(adsbygoogle = window.adsbygoogle || []).push({}); 1. The problem statement, all variables and given/known data

We have to calculate the mass concentration for a particle size distribution. I'm just doing the first size range here, since once I get that the rest is just repetition.

FYI, the particles are spherical.

Size range (diameter) = 0.005-0.5 μm

Average particle size (diameter) = 0.25 μm

Number concentration = 1 cm[itex]^{-3}[/itex]

Particle density = 1800 kg m[itex]^{-3}[/itex]

The answer is supposed to be in units μg m[itex]^{-3}[/itex] μm[itex]^{-1}[/itex]

2. Relevant equations

[itex]m=\rho _{p}\frac{\pi }{6}D_{p}^{3}n_{n}(D_{p})[/itex]

3. The attempt at a solution

First thing I did was convert the density from kg m[itex]^{-3}[/itex] to μg m[itex]^{-3}[/itex]:

[itex]\frac{1800 \: kg}{m^{3}} * \frac{1\: \mu g}{1*10^{9\: }kg}=\frac{1.8*10^{12}\: \mu g}{m^{3}}[/itex]

Then I plugged into the mass concentration formula:

[itex](1.8*10^{12}\mu g\: m^{-3})(\frac{\pi }{6})(0.25\: \mu m)^{3}(1\: cm^{-3})=1.473*10^{10}\mu g\: m^{-3\: }\mu m^{3}\: cm^{-3}[/itex]

So now, since there's no cm in the units we're supposed to have, I figured I'd get rid of that:

[itex](1.473*10^{10}\: \frac{\mu g\: \mu m^{3}}{m^{3}\: cm^{3}})*(\frac{100\: cm}{1\: m})^{3}=1.473*10^{16}\: \frac{\mu g\: \mu m^{3}}{m^{6}}[/itex]

So now we have this mess, and at this point I give up, because idk how the heck to get this in μg m[itex]^{-3}[/itex] μm[itex]^{-1}[/itex]... Not to mention the number I'm getting seems way too large...

**Physics Forums | Science Articles, Homework Help, Discussion**

The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

# Homework Help: Unit problem with calculating the mass concentration of a particle

Can you offer guidance or do you also need help?

Draft saved
Draft deleted

**Physics Forums | Science Articles, Homework Help, Discussion**