Thanks Marc.

to Marc Mallet

Sorry

In radiation forcing the particles that are most efficient in up-scattering of solar radiation are of concern. On a mass basis especially particles with a diameter that is close to the wavelength of the solar light thus 0.3 to 1.5 micrometer are of interest. The reason is that smaller particles scatter much less light by rayleigh scattering that goes according to d^-6. Mass goes with d^3 so on a mass basis the scattering goes as d^-3.

Larger particles scatter light according to their projected area (Mie / geometrical scattering) but on a mass basis this than goes according to d^-6

With typical particle mass distributions this means that the peak scattering is 0.3 to 1.5 um

See for instance: Friedlander Smoke dust and haze

Chapter 5

NB: it does not take into account the up-scatter fraction

In cloud physics the particle number is the key factor; thus not

PM1. Actually the threshold for activation is around a few tenths of a micrometer depending on cloud type and particle total number

To Marc

I agree with your mentioning coarse particles. Fact is that for radiative forcing in my art of the world these play a negligible role.

When they are present it is in the form of Sahara dust. This is natural and the occurrence is rare.

On the other hand: the role of nitrate was not acknowledged for some time because where the forcing was studied nitrate was present in rather coarse particles. We found it has a mass distribution similar to that of sulphate and even more peaked in the most efficient size range of around 0.5 um

Finally, I am working on a manuscript in which it is seen that the nitrate is thereby in particles that are much less efficient as cloud nuclei

And lastly the role of nitrate in visibility reduction was already known for the LA area in the 1970s, but it took us/me until the early 1990s to see the similarity of "our" aerosol with that in SoCal. There is a difference though because nitrate in our region is important also in summer while in the LA-region its concentration is low, because it is in the gas-phase.

Dear Vishnu,

Please note the scientists found out some different behaviors (Mineralogically, Geochemically, Health exposure, etc) on particles happen since they are in different sizes. So, those numbers have a nature and severe works on them have told us about that.

Kind Regards.

Hesam/

I think that it was nicely explained before about the modal distribution of aerosols and how it is also related with radiative properties, cloud condensation nuclei, etc. In principle, from a climate-aerosol model perspective once you have the aerosols modelled you may calculate whatever you consider useful for your studies: PM10, PM2.5, PM1, PM20 or any other. Just consider that PM10 are particles with diameters up to 10 micrometers (so it will be similar to PM9 or PM11, in values and also from the point of view of physical processes involved). PM2.5 are particles up to 2.5 micrometers.

From the experimental point of view, many instruments has been build to measure in specific size ranges, and PM10 and PM2.5 are two main set up to estimate surface concentrations. Still, the presence of large particles (dust, sea salt for example) with diameters of 20 micrometers or larger are an active research area.

From the point of view of air quality (rather than climate modelling) it is important to differentiate sizes when they are related with anthropogenic vs natural sources. Here PM10 threshold is important as it is the threshold in which they are going into the lungs and can produce health issues, so a reason to measure this range of particles in the atmosphere.

PM i a parameter for Air Quality

I strongly advice you to google for

EPA respirable and inhalable PM