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

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)

What are Air Particles? Particles in Air Dispersed matter: solid or liquid particles Aggregates range from molecular clusters of 0.005 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.)

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

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

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)

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

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).

PM10 Hi-Vol Sampler Works same way except 1. 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.

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 - http://www.tnrcc.state.tx.us/cgi-bin/monops/particulates 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.

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 0.001 -1 mm Nephelometric turbidity units NTU Turbidity: regulated and enforced Turbidity is what is regulated and enforced. http://www.ecy.wa.gov/programs/wq/plants/management/joysmanual/4tss.html

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

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

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

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

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

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!

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

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: 998.2 g/L

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

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

Volume/Volume and Mole/Mole Concentration Units Ideal Gas Law R=0.082056 (L atm) / (K mol)

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

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

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.

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)

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 0.005 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,