@Swagata

In the reference you give the size distribution starts at 0.2 micrometer. This is due to the (optical) instrument used that has its lower limit at this value

For smaller particles an SMPS is used and in general the number of particles smaller than 0.2 micrometer is much larger than the number larger than this value.

However the small particles do not represent significant mass:

1000 particles of 50 nm carry only 10% of the mass of ONE particle of 1 micrometer

It is hard to get size distribution from a single measurement like PM2.5, which can only represent an integrated information for the measured time period. As I know of, the AOS system that can measure the aerosol distribution, which may have certain relationship to the PM2.5 measurement.

Mr. Xiquan Dong. Thanks so much!!

Best regards from Colombia!!

Yes. This is possible with some simplifications. Two most important simplifications are (1) Particle is treated as sphere then you can compute volume by 4/3 * (pi)* (radius) power 3.

(2) The constant density (rho).

So volume multiplied density will give mass. After that you need to use any available algorithm. If you have still problem, can contact me again.

All the best.

@Swagata

Well you give us the reference then. In general the size DISTRIBUTION has no relation with TOTAL mass because the mass is dominated by a few large particles

@ Xiquan

What is AOS?

@Harry. You are right that "mass is dominated by a few large particles". But still few assumptions are available. I had a short communication before but the most cited one is Cheng, Y. H., & Lin, Y. L. (2010). Measurement of particle mass concentrations and size distributions in an underground station. Aerosol Air Qual. Res, 10, 22-29.

@Swagata. Figure 2 of the cited reference illustrates Harry's point of view. Size distribution is presented against mass concentration, where upper and lower limits of the error bars are single (!) s.d.'s. Variability is large then. The authors used a Grimm 1108 based on opticle principles and capable to deliver mass levels and size distributions. The algorithms used to convert particle counts and mass levels are known but to the manufacturer. PM levels should always be calibrated against a reference method at each monitoring site, and size distributions alike compared with for instance a SMPS.

Thanks for your comments @Marcel. I agree on that. I knew that method is not perfect but still it gives an idea.

Good discussion is going on and it is great.

@Swagata

In the reference you give the size distribution starts at 0.2 micrometer. This is due to the (optical) instrument used that has its lower limit at this value

For smaller particles an SMPS is used and in general the number of particles smaller than 0.2 micrometer is much larger than the number larger than this value.

However the small particles do not represent significant mass:

1000 particles of 50 nm carry only 10% of the mass of ONE particle of 1 micrometer

Harry is absolutely correct.  It is possible to have a very large nucleation mode that dominates particle number and greatly impacts size distribution and yet would not show up in optical measurements and would not dominate particle mass in a PM2.5 mass measurement.  There just isn't a one-size-fits-all conversion that is at all reasonable since there are just too many variables. In addition to the SMPS and other similar size/number measurements based on electrical mobility, there are also diffusion-based measurement methods that can effectively characterize sub-micron size distributions (e.g., parallel flow diffusion battery, DISC-mini, etc.).