Air Pollution 315/2010
Card Set Information
Air Pollution 315/2010
Air Pollution Exam - Public Health 2010
What is Air Pollution Dispersion Modeling ?
A model provides a fundamental link between emissions and air quality changes by simulating transport, dispersion, transformation, and deposition.
Why do we model air pollution?
1. Emission Assessments
2. To discriminate against sources
3. To evaluate alternative control strategies
4. To compliment ambient monitoring
5. To evaluate accidental releases
Degree of stability must be known if we are to estimate the ability of the atmosphere to be able to disperse pollutants from anthropogenic sources.
Stable atmospheres do not allow much vertical mixing. As a result, pollutants near the earth’s surface tend to stay there
Mixing is dependant upon
due to shearing action of wind and;
Comparing actual environmental temperature gradient (lapse rate) to adiabatic lapse rate can help determine possibility of thermal mixing
– does not exhibit much vertical mixing or motion
– mechanical structure is enhanced by thermal structure
– thermal structure neither enhances nor resists mechanical turbulence
Lapse Rate is:
Rate of decrease in temperature as one ascends through the atmosphere
K/ Km rise (0
K = -273
Dry adiabatic lapse rate
Rate of temperature decrease of parcel of air as it rises
Environmental lapse rate
Temperature gradient of ambient air as changes with altitude.
What is zero drift?
Drift dictates the frequency of calibration.
Zero drift is the change in response to zero pollutant concentration, over 12 and 24 hours of continuous unadjusted operation
What is span drift?
the percent change in a response to a pollutant concentration over a 24-hour period of continuous unadjusted operation
Occurring without the addition or loss of heat.
Unstable (B-C) conditions:
Atmospheric lapse rate cooling faster then adiabatic lapse rate in plume.
Stability letters ABC?
Stability letter D?
Stability letters E,F?
From lab/clinical studies, assumes risk at every dose, no safe risk.
= Risk/Dose (mg/kg/d)
Risk-specific Dose (RsD):
for contaminant known to cause cancer
= Risk/Slope Factor (mg/kg/day)
should be < 1/100,000 for carcinogens
Tolerable Daily Intake (Rfd - reference dose)
for non-cancer effects; non-carcinogens
= NOAEL/(UF1 x UF2 x ... x MF)
Uncertainty Factors for TDI:
Heterogeneous Population = x10
Animals to Humans = x10
Chronic NOAEL from subchronic data = x10
NOAEL rather than LOAEL = x10
MF = x10 (general uncertainty)
Estimated Daily Intake through exposure pathways: inhaled, ingested, etc.
Estimated Dose (Air):
ED = C
- concentration of contaminant (mg/m
- inhalation rate (m
- inh absorption factor = 1.0
BW - body weight
EDI < RsD
minimal risk of cancer from exposure to that contaminant
EDI < TDI
exposure to contaminant likely does not pose signif risk to human health
Slope-factor vs. TDI
Cancer risk per bite vs. Threshold number of bites resulting in toxic effect.
Hazard Quotient (HQ):
Non-carcinogens (air-borne contaminant)
HQ = Air [ ] (ug/m
) x Fraction of time exposed/Tolerable air [ ] ug/m
HQ = ED/TDI (ED - calculated without D's and LE)
HQ < 1, acceptable risk
Incremental Lifetime Cancer Risk (ILCR):
Carcinogens (air-borne) (ug/m
ILCR = Air [ ] ug/m
x Fraction of time exposed x Cancer Unit Risk (ug/m
ILCR < 1/10
, acceptable risk.
Limits of Risk assessment:
Lack of studies to back up
Lack of long term effects evidence
Difficult to assess risk posed by trace amounts in tissues
With small doses, dose-response difficult to quantify
Conventional approaches inadequate to measure delayed effects
Effects only seen in synergism
Continuous Emission Monitors (CEMs):
have built in calibration gases to correct for zero drift and span drift daily i.e. continuous calibration.
Parameters monitored at station:
, TRS, NO
, ppm (TSP, PM
& dustfall), PAHs, PCBs, VOCs, fluoridation rate, meteorological (wind speed/direction, temp, solar radiation)
Sampling System Design:
Temperature stability of shelter
Location of sampling probe(s)
Manifold or sample inlet line system
Length of probe
Determine frequency of routine site visits
Plan approp. level of surveillance
Plan equipment operations and data checking
Calibration checks (daily, manual, multi-point)
Traceability, unique identifiers
Summa Cannister, fills after 24 hours.
TSP and Metals monitoring
high vol sampler, quartz filter
Q = 40-60 ft
PAH and PCB monitoring:
high volume sampler, PUF/XAD module
Q = 7.9 ft
high vol sampler, quartz filter, selective inlet
big round top
Q = 40 ft
low vol sampler, PTFE filter, size selective filter
Q = 16.7 L/min
Sydney Tar Ponds Agency - Ambient Air Monitoring Program
accelerates particle downward, speed increases and F
Drag Force increases.
Net force: F
decreases with acceleration (eventually reaching 0)
is constant, 9.81 m
increases with speed.
When net force = 0, then F
If the particles are falling in the viscous fluid by their own weight
due to gravity, then a terminal velocity, also known as the settling velocity, is
reached when this frictional force combined with the buoyant force exactly balance the gravitational force.
The result is settling velocity (or terminal velocity) = u
Optimal Particle Ranges:
: 40-10,000 um
: <10-20 um
: 0.1 - 30 um
: 0.01 - 20 um
: 0.001 - 10 um
Electrostatic Precipitators work by:
giving particles an electrostatic charge then puts them in an electrostatic field that drives them to a collecting wall.
Two types of filters are:
Surface filters (coffee filter - form a cake) &
Depth filters (HEPA - brownian diffusion)
Brownian diffusion - 2 important effects:
Rate of collisions are not balanced
Significant force in the imbalanced direction
Scrubbers collect particles:
in dirty gas stream with liquid drops (eg. ventruri scrubber)
Particles collide with droplets, separated in cyclone
4 ways of reducing pollutants:
Manual used on Sydney Tar Ponds Project AQ monitoring:
Operations Manual for Air Quality Monitoring in Ontario