Quiz 1 - Air Pollution

What is the definition of ppbv?

ppbvi = Vi/Vtot

Write down the equation with consistent units that converts volume fraction, in ppbv, to concentration in ug/m³. a=symbol for volume fraction and b=symbol for concentration

What is a) the best analytical expression/function that defines an aerosol population and b) on what type of graph can we plot this for easy calculations?

a) Lognormal

b) Dp,g and og and Ni, tot where i= number, surface area, volume, mass……

Write down the expression of terminal velocity for ‘creeping flow’ / Stokes regime used in gravitational settling.

Write the expression for Knudsen number.

What is the acceptable range of delta P for a typical cyclone? Write your answer both in units of Pa and in units of H2O.

250-4,000 Pa

1-16 “ H2O

Sketch the following ESP: with 3 mechanical fields, and each mechanical field has 8 bus sections. There are 16 channels in the ESP. Clearly label Lmech field, Lentrance, Lspacing, Ltot, D (channel length), and H (plate height)

A process using gas-liquid extraction is shown below to remove gas A. Streams 1 and 2 are gaseous, whereas streams 3 and 4 are liquid. Gas A is soluble in liquid C whereas gas B is not.

What is a) the % recovery of A (stream 4 is recovery steam) and b) the minimum mass flowrate of C required if A has a solubility of 1 kgA / 10 kgC? You can leave your answers as a fraction, decimal, or percentage but only box your final answer.

Which of the following gases makes up the largest fraction of Earth’s atmosphere?
a) O₂
b) N₂
c) Ar
d) CO₂

b) N2 (78.08)%

What are the six EPA criteria pollutants?

CO, NO₂, SO₂, O₃ (ground-level ozone), Pb, PM (PM₁₀ and PM₂.₅).

Explain why APC devices for aerosols primarily rely on physics, while APC devices for gases rely on chemistry.

Aerosols are physical particles suspended in air, so removal relies on forces like gravity, inertia, and electrostatics. Gases are molecular, so removal typically requires chemical transformation or adsorption.

Using the ideal gas law, explain how to convert acfm to scfm.

Qstd​=Qact​⋅Pstd​/Pact​​⋅Tact​/Tstd​​

where Q = volumetric flow, P = pressure, T = temperature.

Which of the following is not a type of major APC equipment?

a) Baghouse
b) Cyclone
c) Electrostatic precipitator
d) Photocatalytic reactor

d) Photocatalytic reactor

Which distribution is most commonly used today to describe aerosol populations?
a) Power law
b) Gaussian
c) Lognormal
d) Uniform

Lognormal distribution

Why is log-probability paper useful for analyzing aerosol size distributions?

It allows a straight-line fit of lognormal data, making it simple for quick engineering estimates without heavy computation.

Describe one advantage and one disadvantage of settling chambers compared to cyclones.

Advantage: Simple, low-cost, effective for large particles (>100 μm).

Disadvantage: Inefficient for fine particles; requires large space.

What is the equation for the cut diameter, DP,50, in a cyclone (Lapple’s model)?

Which force is not typically considered when analyzing single-particle aerosol dynamics?
a) Gravity
b) Buoyancy
c) Magnetic
d) Electrostatic

c) Magnetic

Cyclone collection efficiency always increases for smaller aerosol diameters. (T/F)

False — Efficiency decreases for smaller particles, since they follow the gas streamlines instead of impacting walls.

What is the primary mechanism by which ESPs remove particles from gas streams?

Electrostatic charging of particles + migration to collection plates

What are two advantages of ESPs over cyclones?

High efficiency for fine particles (<1 μm)

Can handle large gas volumes with low pressure drop

Why are ESPs more effective at collecting fine particles compared to settling chambers?

Electrostatic forces act strongly on small charged particles, whereas gravitational settling is too weak for fine particles.

Write the general form of the Deutsch-Anderson equation for ESP efficiency.

Which of the following is a disadvantage of ESPs?
a) High capital cost
b) High pressure drop
c) Limited operation at high temperatures
d) Frequent clogging from sticky materials

High capital cost

Give two reasons why trace constituents (ppm–ppt levels) are still important in atmospheric chemistry.

They influence ozone formation, greenhouse effect, cloud microphysics, and human health impacts.

A 10 μm spherical aerosol with density 2,500 kg/m³ is falling in air (ρf = 1.2 kg/m³, μf = 1.8×10⁻⁵ Pa·s). Assuming creeping flow (Stokes regime), calculate its terminal velocity.

Explain how the Cunningham correction factor modifies drag force at very small aerosol diameters.

At small sizes (Dp ~ mean free path), slip effects reduce drag, so CC > 1 increases particle velocity compared to continuum flow predictions.

Why might ESP performance decrease when handling “sticky” or high-resistivity dust?

High-resistivity dust resists charge transfer, reducing collection efficiency, and sticky dust causes re-entrainment or maintenance issues.

Compare the pressure drop in ESPs vs cyclones. Why is this difference significant for industrial design?

ESPs have very low pressure drop (<200 Pa), reducing energy/fan costs, whereas cyclones may require >2,000 Pa, making ESPs more energy efficient for fine particle removal despite higher capital cost.