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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