# Air Pollution 315/2010

 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 Assessments2. To discriminate against sources3. To evaluate alternative control strategies4. To compliment ambient monitoring5. To evaluate accidental releases STABILITY 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: Mechanical turbulence due to shearing action of wind and; Temperature gradientComparing actual environmental temperature gradient (lapse rate) to adiabatic lapse rate can help determine possibility of thermal mixing Stability Categories: Stable – does not exhibit much vertical mixing or motionUnstable – mechanical structure is enhanced by thermal structureNeutral – thermal structure neither enhances nor resists mechanical turbulence Lapse Rate is: Rate of decrease in temperature as one ascends through the atmosphereoK/ Km rise (0oK = -273oC) 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 Adiabatic: 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? Unstable Stability letter D? Neutral Stability letters E,F? Stable Slope Factor: From lab/clinical studies, assumes risk at every dose, no safe risk.= Risk/Dose (mg/kg/d)-1 Risk-specific Dose (RsD): for contaminant known to cause cancer= Risk/Slope Factor (mg/kg/day)should be < 1/100,000 for carcinogens TDI: 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 = x10Animals to Humans = x10Chronic NOAEL from subchronic data = x10NOAEL rather than LOAEL = x10MF = x10 (general uncertainty) EDI: Estimated Daily Intake through exposure pathways: inhaled, ingested, etc. Estimated Dose (Air): ED = Ca x IRA x AFinh/BW(mg/kg/day)Ca - concentration of contaminant (mg/m3)IRA - inhalation rate (m3/h)AFinh - inh absorption factor = 1.0BW - body weight Risk (carcinogens): EDI < RsDminimal risk of cancer from exposure to that contaminant Risk (non-carcinogens): EDI < TDIexposure 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/m3) x Fraction of time exposed/Tolerable air [ ] ug/m3or HQ = ED/TDI (ED - calculated without D's and LE)HQ < 1, acceptable risk Incremental Lifetime Cancer Risk (ILCR): Carcinogens (air-borne) (ug/m3)-1ILCR = Air [ ] ug/m3 x Fraction of time exposed x Cancer Unit Risk (ug/m3)ILCR < 1/105 , acceptable risk. Limits of Risk assessment: Lack of studies to back up Lack of long term effects evidenceDifficult to assess risk posed by trace amounts in tissuesWith small doses, dose-response difficult to quantifyIndividual differencesLifestyle differencesConventional approaches inadequate to measure delayed effectsEffects 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: SO2, TRS, NOx, ppm (TSP, PM10, PM2.5, & dustfall), PAHs, PCBs, VOCs, fluoridation rate, meteorological (wind speed/direction, temp, solar radiation) Sampling System Design: Temperature stability of shelterLocation of sampling probe(s)Manifold or sample inlet line systemLength of probeProbe materialFilters/fittings Site Management: Determine frequency of routine site visitsProvide trainingPlan approp. level of surveillancePlan equipment operations and data checkingCalibration checks (daily, manual, multi-point)Traceability, unique identifiersSOPs VOC Monitoring Summa Cannister, fills after 24 hours. TSP and Metals monitoring high vol sampler, quartz filterQ = 40-60 ft3/min PAH and PCB monitoring: high volume sampler, PUF/XAD moduleQ = 7.9 ft3/min PM10 monitoring: high vol sampler, quartz filter, selective inletbig round topQ = 40 ft3/min PM2.5 monitoring low vol sampler, PTFE filter, size selective filterQ = 16.7 L/min STPA-AAMP Sydney Tar Ponds Agency - Ambient Air Monitoring Program As Fg accelerates particle downward, speed increases and FD: Drag Force increases. Net force: Fg - FD: decreases with acceleration (eventually reaching 0) Fg is constant, 9.81 m2/sec, FD: increases with speed. Stokes Law: When net force = 0, then FD = FgIf 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) = ut. Optimal Particle Ranges: Settling Chamber Cyclone Wet scrubber Fabric filter Electrostatic precipitator Settling Chamber: 40-10,000 umCyclone: <10-20 umWet scrubber: 0.1 - 30 umFabric filter: 0.01 - 20 umESP: 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 balancedSignificant 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: AdsorptionAbsorptionCondensationCombustion Manual used on Sydney Tar Ponds Project AQ monitoring: Operations Manual for Air Quality Monitoring in Ontario Authornewtwit ID15266 Card SetAir Pollution 315/2010 DescriptionAir Pollution Exam - Public Health 2010 Updated2010-04-21T02:09:52Z Show Answers