Dear Sidra, first it is important to define OC. From my point of (soot expert), soot particles could be define in several part of carbon species; OC (organic carbon, mostly HAP, COV, hydrocarbons...), EC (elemental carbon, mainly amorphous or gaphitized carbon) and carbonate carbon (CC). You can find more detail in Petzold et al. (Recommendations for reporting “black carbon” measurements, Atmospheric chemistry nd physics, 13, 8365-8379, 2013). For the OC fraction this part could be produced during combustion or ageing of other aerosol and gases in the atmosphere during their transport. In most case weathering of combustion generated particles will tend to increase the content of OC at their surface by adsorption or condensation. This is only my point of view for soot particles and trying to resume the reaction of OC with these particles is not an easy task to do. I will recommend reading of Ning and Sioutas (Aerosol and Air Quality Research, 10: 43-58, 2010), Braun (Geophysical research letters, 36, 2009) and many others...

Ken

Sorry to correct you but the term "soot" is a popular description for aerosol containing a large proportion of non-OrganicCarbon, that is: soot contains a large fraction of Elemental Carbon. This is inert.

General answer:

OC is a bulk term for thousands of organic compounds that have in common that they have a low vapor pressure so have a relatively large molecular weight and/or contain polar groups.

Then there is the distinction in primary and secondary OC: primary OC is emitted at a source; secondary OC is made in the atmosphere from gaseous emissions. The Secondary OC is the result of a reaction sequence and often an end-product.

An example of a reaction of an OC compound is that of oxidation of benzpyrene and ozone

Another is the polymerization of glyoxal, itself an intermediate gaseous product in the atmospheric oxidation of for instance toluene and terpenes.

And to answer your question very directly:

There are hardly pure OC particles. The OC is mostly internally mixed with inorganic compounds, especially sulphate. This means one atmospheric particle contains several compounds. Sulphate will not react with OC because it is also the end-product of an atmospheric oxidation process.

OC can also be in particles together with nitrate. Also nitrate is not a chemically active compound. It also is the end-product of an atmospheric reaction path.

In addition. OC can also be plant debris and this OC is in a pure particle of a large size. It will not significantly contact other particles during its short residence time in the atmosphere.

Summarizing, OC  is a very complex "compound" and its chemical are as diverse as its detailed composition, which is most of the time only very poorly known.

I like to refer to review articles on OC by the real experts in the field, such as prof. Barbara Turpin and the late Glenn Cass. Here is also a short description of OC:

http://www.ipcc.ch/publications_and_data/ar4/wg1/en/ch2s2-4-4-2.html

Ken

I like to comment on your comment

Soot as emitted at sources is composed of A large fraction of elemental carbon

THE problem with the analysis of carbon in aerosol is that thee is not a basic definition of elemental carbon.

Elemental Carbon is now defined by the analysis method of which several exist. However, the proportion of EC in primary emitted soot is from 40-70% as measured with the best accepted methods. This is for the most important soot of the "developed" countries: diesel smoke.

As for the radiative forcing effect:

All aerosol components scatter light. elemental carbon is the most important component that absorbs light and thereby is a true greenhouse component. To complicate the issue:

Elemental Carbon embedded in other material absorbs more light because of a lensing effect.

The other compounds come onto the aerosol by condensation and reaction of gaseous compounds like the earlier mentioned sulphate and nitrate. Elemental Carbon is in sub-micron aerosol particles. t is therefore not associated with seasalt and also not with mineral dust and not with plant debris material

Ken

First of all: I was in coal combustion for quite some time and thus familiar with that kind of carbon also but mostly working with bituminous coal as used in the power stations in the Netherlands

1. Yes natural elemental carbon is present in the  forms you mention (not my field of expertise)

2. Plants are organic carbon almost by definition; also peat 

bituminous coal consist of a majority of OC: when pyrolised a minority is coal-char.

3. In the atmosphere the elemental carbon is partly graphite like as determined with Raman-spectroscopy'; also the diffraction pattern of diesel soot shows graphite-like nano-domains in the rounded primary particles. I refer to proof Friedlander's work as well as Sarofim.

4 as mentioned soot acts as the nucleus for other secondary material to condense on or to be formed upon. This starts at the exhaust where (part of) the OC components condense on the primary soot particles. Sulphate and nitrate are formed in the atmosphere. Sulphuric acid mostly condense as a vapor onto existing particles. Nitrate forms aerosol-material at the surface of soot in the form of ammonium nitrate.

T

Ken

The question is literally on OC, I cite:

"How does Organic Carbon (OC) react with other atmospheric particles"

And the atmospheric aerosol community differentiates carbon in aerosol in OC and EC, where EC corresponds with the light absorbing carbon, better known as Black Carbon.

It depends on the substance you consider, because OC meaurement  in particulate matter is related to hundreds of organic compounds and only a part of them has been identified so far  (every monitoring site can have a different OC composition, too) .

If you want to prevent your aerosol samples from changes in OC composition,  transport and storage them at low temperature . The European Committee for Standardization recommends a temperature below 5°c