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Suburban air quality monitoring
Measuring Air Pollution in the Mid-Atlantic United States
Bebhinn DoMeteorologist, NC DAQ
Some slide material provided through K.G. Paterson, Ph.D., P.E. ©2007 via contract with MARAMA
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Did You Know?
There are more than 4000 air quality monitoring sites in the United States.
Most are monitoring several air pollutants, every hour, every day.
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Course GoalsBy the end of this session, you will
Know some modern ways to measure key pollutants in emissions and ambient air
Understand the trade-offs in monitoring site selection Be familiar with ways to monitor air quality remotely Be aware of a few data analysis methods
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Discussion
You’re a government leader who has just been given funding to place monitors in your state.
Where do you place your monitors?
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Monitoring
Critical measurement decisionsLocation• Infrastructure• Access• Interference• Representativeness• Supporting data
Resolution• Time and space• Data needs• Analysis skills• Data storage• Reporting
Methodology•Accuracy•Sensitivity•Reliability•Utility
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MonitoringState regulatory agencies routinely monitor the
ambient concentration and emissions of several pollutants.
Concentrations•Carbon monoxide (CO)•Nitrogen dioxide (NO2)•Ozone (O3)•Sulfur dioxide (SO2)•Particulate matter (PM10, PM2.5)•Lead (Pb)
Emissions•Carbon monoxide (CO)•Sulfur dioxide (SO2)•Particulate matter (PM10, PM2.5)•Nitrogen oxides (NOx)•Volatile organic compounds (VOCs)•Ammonia (NH3)
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MonitoringEach pollutant requires a different
measurement methodology (analysis + technology)
Common featuresAutomated and continuous operationReal-time measurementData recording and/or transmission
Methodologies and instrumentation are approved and recommended by the U.S. EPA
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Monitoring: EquipmentThermo Electron Company’s (formerly Rupprecht
& Patashnick) TEOM allows continuous real-time measurement of ambient PM
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Monitoring: EquipmentEnvironnement S.A. UV Absorption
Ozone Analyzer Model O342MUser programmableRemote maintenance
and data acquisitionBuilt-in storage of two
month’s data0.4 to 500 ppb
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MonitoringContinuous emission monitoring (CEM)
Required of most power plants under the Acid Rain Program (many other facilities via the New Source Performance Standards)
Measured pollutants: SO2, NOx, opacity
Importance: • Verifying emissions for trading programs
• Compliance
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MonitoringEmission monitoring has unique challenges
Sampling is in stack discharge airstreamEnvironment can be extremeSensors are specific to source facilityIntegrated to operations of facility
source: Apex Instruments, Apexinst.com
Mounted stack sampler Mobile stack sampler
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Monitoring
Remote sensing analyzes the air from a distant location
Current techniquesLidar (Light detection and ranging)
• Remote target hit with pulsed lasers at two wavelengths
• Detects gases with good light absorption: SO2, O3, NH3, H2S
Satellite• Can cover large areas, but interferences are challenging
• Limited to a pollutants with strong absorption signals: CO, O3
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MonitoringMOPITT (Measurements of Pollution in the
Troposphere) sensor on NASA's Terra satellite is measuring CO around the planet (data is typically mid-troposphere)
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LocationMonitoring sites are usually not selected in
isolation. Rather, the site is one of many within a monitoring network.
Monitoring network strengths More robust assessment of air quality Impacts of new sources Air quality trends and patterns
Site selection criteria
Purpose of measurementsPopulation density Pollutants being measuredProximity to other monitoring sites Emission inventory dataUtility to modeling efforts
Climatological dataTopographyAvailability of land and powerSecurityObstruction-free samplingCost
Tough to find the “perfect” location. Compromises are always made.
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LocationMonitoring sites do not always have the same
purpose, though.The monitoring site is established to understand the
air quality at a particular area of interest. For example, Neighborhood, community, or regional levels Urban or rural levels Background levels or maximum impact
A good question to ponder prior to using air quality data: is the site representative of the intended purpose?
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Location
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Location
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Location
Monitoring site locations for criteria air pollutants within the Mid-Atlantic
Can you determine the logic behind the placement of these
monitoring sites?
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Data AnalysisStatistical methods answer questions
quantitatively. Examples of uses and typical questions:
Summarize measurements (e.g. What is the average concentration today, 24-hr average?)
Reveal patterns and trends (e.g. Is the air quality getting better or worse?)
QA/QC (e.g. Is that high pollutant concentration an outlier or due to an unusual source?)
Regulatory compliance (e.g. Does the air quality meet national standards?)
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Data AnalysisQuality assurance (QA) program goals
Assessment of collected air quality dataImprovement of data collection process
Quality control (QC)Operational procedures, specs, and standards
1. Sampling method description2. Instrument configuration3. Calibration procedures4. Zero checks5. Corrective limits and actions6. Preventative maintenance7. Data recording8. Documentation of QA activities
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Data Analysis
There are many data analysis methods among statistical methods. We will examine only a couple of these strategies:Identification of outliersData smoothing
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Data AnalysisIdentification of Outliers
Outliers are extreme (high or low) values that diverge widely from the main body of a data set
Outliers can have significant influence on other statistics, e.g. average, standard deviation
Sources of outliers:• faulty instrument• transcription error• technician/lab error• misread instrument• inconsistent sampling• methodology• blunders• cover-up
Or........the outlier could reflect real, but extreme, conditions
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Data Analysis
Smoothing A way to eliminate the roughness (variability or
noise) in the data that blurs the underlying pattern.
We can smooth data using several techniques, let’s consider one• Moving average is a way to smooth the data by
determining an average based on the current and historical values (the most recent “X” data points).
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Data AnalysisMoving Average
Estimate 3 year average of 4th highest daily 8-hr periods
Compare to standard (0.08 ppm)
To assess a long-term record, a tableor graph of 3-year moving averages would be helpful
Ozone from Lewes, DelawareMonitoring Site
Any Question?
Thanks for making this a great class!
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Post Test
1. In selecting a site to locate an air quality monitor, which of the following characteristics should be considered?
a) Securityb) Proximity to peoplec) Topographyd) Water supply
2. Which pollutant is measured by a TEOM?a) Ozoneb) Sulfur dioxidec) Nitrogen dioxided) Fine particles
3. About how many ozone monitoring sites are there in Mid-Atlantic states?
a) 5b) 20c) 50d) 100
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Further Learning & Additional Information
AirData, access to air pollution data, http://www.epa.gov/air/data/index.html List of Designated Reference and Equivalent Methods,
http://www.epa.gov/ttn/amtic/files/ambient/criteria/ref0506.pdf Continuous Emissions Monitoring Fact Sheet,
http://www.epa.gov/airmarkets/monitoring/factsheet.html Code of Federal Regulations, continuous emission monitoring guidelines, 40
CFR Part 75, http://www.access.gpo.gov/nara/cfr/waisidx_05/40cfr75_05.html A Guide to Mid-Atlantic Regional Air Quality, Part V: Measurements, Data
Analysis, and Modeling, pp. 59-66. http://www.marama.org/reports/Guide-MidAtlantic_RegAQ_Final.pdf