Question

The peak concentration of organic aldehydes on a smoggy day reaches 0.5 ppm. If the aldehydes condense into organic aerosol with average particle diameters of 1 um and average densities of 1 g/cm3, estimate the aerosol particle concentrations resulting from the aldehydes

Answer 1

1 ppm = 1 mg/L

So, peak concentration of organic aldehydes = 0.5 mg/L

                                                                     = (0.5*10^-3 g)/(1000 cm³)

                                                                     = 5*10^-7 g/cm3

Given, average particle diameter = 1 μm

Average particle radius = (1/2) μm

= 0.5 μm

= 0.5*10^-4 cm   (1 μm = 10^-4 cm)

Average particle volume = (4/3)*π* (0.5*10^-4) cm³

                                                                = 5.235*10^-13 cm³

Average particle mass = Average particle volume * density

                                      = 5.235*10^-13 cm³ * 1g/cm3

                                      = 5.235*10^-13 g

Let there be ‘n’ aerosol particle per cm³ i.e. the aerosol particle concentration is ‘n’ particles/cm³.

So,   n*5.235*10^-13 = 5*10^-7

Or, n = 9.55*10⁵ particles/cm³ (ANSWER)