1. CEE 160L– Introduction to Environmental Engineering and Science
Lecture 2
Units of Concentration

2. How do we express concentration?
Quantity
Mass or weight
Volume
Moles
Concentration
moles/L (liquid)
g/m3 (gas)
mg/g (solid)
% (by weight or by volume)

3. What are Air Particles? Particles in Air
Dispersed matter: solid or liquid particles
Aggregates range from molecular clusters of mm to coarse particles of 100 mm
Dusts: larger particles that settle quickly
Collect in dustfall jars for specified time
Dustfall jar is a large open container used to collect larger particles from the air. The particles might be monitored for total solids (total weight) or the composition (% of lead, zinc, dioxins, etc.)

4. What Do Particles Look Like?
Spherical Fe-rich Particle
Carbon Chain Agglomerate
1 µm
7500X
Regular or irregular shapes
Used with permission of Professor Cliff Davidson, CMU

5. How do we measure particle concentration in air?
Draw known air volume through preweighed filter.
Weigh particles on filter.
High-Volume Sampler
Particles greater than 10 um can be removed by the hair/linings of the nose, or worked to the back of the throat by the cilia and removed by swallowing or spitting. Particles smaller than 10 um may be able to penetrate deep into the lungs.
Clean and dirty air filters

6. High-Volume (Hi-Vol) Sampler
Works like a vacuum cleaner
Air sucked in from top passes through a filter
Filtered weighed before and after to measure Total Suspended Particles (TSP)

7. Particulate Size: PM number
PM 10: Particles < 10 mm diameter
Coarse
PM 2.5: Particles < 2.5 mm diameter
Fine
PM 10 and PM 2.5 regulated by National Ambient Air Quality Standards (NAAQS)
mg/m3

8. Why is PM a Concern? PM10 can penetrate deeply into lungs! Alveoli
Tiny air sacs in lungs
PM aggravates existing respiratory and heart diseases
PM damages lung tissue
Some PM carcinogenic
Estimated PM2.5 regulation prevents 15,000 premature deaths per yr.
Deposition in the lungs (alveoli) is most effective at particle sizes between 2 and 4 um.
Very small particles have lower deposition rates because they can go in and then right back out (don’t get caught in lungs).

9. PM10 Hi-Vol Sampler Works same way except1. 2. 3.
Works same way except
Air sucked into super chamber (1)
Passes through vent tubes into impaction chamber (2) where it swirls around leaving behind large particles
Air minus large particles pulled through vents into pre-filter chamber (3)
And then through filter (4) that captures PM10 particles 4.

10. PM10
How measured?
PM 10 inlet on hi-vol sampler
Set air volumetric flowrate such that
Particles > 10 mm impact side and are discarded
Particles < 10 mm reach filter for weighing
Why do we need PM 10 Inlet?
What happens to particle concentration if air T increases?
PV=nRT
Same # of particles, but air volume increases
Particle concentration decreases
Show Ambient Air Quality Standards on Overhead
Data -
PM 2.5: 15 g/m3 AAM; 65 g/m3 24 hr (AAM=annual arithmetic mean)
PM10: 50 g/m3 AAM; 150 g/m3 24 hr.
PM 2.5 Standard is estimated to prevent 15,000 premature deaths each year (EPA).
Hospital admissions for congestive heart failure increase 8% for each 100 g/m3 increase in PM 10.
We need the PM10 inlet to measure the particle concentration for the standards. Otherwise, we are just measuring total particulate matter.

11. Particles in Water 3 size classes Total Suspended Solids (TSS)
> 1 mm
mg/L
Filtration
Total Dissolved Solids (TDS)
< 1 mm
Remove liquid from known volume, measure mass of dried residue
Colloidal Solids mm
Nephelometric turbidity units
NTU
Turbidity: regulated and enforced
Turbidity is what is regulated and enforced.

12. Measuring Turbidity Turbidity Cloudiness of a solution
Photometer measures transmitted light
More particles, less transmitted light
Nephelometer measures scattered light
More particles, greater NTUs

13. Turbidity Follows Beer’s Law Iout=Iinexp(-aC) T = log10(Io/I)=2.303aC
C=concentration
Increasing light scatter

14. What are Solutions? Normally think of solutions as liquids
But can be gases, liquids and solids
Solute = substance that dissolves
Solvent = substance in which solute dissolves
Example: Salt water

15. Units Used to Measure Mass
Mass/Mass
Mass/Volume
Volume/Volume
Partial pressure of gasses
Mols/Volume

16. 1. Mass/Mass Concentration Units
NOT TEMPERATURE OR PRESSURE DEPENDENT
Typical Units
mg/kg
Percent (by mass)
ppm = parts per million
ppb = parts per billion

17. Mass/Mass Concentration Units
ppm (by mass)
Mass of solute per 106 units of total mass of sample
X mg solute/kg sample
ppb (by mass)
Mass of solute per 109 units of total mass of sample
X mm/kg sample
Use any consistent
units of mass!

18. 2. Mass/Volume Concentration Units
Typical Units:
For Air: mg/m3 or g/m3
For Water: mg/L or g/L or mole/L
1 ppm(mass) = 1mg solute/kg solution * 1 kg solution (water)/L solution (water) = 1 mg solute/L solution
In other words: ppm (by mass) * density of water = mass/volume

19. 1 mg/L = 1 ppm (mass)? Convert mass/volume to mass/mass
1mg/L = 10-3g/L
Density of water rw=1000 g/L
10-3g/L x (1L/1000g) = 10-6 or 1 ppm
Densities of liquids sensitive to temperature
Density of pure water at 5 C: 1,000 g/L
Density of pure water at 20C: g/L

20. 3. Volume/Volume and Mole/Mole Concentration Units
ppm (by volume)
Volume of solute per 106 units of total volume of sample
X mg solute/kg sample
ppb (by volume)
Volume of solute per 109 units of total volume of sample
X mm/kg sample

21. ppm/ppb Units in Air Air contaminants are often given in ppm/ppb
By convention, these are volume/volume units
Even though they don’t say ppmv/ppbv
I will always specify ppmm or ppmv
But, be aware of this convention for textbooks

22. Volume/Volume and Mole/Mole Concentration Units
Ideal Gas Law
R= (L atm) / (K mol)

23. Volume/Volume and Mole/Mole Concentration Units
Ideal Gas Law – Useful Properties
Ppmv is in independent of T and P since these variables cancel out.
Because air acts like an ideal gas then the ratio pollutant volume to air volume are:
(1) the same as ratio of moles and
(2) independent of P and T

24. How does this work?
Very small airborne particles (red) are suspended by thermally induced kinetic movement of air molecules (blue).
If you increase the temperature then you increase the kinetic energy of the air molecules that proportionately further disperses the pollutant particles.
Lower T
Higher T

25. 4. Partial Pressure of Gasses
The total pressure exerted by a gas mixture is
The sum of the partial pressures exerted by each component in a mixture.

26. Partial Pressure
By the ideal gas law, pressure is directly proportional to the number of moles of gas.
Not the type of gas molecules
Example:
(Partial pressure of i)

27. 4. Mole/Volume Common units for compounds dissolved in water
Molarity, M
# of moles of compound per liter of solution
Brackets indicate molarity
[Na+]=1.5M
Also units of mM, mM, nM
Note: Maximum Concentration Limit for TCE in water is mg/L = 5 ppb
Solution to Problem:
Recall that 5 ppm for a liquid phase (with density of approximately 1000 g/L) is really 5 ppm by mass. Also, recall that for dilute solutions of water, 1 ppm by mass is the same as 1 mg/L since the density of water is approximately 1000 g/L.
Therefore,