CIH Community Exposure Reference
Chapter 8 in one order that follows the pollutant: where it comes from, how it travels, what reaches people, how it is measured, and how it is cleaned or contained, ending with spill response and a self-test. Each table marks the fact an exam question most often leans on in red.
How to use this page
BGC’s Community Exposure subject area covers air pollution, air-cleaning technology, ambient air quality, emission source sampling, atmospheric dispersion, ambient monitoring, health and environmental effects, and emergency planning and responseBGC. The sections below run in the order a real problem unfolds, so each one gives the next its inputs.
- Red text is the recognition cue: the keyword or number a question is most likely to hinge on.
- Yellow cards are memory tricks and traps.
- This is a study aid in original wording, not a copy of any course text or BGC material. Sources are on the CIH references page, and the reasoning behind the order is in the Ch.8 journal entry.
01 Where Pollutants Come From
Start here: you cannot judge dispersion or control until you know whether a pollutant is emitted or formed.
Why ambient limits are stricter than TLVs. A TLV assumes a healthy adult worker exposed about 40 hours a week. Ambient standards protect the whole public, including children, older people and people with asthma, breathing the air all 168 hours of the week. EPA’s national standards come in two kinds: primary standards protect health, and secondary standards protect welfare (visibility, crops, animals, buildings)EPA.
| Source split | Meaning | Examples |
|---|---|---|
| Natural | Released without human activity | Volcanoes (SO2, ash), wildfires, wind-blown dust, sea spray, pollen, VOCs from vegetation |
| Anthropogenic | Released by human activity; dominates in industrial areas, though the share differs by pollutant | Power plants, industry, heating, agriculture |
| Mobile (a kind of anthropogenic) | Vehicles and engines | The largest source of outdoor carbon monoxide: incomplete combustion in enginesEPA |
The pollutants below are the criteria pollutants regulators trackEPA plus the toxic and organic species that come up in CIH questions. Nitrogen oxides and VOCs are primary pollutants, but they are also the precursors of the secondary ones.
| Type | Meaning | Examples | CIH study cue |
|---|---|---|---|
| Primary | Emitted directly from an identifiable source (tailpipe, stack, fire, dust from soil). | Carbon monoxide (incomplete combustion); sulfur dioxide (coal or oil burning); NO and NO2 (high-temperature combustion); particulate matter and coarse dust; lead; VOCs such as benzene and formaldehyde; toxic metals (mercury, cadmium, arsenic). | If you can point at the source, it is primary. |
| Secondary | Not emitted; formed in the air when primaries react with sunlight, moisture and each other. | Ground-level ozone; photochemical smog (ozone, PANs, aldehydes); acid deposition (sulfuric and nitric acids from SO2 and NOx); secondary fine particles (ammonium sulfate and nitrate); secondary organic aerosols; nitric acid vapor; part of ambient formaldehyde. | If the question says it forms in the atmosphere, on hot sunny days, or by reaction, it is secondary. |
02 How Pollutants Travel
Atmospheric stability decides the plume shape, and the plume shape decides who is exposed at ground level.
Stability comes from comparing the real temperature profile with the dry adiabatic lapse rate, the rate a rising parcel of dry air cools: 9.8 °C per km (5.5 °F per 1,000 ft)NWS.
| Real air cools with height… | Name | Stability | Pasquill class | Mixing |
|---|---|---|---|---|
| Faster than 9.8 °C/km | Superadiabatic | Unstable | A–C (strong sun, light wind) | A lifted parcel keeps rising: strong vertical mixing |
| At about 9.8 °C/km | Adiabatic | Neutral | D (overcast or windy) | Parcel neither rises nor sinks on its own |
| Slower than 9.8 °C/km | Subadiabatic | Stable | E–F (clear night, light wind) | Vertical motion is damped |
| Warms with height | Inversion | Very stable | F | A lid: pollutants below it are trapped |
| Plume | Atmosphere | What it looks like | Ground-level effect | Exam cue |
|---|---|---|---|---|
| Looping | Very unstable (strong solar heating, convection) | Wavy, looping up and down | Highly variable; can touch the ground in bursts | Sunny, turbulent, large vertical swings. |
| Coning | Neutral (moderate wind, overcast) | Cone spreading equally in both directions | Fairly predictable | Neutral; equal horizontal and vertical spread. |
| Fanning | Very stable (strong inversion) | Thin, flat ribbon; almost no vertical spread | Usually low near the stack; can matter downwind or at terrain and tall buildings | Inversion; horizontal spread, little or no vertical spread. |
| Lofting | Stable below the plume, unstable above | Spreads upward, little downward mixing | Lowest ground-level concentration | Stable below, unstable above; plume goes up. |
| Fumigation | Unstable below the plume, stable (inversion) above | Pushed down toward the ground | Highest ground-level concentration | Inversion lid above; downward mixing; plume reaches the ground. |
03 What Reaches the Community
Two calculation habits: dilute the emission, and correct the unit conversion for the actual air.
| Actual vs reference | Effect on molar volume | Calculated ppm |
|---|---|---|
| Higher temperature | Larger | Higher |
| Lower pressure | Larger | Higher |
| Lower temperature or higher pressure | Smaller | Lower |
Two nearby formulas from the ventilation chapters also appear in community questions. Well-mixed room: V·dC/dt = G + Q·Cin − Q·C (plus any removal term), so generation rate, airflow, supply-air concentration and room volume matter, while air density is not a variable. Simplified outdoor air: a 20 cfm-per-person rule of thumb is a shortcut; ASHRAE 62.1 actually adds a people component (Rp) and an area component (Ra).
04 How to Measure It
Match the pollutant to its sampler and its analytical method.
These are the classic methods taught for the exam. Current regulatory monitoring uses EPA-designated reference or equivalent methodsEPA, many of them automated, so treat this table as recognition practice.
| Pollutant | Collection or measurement | Analytical method |
|---|---|---|
| Total suspended particulate (TSP) | High-volume sampler with filter | Gravimetric: mass gain on the filter |
| Lead | High-volume sampler with filter | Acid extraction, then atomic absorption |
| Sulfur dioxide | Bubbler or impinger with absorbing solution | West-Gaeke colorimetric method |
| Ozone | Reaction chamber | Chemiluminescence (light from the ozone reaction, read by a photomultiplier) |
| Carbon monoxide | Gas absorption cell | Nondispersive infrared (NDIR) absorption |
| Hydrocarbons | Gas intake and detector | Flame ionization detector, often with gas chromatography |
| Nitrogen dioxide | Bubbler (colorimetric) or reaction chamber | Saltzman colorimetric method, or chemiluminescence (NO reacts with ozone; NO2 is measured after conversion to NO) |
05 Stack Sampling and Isokinetic Flow
A stack sample is only representative if the probe takes gas at the speed the stack is moving.
Stack testingEPA aims for isokinetic sampling: the probe draws gas at the same velocity as the gas in the stack (Vs = Vd). Coarse particles have inertia and cannot follow streamlines that bend around the probe, so a velocity mismatch changes which particles get in.
| Condition | Name | What the probe does | Particle bias | Reading |
|---|---|---|---|---|
| Vs = Vd | Isokinetic | Takes a true slice of the stack gas | Representative | Accurate |
| Vs < Vd | Sub-isokinetic | Draws gas slower than the stack moves | Coarse particles over-sampled | Concentration reads high |
| Vs > Vd | Super-isokinetic | Draws gas faster than the stack moves | Coarse particles under-sampled; fines over-represented | Concentration reads low |
06 Cleaning the Emission
Pick the device from particle size and physical state first; then check its weak spot.
| Device | Typical target size | How it works | Best for | Weak spot | Pressure drop (typical) |
|---|---|---|---|---|---|
| Cyclone (dry centrifugal) | Coarse, roughly 5–15 µm and larger | Spinning vortex throws heavy particles to the wall and into a hopper | Coarse dust: woodworking, quarry, cement handling; pre-cleaner upstream of finer devices | Efficiency drops below about 10 µm; fails on fume and smoke; depends on design flow; abrasive dust wears the casing | Low to moderate (about 2–6 in. w.g.) |
| Venturi scrubber (high-energy wet) | Fine and submicron, about 0.1–1 µm | Gas accelerated through a narrow throat; injected water atomizes into droplets that capture particles | Metal fume, smoke and mist; hot, sticky, flammable or explosive streams | Very high energy use; produces wastewater or slurry; corrosion; needs a mist eliminator | Very high (30–100+ in. w.g.) |
| Baghouse (fabric filter) | About 0.1 µm up to 20+ µm | Dirty air passes through fabric bags that trap dry dust | Dry dusts: grain, concrete and asphalt batching, powders | Condensation blinds the bags; hot gas limits; combustible dust needs explosion protection; sticky or wet streams | Moderate (about 3–6 in. w.g.) |
| Electrostatic precipitator (ESP) | Ultrafine, about 0.01–1 µm | High-voltage wires charge particles, which stick to grounded plates and are rapped off | Huge airflows with smoke and ash: power plants, incinerators, steel | Dust resistivity (too low: particles re-enter the air; too high: back corona); ozone and spark risk with explosive dust or gas; high capital cost and footprint | Low (about 0.5–2 in. w.g.) |
Ranges and pressure drops are typical teaching valuesCCOHS; real equipment varies with design and operating conditions.
07 Water Pollution and Hazardous Waste
The same source-to-control logic, applied to what goes into water and what goes to disposal.
| Topic | Key idea | CIH study cue |
|---|---|---|
| Point vs nonpoint source | A point source is a discrete conveyance such as a pipe, ditch or channel (concentrated animal feeding operations count too). Nonpoint pollution is diffuse runoff from farms, streets and lawns | Point sources discharging to US waters need an NPDES permit under the Clean Water ActEPA |
| Biochemical oxygen demand (BOD) | Oxygen that microbes use to break down organic matter in water, usually measured over 5 days (BOD5) | High BOD → low dissolved oxygen → fish kills. Sewage and food-processing waste are high-BOD |
| Wastewater treatment | Primary: physical settling. Secondary: biological treatment that lowers BOD. Tertiary: nutrient removal and polishing; then disinfection | Primary = physical, secondary = biological |
| RCRA hazardous waste | Listed: F (non-specific sources, such as spent solvents), K (specific industries), P (acutely hazardous discarded chemicals), U (other discarded chemicals). Characteristic: ignitable, corrosive, reactive or toxicEPA | RCRA manages waste “cradle to grave” from generation to disposal. Characteristics: I-C-R-T |
| CERCLA (Superfund) | Passed in 1980 to clean up contaminated sites; responsible parties pay, and the fund covers sites with no viable responsible partyEPA | RCRA = today’s waste. CERCLA = yesterday’s contamination |
08 When It Goes Wrong: Spills and Incident Command
Community emergencies reuse the same ideas: dispersion, terrain, and a fixed command structure.
Reasoning through a release
Emergency exposure guidelines
TLVs and PELs are built for repeated working-day exposure. A one-time release to the public needs limits built for a single short exposure.
| Level | ERPG (AIHA): up to 1 hourNOAA | AEGL (EPA): 10 min, 30 min, 1 h, 4 h and 8 hEPA |
|---|---|---|
| 1 | No more than mild, transient effects, or a clearly objectionable odor | Notable discomfort or irritation; transient and non-disabling |
| 2 | No irreversible or serious effects, and no symptoms that would stop people protecting themselves | Irreversible or serious long-lasting effects, or an impaired ability to escape |
| 3 | No life-threatening effects | Life-threatening effects or death |
Emergency Response Guidebook (ERG)
The ERGPHMSA is a first-response tool for the opening phase of a transportation incident. Its colour-coded sections work as a lookup chain that ends at the action pages.
| Section | Role | What you find |
|---|---|---|
| White (front) | Setup | How to use the book, shipping papers, placards, rail and trailer identification |
| Yellow | Look up by number | Four-digit UN/NA ID numbers in order, each pointing to a guide |
| Blue | Look up by name | Material names in alphabetical order, each pointing to a guide |
| Orange | The action pages | The numbered Safety Guides (numbered 111–172 in recent editions): potential hazards, public safety, and emergency response for fire, spill or leak, and first aid |
| Green | Distances | Initial isolation and protective action distances for toxic inhalation hazard materials and water-reactive materials |
| White (back) | Specialized guidance | Contacts, pipeline safety, improvised explosive and CBRN response information |
Each Safety Guide opens with the greater danger first, health or fire and explosion; the public safety block gives isolation and protective equipment; the response block gives the tactical steps.
Incident Command System (ICS)
ICSFEMA is a standard, modular, top-down structure so responders from many agencies can work together.
| Level | Role | Job |
|---|---|---|
| Command | Incident Commander | Overall responsibility: sets objectives and directs tactics |
| Command Staff | Safety Officer | Monitors hazards; may stop or alter unsafe actions |
| Command Staff | Public Information Officer | Single point of contact for media and the public |
| Command Staff | Liaison Officer | Coordinates with assisting outside agencies |
| General Staff | Operations | Runs the tactical response on scene |
| General Staff | Planning | Gathers information, tracks resources, prepares the incident action plan |
| General Staff | Logistics | Facilities, transport, supplies, food, medical and communications |
| General Staff | Finance/Administration | Costs, claims, procurement, records |
| General Staff (optional) | Intelligence/Investigations | Used for criminal, terrorist or complex incidents |
09 Self-Test
Original scenarios. Cover the answer, decide, then open it.
1A coastal city’s ozone monitor peaks at 3 p.m. on a hot, cloudless day, but traffic volume peaks at 8 a.m. Is ozone a primary or secondary pollutant, and why does the peak come late?
Secondary. Ozone is not emitted; it forms from NOx and VOCs in sunlight, so it builds through the day and peaks in the afternoon.
2On a clear, calm night with a strong ground-level inversion, a stack plume is a thin flat ribbon that barely spreads vertically. Name the plume and say what to watch for near the ground.
Fanning (very stable). Concentrations are usually low near the stack, but terrain or tall buildings can bring the ribbon down, so check downwind obstacles.
3Just after sunrise, the ground warms under an inversion that still sits above a smelter stack. The plume is pushed down. Which plume, and what is the ground-level result?
Fumigation: unstable below, stable above. This gives the highest ground-level concentrations.
4A stack emits 480 mg/m3 and the dilution factor to the nearest homes is 12,000. What concentration reaches the homes?
480 ÷ 12,000 = 0.04 mg/m3.
5A stack tester pulls gas through the probe more slowly than the gas moves in the stack. Which particles are favored, and which way does the reading err?
Sub-isokinetic: coarse particles are over-sampled and the concentration reads high.
6A foundry vents hot, sticky, submicron metal fume with some mist. Which device is the natural choice, and why not a cyclone or a baghouse?
A venturi scrubber. A cyclone is ineffective on submicron fume, and a baghouse is blinded by sticky, wet or hot streams.
7A plant vents very fine combustible organic dust plus toxic fume beyond the fence line. Which two common devices would you rule out first?
The ESP, because its electrical discharge is an ignition source for combustible dust, and the cyclone, which cannot capture fines. That leaves a baghouse with explosion protection or a wet scrubber; the scrubber has no ignition source and also captures fume.
8An air sample is converted from mg/m3 to ppm at 95 °F and 29.70 in Hg, compared with reference conditions of 68 °F and 29.92 in Hg. Is the calculated ppm higher or lower than expected?
Higher: the air is hotter and at lower pressure, so the molar volume is larger and the same mass concentration gives a higher ppm.
9Morning air cools at 12 °C per km of height. Is the atmosphere stable or unstable, and what does that do to a plume?
Unstable (superadiabatic: faster than 9.8 °C/km). Strong vertical mixing gives a looping plume.
10A plant raises its stack from 30 m to 60 m with the same emissions. What happens to the maximum ground-level concentration, and why?
It falls: a higher effective stack height gives the plume more distance to spread before it reaches the ground.
11A drum of unused, off-spec pesticide listed as acutely hazardous must be discarded. Which RCRA list applies?
The P-list: acutely hazardous, unused commercial chemical product.
12An emergency planner must draw the zone where the public could lose the ability to escape during a 1-hour chlorine release. Which guideline level?
ERPG-2 (or the 60-minute AEGL-2).
13Eight responders report directly to one supervisor at a spill. What does ICS suggest?
The span of control is exceeded (3–7, ideally 5), so create a subordinate level such as a division, group or branch.
These are original practice scenarios written for this page. They are not BGC questions and do not predict exam content.