4101/5105 ENV Elements of Air Pollution
Reading: Chap 7.1 & 7.2
Air Quality Monitoring
http://www.statcan.ca/english/freepub/16-254-XIE/2
08/06/09
Aerosol & Particulate Research Lab
1
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?
08/06/09 Aerosol & Particulate Research Lab 2
Monitoring Considerations
Sampling location: limited number of fixed site monitors whose locations reflect objectives of air quality monitoring program
What are the objectives? Examples of criteria for selecting ambient sampling locations?
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)
08/06/09 Aerosol & Particulate Research Lab 3
Differences in averaging times associated with real-time data
Which duration should you use?
08/06/09 Aerosol & Particulate Research Lab 4
National Ambient Air Quality Standards
Pollutant CO Primary Stds. 9 ppm (10 mg/m3) 35 ppm (40 mg/m3) Pb NO2 PM10 PM2.5 O3 1.5 g/m3 0.053 ppm (100 g/m3) Revoked(2) 150 g/m3 15.0 g/m3 35 g/m3 0.08 ppm 0.12 ppm SO2 0.03 ppm 0.14 ppm ------Averaging Times 8-hour(1) 1-hour(1) Quarterly Ave Annual (Arith. Mean) Annual(2) (Arith. Mean) 24-hour(3) Annual(4) (Arith. Mean) 24-hour(5) 8-hour(6) 1-hour(7) (Applies only in limited areas) Annual (Arith. Mean) 24-hour(1) 3-hour(1) Same as Primary Same as Primary ------------0.5 ppm (1300 g/m3)
http://www.epa.gov/air/criteria.html
Secondary Stds. None None Same as Primary Same as Primary
Same as Primary
Why different durations?
08/06/09 Aerosol & Particulate Research Lab
5
Federal Reference Methods for Criteria Pollutants Pollutant SO2 NO2 CO O3 NMHCs PM10 PM2.5 Reference Method
Spectrophotometry (pararosanilne method) Gas-phase chemiluminescence Nondispersive infrared photometry Chemiluminescence Gas chromatography FID (flame ionization detection) Performance-approved product Performance-approved product
08/06/09
Aerosol & Particulate Research Lab
6
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
08/06/09
Aerosol & Particulate Research Lab
7
SO2
EM UV Fluorescence
1) 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 08/06/09 Aerosol & Particulate Research Lab 8
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
EM FT- IR Spectrometry
www.k2bw.com/images/chem.gif
Can you design an instrument that can measure the
2
08/06/09
Aerosol & Particulate Research Lab
9
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
CO
Sample Cell
~ IR ~
Reference Cell
08/06/09
Detection
Aerosol & Particulate Research Lab
10
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 O3
08/06/09
What would cause an interference on a UV
3
Aerosol & Particulate Research Lab
11
NMHCs
FRM Gas Chromatography - FID
Intensity
Time
Stationary and mobile phases
GC-Detector:
Generate an electronic signal when a gas other than the carrier gas elutes from the column.
08/06/09
Aerosol & Particulate Research Lab
12
NMHC
FID Flame Ionization Detection:
Combustion of organic substances Positive ions (+) and electrons (-) are formed when burned change in current - Mass sensitive rather than concentration sensitive
http://teaching.shu.ac.uk/hwb/chemistry/tutorials/chrom/gaschrm.htm
08/06/09
Aerosol Particulate & Research Lab
13
Particulate Pollutants
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 Animation PM 10 Impactor PM10 Sampler Remove particles > 10 m by impaction on a greased surface Particles < 10 m collected on a quartz glass fiber filter
10
PM10 sampler with size-selective inlet
http://www.recetox.muni.cz/images/airsag/PM10.jpg 08/06/09
What does the PM sampler measure? Number or mass concentration of particles? Aerosol & Particulate Research Lab
14
Dichotomous Sampler
Animation Virtual Impactor
TEOM Series 1400ab Ambient Particulate Monitor Thermo Electron Co.
http://crac.ucc.ie/images/sampler1.jpg
How can a Dichotomous sampler
2.5-10
measure coarse (PM
2.5
) and fine
Equivalent method: TEOM Measure PM10, PM2.5, TSP Tapered element oscillating microbalance Real-time measurement of particle mass collected on a filter
08/06/09
Aerosol & Particulate Research Lab
15
Animation Cascade Impactor
Cascade Impactor
Aerosol flow In
Clean air out
08/06/09
Aerosol & Particulate Research Lab
How can we collect different sizes of particles using cascade impactor?
16
Source Sampling and Monitoring
Stack Sampling of PM 1) Probe inserted into the stack 2) Temperature sensor 3) Pitot tube gas velocity and flow rate 4) Two-module sampling unit
Isokinetic Sampling 1) Particles inertial forces 2) Samples must be collected at the same rate of low as the stack gas
What's the use of source emission data?
08/06/09 Aerosol & Particulate Research Lab 17
Isokinetic Sampling
Fig 8 -2, Aerosol Measurement, 2nd Edition, 2001
08/06/09
Aerosol & Particulate Research Lab
18
Continuous Emission Monitoring (CEM)
Certain utilities and industrial sources are required to measure stack emission continuously SO2, NO2, opacity, CO2, TRS, H2S, Hg
Opacity
Compare plume darkness to Ringlemann chart by trained smoke readers Averages of measurements of or minute over an hour Simple, low cost, legal acceptance
Ringlemann chart
08/06/09 Aerosol & Particulate Research Lab 19
Accuracy, Precision and Bias
Relative Error:
Er ( % ) = O- A 100 A
Bias Precision
Coefficient of variation: CV ( % ) =
100 X
Accuracy is a combination of random (precision) & systematic (bias) errors. Which of the 3 cases has the highest accuracy? Why?
08/06/09 Aerosol & Particulate Research Lab 20
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
08/06/09
Aerosol & Particulate Research Lab
21
Quality Assurance Programs
Goal: Valid and reliable air quality monitoring data 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 Quality Control (QC) Technical aspects of data quality programs Implementation of specific QC procedures: calibrations, checks, replicate samples, routine selfassessment, and audits It is federal rule to document QA/QC efforts !
08/06/09
Aerosol & Particulate Research Lab
22
Air Quality Monitoring Network
State 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+, SO42-, NO3-, Cl-, Ca2+, Mg2+, K+, Hg)
08/06/09 Aerosol & Particulate Research Lab 23
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
08/06/09 Aerosol & Particulate Research Lab 24