major contribution of these ions is from secondary formation.

In my opinion sulphate, nitrate and ammonium ions in the fine fraction particulate matter are the major precursor of secondary aerosols which is transport long distance. But the ions in the coarse fraction of particulate matter can be reflect the secondary aerosols and primary source that can occur in the particulate matter from the combustion activity near the location.  

With respect to your comments particularly about sulfate, another important source is sea salt, in which the concentration of this ion is usually around 10%, according to the SPECIATE database (Profile Number: 4310110). It is also well known that this ion is already present in seawater, due to the oxidation of Dimethyl Sulfide (DMS) emitted by phytoplankton, so it is definitely emitted as a primary aerosol, in this case.

Ulku

the precursors of the secondary ionic components are the gases NOx SO2 and NH3

the secondary components are the products of the reactions

Georgios

indeed seasalt contains sulphate but mostly in the form of coarse particles and associated with NaCl and more specifically magnesium;

A few emission inventories estimate the amounts of inorganic ions that are emitted in particulate form (i.e., primary).  For example, Reff et al. (Environ. Sci. Technol. 2009, 43, 5790–5796)  tabulated the quantities of each ion that are emitted as primary PM2.5 from the U.S. during 2001.  Figure 2 of that paper shows the various sources that emit each of those ions.  From a careful study of the Supporting Information for that paper, it is possible to compute the numerical amounts depicted in Figure 2.

Yes NO3- , NH4+ and SO42- are secondary ionic components. And, they can be identified in aerosol after the conversion processus of gases to particules.

While, sea salt aerosols can be a source of sulfate but in urban area (and without mentionned that can be coast area) we can consider that 100% of sulfate is orginate of anthropogenic activity and it's considred as secondary pollutants. 

Yes, they are predominantly secondary inorganic aerosols.