air quality monitoring

Air Quality Air Quality MonitoringMonitoring

ENV 4101/5105 Elements of Air Pollution

04/21/23 1Aerosol & Particulate Research Lab

http://www.statcan.ca/english/freepub/16-254-XIE/2007000/tablesgraphs/figure3-en.htm

Reading: Chap 7.1 & 7.2



Air Quality Monitoring Monitoring Considerations

• Manual vs. automated (real-time, continuous) monitoring• Sampling time• Federal reference method (FRM) vs. equivalent method (EM)

Monitoring of Ambient Air Pollutants• SO2, NOx, CO, O3

• Hydrocarbons• PM10, PM2.5

Source Sampling and Monitoring• Sampling train• Isokinetic sampling

Quality Assurance Programs• Quality Assurance• Quality Control

Air Quality Monitoring Network


What’s the use of ambient air quality monitoring data?

Monitoring Considerations

• Sampling location: limited number of fixed site monitors whose locations reflect objectives of air quality monitoring program

• Lower limit of detection (LOD): a sufficient amount of pollutant must be collected, f(sampling rate, duration)– Integrated sampling vs. real-time sampling– Area sampling vs. personal sampling

• Collection efficiency of the instrument:– Low flow rate for gas-phase contaminants (< 1 L/min)

04/21/23 Aerosol & Particulate Research Lab 3

Examples of criteria for selecting ambient sampling locations?

What are the objectives?

4

Differences in averaging times associated with real-time data

04/21/23 Aerosol & Particulate Research Lab

Which duration should you use?

5

National Ambient Air Quality StandardsPollutant Primary Stds. Averaging Times Secondary Stds.

CO 9 ppm (10 mg/m3) 8-hour(1) None

35 ppm (40 mg/m3) 1-hour(1) None

Pb 1.5 µg/m3 Quarterly Ave Same as Primary

NO2 0.053 ppm (100 µg/m3) Annual (Arith. Mean) Same as Primary

PM10 Revoked(2) Annual(2) (Arith. Mean)

150 µg/m3 24-hour(3)

PM2.5 15.0 µg/m3 Annual(4) (Arith. Mean) Same as Primary

35 µg/m3 24-hour(5)

O3 0.08 ppm 8-hour(6) Same as Primary

0.12 ppm 1-hour(7) (Applies only in limited areas)

Same as Primary

SO2 0.03 ppm Annual (Arith. Mean) -------

0.14 ppm 24-hour(1) -------

------- 3-hour(1) 0.5 ppm (1300 µg/m3)

http://www.epa.gov/air/criteria.html

04/21/23 Aerosol & Particulate Research Lab

Why different durations?

http://www.epa.gov/air/criteria.html#Air%20Quality%20Monitoring


http://www.epa.gov/air/criteria.html#Slide%202


http://www.epa.gov/air/criteria.html#Monitoring%20Considerations

http://www.epa.gov/air/criteria.html#Differences%20in%20averaging%20times%20associated%20with%20real-time%20data

http://www.epa.gov/air/criteria.html#National%20Ambient%20Air%20Quality%20Standards




Federal Reference Methods for Criteria Pollutants

Pollutant Reference Method

SO2Spectrophotometry (pararosanilne method)

NO2Gas-phase chemiluminescence

CO Nondispersive infrared photometry

O3Chemiluminescence

NMHCs Gas chromatography – FID (flame ionization detection)

PM10Performance-approved product

PM2.5Performance-approved product


SO2

FRM - Spectrophotometry (pararosanilne method)Air sample potassium tetrachloromercurate solution HgCl2SO3

-2 react with HCHO and colorless pararosaniline hydrochloride red-violet product measured spectrophotometrically SO2 concentration

EM – FT- IR Spectrometry (Absorption of IR by SO2 in the air SO2 concentration)


http://clu-in.org/programs/21m2/openpath/op-ftir/images/exhibit3.gif


SO2

EM – UV Fluorescence1) UV light excites SO2 to a higher energy state

SO2 + hv1 SO2*

2) Decay of the excited SO2*, emitting a characteristic radiation

SO2* SO2 + hv2

www.cse.polyu.edu.hk/~airlab/so2.jpg

NO – NO2 – NOx

FRM – Gas-Phase Chemiluminescence

Chemiluminescence: emission of light from electronically excited chemical species formed in chemical reactions.NO + O3 NO2* + O2

NO2* NO2 + hv

Measurement of NO2: conversion of NO2 to NO, and subsequent measurement by chemiluminescence.2NO2 + Mo 3 NO + MoO3

Possible interference: N-containing compounds higher measured NO2

Can you design an instrument that can measure the concentration of both NO and NO2 in the air?

www.k2bw.com/images/chem.gif


EM – FT- IR Spectrometry

CO

FRM – Nondispersive Infrared (NDIR) spectrometry

CO strongly absorbs infrared energy at certain wavelengths.

Detection device: two cylindrical cells, a sample and a reference cell. Difference in infrared energy in the two cells concentration of CO

SampleCell

ReferenceCell

CO

~ IR ~

Detection04/21/23 10Aerosol & Particulate Research Lab

O3

FRM – Chemiluminescence

Light emissions produced on reaction of O3 with ethylene (C2H4).

C2H4 flammable – replaced by Rhodamine B dye embedded in a disk

Rhodamine B does not attain a stable baseline rapidly after exposure to O3

EM – UV Photometry

Absorption of UV light (254 nm) by O3 and subsequent use of photometry to measure the reduction of UV energy

O3

UV light (254 nm) Detector

O3What would cause an interference on a UV photometry O3 monitor?


NMHCsFRM – Gas Chromatography - FID

Time

Inte

nsi

ty

Generate an electronic signal when a gas other than the carrier gas elutes from the column.

GC-Detector:

Stationary and mobile phases


NMHC• FID – Flame Ionization Detection:

– Combustion of organic substances– Positive ions (+) and electrons (-) are formed when

burned – change in current


http://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm

− Mass sensitive rather than concentration sensitive

Particulate Pollutants

http://www.recetox.muni.cz/images/airsag/PM10.jpg

PM10 sampler with size-selective inlet

• Impaction and filtration are the primary PM collection principles

• Measure the weight of exposed and clean filters

• High-volume sampler (Hi-Vol)• Typical sampling duration – 24 h

PM10 Sampler

• Remove particles > 10 µm by impaction on a greased surface

• Particles < 10 µm collected on a quartz glass fiber filter

What does the PM10 sampler measure? Number or mass concentration of particles?

Animation – PM10 Impactor


Dichotomous Sampler

http://crac.ucc.ie/images/sampler1.jpg

How can a Dichotomous sampler measure coarse (PM2.5-10) and fine (PM2.5) particles?

Animation – Virtual Impactor

TEOM Series 1400abAmbient Particulate MonitorThermo Electron Co.

Equivalent method: TEOM• Measure PM10, PM2.5, TSP• Tapered element oscillating

microbalance• Real-time measurement of

particle mass collected on a filter


Cascade ImpactorAnimation – Cascade Impactor

How can we collect different sizes of particles using cascade impactor?

Aerosol flow In

Clean air out


Source Sampling and Monitoring

Stack Sampling of PM1) Probe inserted into the stack2) Temperature sensor3) Pitot tube – gas velocity and flow rate4) Two-module sampling unit

Isokinetic Sampling1) Particles – inertial forces2) Samples must be collected at the

same rate of low as the stack gas


What’s the use of source emission data?

Isokinetic Sampling


Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001

Continuous Emission Monitoring (CEM)• Certain utilities and industrial sources are required

to measure stack emission continuously

• SO2, NO2, opacity, CO2, TRS, H2S, Hg


Opacity

Ringlemann chart

• Compare plume darkness to Ringlemann chart by trained smoke readers

• Averages of measurements of ¼ or ½ minute over an hour

• Simple, low cost, legal acceptance

Accuracy, Precision and Bias

Accuracy is a combination of random (precision) & systematic (bias) errors. Which of the 3 cases has the highest accuracy? Why?


100%

A

AOErRelative Error:

Coefficient of variation: 100% X

CV

Bias

Precision

Calibration

• Often used for adjusting bias-type errors• Measured values are compared to standard reference

values (for pollutant concentration) or standard airflow measuring techniques/devices (for volume air flow)

• Primary vs. secondary standard for flow: traceable to the National Institute of Standards and Technology (NIST)– Primary: bubble meter– Secondary: wet or dry test meters calibrated by bubble meter

• Gas standards: traceable to a NIST reference material– CO, SO2, NO2, NO: available in cylinder gas or permeation tubes

– O3: NIST certified O3 generator


Quality Assurance Programs

Quality Assurance (QA)• Setting policy and overseeing management controls• Planning, review of data collection activities and data use• Setting data quality objectives, assigning responsibilities,

conducting reviews, and implementing corrective actions

Goal: Valid and reliable air quality monitoring data

Quality Control (QC)• Technical aspects of data quality programs• Implementation of specific QC procedures:

calibrations, checks, replicate samples, routine self-assessment, and audits

It is federal rule to document QA/QC efforts !


Air Quality Monitoring NetworkState and Local Air Monitoring Stations (SLAMS)

• Highest pollutant concentrations• Representative concentrations in areas of high population density• Impact of major emission sources• Regional background concentrations• Extent of pollutant transport among populated areas• Welfare-related impacts in more rural and remote areas

National Air Monitoring Stations (NAMS) • Urban area, long-term air quality monitoring network• Air quality comparisons and trends analysis

Photochemical Assessment Monitoring Stations (PAMS) • Monitor O3 and photochemical air pollutants

Clean Air Status and Trends Network (CASTNet)• Primary source for rural O3 level and dry atmospheric deposition


National Atmospheric Deposition Program (NADP)• Assess the problem of atmospheric deposition and its effects on aquatic

and terrestrial ecosystems (H+, NH4+, SO4

2-, NO3-, Cl-, Ca2+, Mg2+, K+, Hg)

Quick Reflections Monitoring Considerations

• Manual vs. automated (real-time, continuous) monitoring• Sampling time• Federal reference method (FRM) vs. equivalent method

(EM) Monitoring of Air Pollutants

• SO2, NOx, CO, O3

• Hydrocarbons• PM10, PM2.5

Source Sampling and Monitoring• Sampling train• Isokinetic sampling

Quality Assurance Programs• Quality Assurance• Quality Control

Air Quality Monitoring Network


air quality monitoring

Documents

air so2 concentration

excited so2

air quality monitoringenv

characteristic radiation

ppm annual arith

ambient sampling locations

elements of air pollution

realtime data