eas 4/8803: experimental methods in aq
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March 24, 2004 EAS 4/8803 1
EAS 4/8803: Experimental Methods in AQ
Week 11:
Air Quality Management (AQM)Clean Air Act (History, Objectives, NAAQS)
Emissions and Atmospheric Trends (Links)
Principal Measurement Techniques (NOx, CO, SO2)
Measurement of CO (Exp 5)NDIR Method (Interferences, Stability, DL, Precision, Accuracy)
Controlling O3 and PM2.5
Principal Measurement Techniques (O3, PM2.5)
Atmospheric Transport & Photochemistry (NOx vs VOC, SOA)
Ambient Measurements and Trends (World, USA, GA)
Measurement of O3 (Exp 6)
UV Absorption (Interferences, Stability, DL, Precision, Accuracy)
March 24, 2004 EAS 4/8803 2
Tapered Element Oscillating Microbalance
If PM of mass m deposit on piezoelectric quartz crystal, frequency changes by
f = Kq Q t cm
with sensitivity Kq, aerosol mass flow Q,
time t, and PM mass concentration cm
March 24, 2004 EAS 4/8803 3
TEOM Method
If PM of mass m deposit on piezoelectric quartz crystal, frequency changes by
f = Kq Q t cm
with sensitivity Kq, aerosol mass flow Q,
time t, and PM mass concentration cm
March 24, 2004 EAS 4/8803 4
TEOM Setup and Operation
Reducing H2O Interference
• Inclusion of Nafion dryer using
TEOM’s exhaust (low p, dry)
as sheath flow.
• Filter housing T-controlled
at 50 oC.
March 24, 2004 EAS 4/8803 5
Assessing Accuracy of PM2.5 Mass Measurements
Comparison of dry TEOM averages with dehydrated Teflon samples
Williams Tower is ~20 km west of LaPorte, which is close to Ship Channel
70
60
50
40
30
20
10
0
30 m
in T
EO
M (
ug
m-3
)
403020100
discrete PCM (ug m-3
)
Will. TowerMass r = 0.92slope = 0.96 +-0.07i-cept = 2.52 +-1.23
70
60
50
40
30
20
10
0
30 m
in T
EO
M (
ug
m-3
)403020100
discrete PCM (ug m-3
)
LaPorteMass r = 0.95slope = 1.01 +-0.05i-cept = 0.98 +-0.81
excl 1st 3 PCM
254 m agl 6 m agl
March 24, 2004 EAS 4/8803 6
High Resolution vs Integrated [PM2.5]at LaPorte and Williams Tower
60
40
20
0
μg
m-3
PM2.5 Mass PCM LP WT TEOM LP WT
Large [PM2.5] transients (spikes) at both sites: Chemistry or transport?
Transients (changes in [PM2.5]) larger at WT, esp. at night.
Averages of integrated samplers (8-24h) are very similar and follow a regional trend.
March 24, 2004 EAS 4/8803 7
Adding Photochemistry (O3)
60
40
20
0
μg
m-3
PM2.5 Mass PCM LP WT TEOM LP WT
200
150
100
50
0
pp
bv
O3 LP WT
NOy(LP)
80
60
40
20
0
-20
ne
m-3
8/29/2000 8/31/2000 9/2/2000 9/4/2000 9/6/2000 9/8/2000Date (CST)
PM2.5 Acidity (SO4=/NO3
-/NH4
+) LP WT
LP max [O3] on 08/30 is more than twice WT-[O3], which seems to follow a “rising tide”.
Fast P(O3) at LP (<200 ppb/h): high precursor emissions (Alkenes, NOx) in Ship Channel.
More regional influence from BB plume on 9/5 + 9/6: joint increase in [PM2.5].
March 24, 2004 EAS 4/8803 8
Average Diurnal Differences in [O3] and [PM2.5]
100
80
60
40
20
0
Ozo
ne
(p
pb
v)
00:00 06:00 12:00 18:00 00:00
LaPorteWill.Tower
WT-O3 levels are significantly higher at night and early mornings: Separation from nocturnal surface inversion; LP-O3 titration.LP-O3 higher at midday: >P(O3) from precursor mix and closer sources.
-30
-20
-10
0
10
20
Ozo
ne
WT-
LP
(
pp
bv
)
00:00 06:00 12:00 18:00 00:00
Δ-O3
center 67 %
30
25
20
15
10
5
TE
OM
mas
s
(µg
m-3
)
00:00 06:00 12:00 18:00 00:00Time (CST)
LaPorteWill.Tower
10
5
0
-5
-10
PM
WT-
LP
(
µg
m-3
)
00:00 06:00 12:00 18:00 00:00Time (CST)
Δ-PM2.5
center 67 %
Trend to higher WT-[PM2.5] mostly at night, similar to vertical gradients at Hendersonville, but note 20 km WT-LP distance!
March 24, 2004 EAS 4/8803 9
Vertical Gradients of PM2.5
Direct emissions and/or secondary formation of fine PM aloft.
Free Troposphere Source for PM2.5!
During SOS’99, 16 June - 22 July 1999,
measurements near Nashville, TN,
between 4 and 42 m agl showed
positive vertical gradients for
60-70 % of all daytime, and
70-80 % of all nighttime samples of
PM2.5 mass, SO4=, NO3
-, and NH4+!!
March 24, 2004 EAS 4/8803 10
Vertical Gradients of PM2.5
Free Troposphere Source for PM2.5!
BL Dynamics Important Influence on Ground-Based AQ Monitoring !!
12
10
8
6
4
2
0
-2
C
42m
-4m
(
g m
-3)
Daytime MASS SO4 NO3 NH4Nighttime MASS SO4 NO3 NH4
-6
-4
-2
0
2
4
WS
, T, R
H 4
2m-4
m
6/21/99 6/26/99 7/1/99 7/6/99 7/11/99 7/16/99 7/21/99Time (EST)
Daytime WS T RHNighttime WS T RH
March 24, 2004 EAS 4/8803 11
Vertical Wind Profile: Advection Horizontal Transport
Near logarithmic increase of WS and uniform WD within well-mixed BL.
Clockwise rotation with height near BL top to merge with more geostrophic winds.
Nighttime separation of layers with different wind speeds and directions.
March 24, 2004 EAS 4/8803 12
PM2.5 Wind Roses: Seasonal Differences Across GAIndications for Regional Advective Transport?
Period 2001+ 02MAY-OCT NOV-APR
34.4
34.2
34.0
33.8
33.6
33.4
33.2
33.0
32.8
32.6
32.4
32.2
32.0
-85.5 -85.0 -84.5 -84.0 -83.5 -83.0 -82.5 -82.0
Atlanta
FAQS measurement sites GA-EPD monitoring sites coal burning power plants point sources w/ CO:NOx > 1
20x20 km
N
E
S
W9 18
µg m-3
15.813.4Griffin
N
E
S
W9 18
µg m-3
16.715.5Macon SBP
N
E
S
W9 18
µg m-3
Columbus OLC 16.6 19.3
N
E
S
W9 18
µg m-3
15.014.2Augusta RP
N
E
S
W18 36
µg m-3
36.8
Aug’99
March 24, 2004 EAS 4/8803 13
…Similarity to Daytime O3
Period 2001+ 02MAY-OCT NOV-APR
34.4
34.2
34.0
33.8
33.6
33.4
33.2
33.0
32.8
32.6
32.4
32.2
32.0
-85.5 -85.0 -84.5 -84.0 -83.5 -83.0 -82.5 -82.0
Atlanta
FAQS measurement sites GA-EPD monitoring sites coal burning power plants point sources w/ CO:NOx > 1
20x20 km
N
E
S
W30 60
ppb
38.228.5Macon SBP
N
E
S
W30 60
ppb
Columbus OLC 30.7 19.8
N
E
S
W30 60
ppb
30.222.2Augusta RP
N
E
S
W30 60
ppb
44.236.1Griffin
N
E
S
W60 120
ppb
106
Aug’99
March 24, 2004 EAS 4/8803 14
Summertime PM2.5 – Max(O3) Relationship
Tighter correlation in July 2001.
“Downwind” Griffin site offset to higher PM2.5 mass.
August 99 in Atlanta was hotter, dryer, more polluted with O3-precursor species.
March 24, 2004 EAS 4/8803 15
Seasonal & Regional Comparison of PM2.5 Composition
Summer Months
Regional Difference: Higher OM/OC and OC/EC at more rural site!Seasonal Difference: Lower OM/OC and (higher) OC/EC in winter.
More SOA in August 99? More oxygenated POCs away from Atlanta?
Winter Months
March 24, 2004 EAS 4/8803 16
Atlanta JST Griffindownwind
120
100
80
60
40
20
0
O3
(
pp
bv
)
35302520151050
NOz (ppbv)
July 2001Sunny daytimesNortherly flowslope = 13.7 +-0.59intcept= 34 +-1.5r = 0.86incl "lost" HNO3
slope = 2.9 +-0.21intcept= 34 +-2.4r = 0.72
120
100
80
60
40
20
0
O3
(
pp
bv
)
35302520151050
NOz (ppbv)
Sunny daytimesAugust 1999slope = 3.6 +-0.14intcept= 59 +-1.5r = 0.59July 2001slope = 2.7 +-0.28intcept= 38 +-2.7r = 0.50December 2001slope = -0.6 +-0.09intcept= 33 +-1.1r = -0.42
Elevated regional O3 background reflected in regression’s intercept: higher in Aug 99!
At JST higher intercept and slope during Aug ’99 (OPE= 4 vs 3): more efficient P(O3).
OPE in air mass arriving at Griffin is likely larger given by upper and lower limits.
Lower limit assumes 1st order loss of HNO3 due to surface deposition at k ≈ 0.22 h-1.
Air mass transitions from VOC-limited to NOx-limited regime due to Biogenic HC.
High photochemical activity P(O3) allows for high P(SOA): rural/urban gradient.
Photochemical ActivitySource – Receptor Considerations: O3/NOz as “OPE”
March 24, 2004 EAS 4/8803 17
Photochemical Processes Leading to O3 and PM
SOA
NOz
An Assessment of Tropospheric Ozone Pollution, A North American Perspective, NARSTO, National Acad. Press, 2000.
March 24, 2004 EAS 4/8803 18
Ozone Isopleths
Area of effective VOC control (most often highly populated areas)
Volatile Organic Compounds (VOC)
Nit
rog
en O
xid
es
(NO
x) Constant [O3]
Low [O3]
High [O3]
NOx control effective(areas with high biogenics)
March 24, 2004 EAS 4/8803 19
SOA & O3 Formationand Transport
PM, SO2, NOx
Emissions
VOCEmissions
Wind
DepositionRainout
O3, HNO3
PM
NO
hv
RO2 /HO2 RO,OH
NO2
O2
O3
HNO3
OH
OH
Fine PM, SOA
March 24, 2004 EAS 4/8803 20
Planetary Boundary Layer Dynamics
Comparison of PBL and Free Troposphere Characteristics
Property PBL FT
Turbulence Near continuous over Zi. Convective clouds; sporadic
in thin layers extending horizontally.
Friction Large drag & energy dissipation. Small viscous dissipation.
Dispersion Rapid in vertical & horizontal. Small molecular diffusion; rapid
horizontally by mean wind.
Winds WS log profile in surface layer. Nearly geostrophic.
Vertical Transport Mainly turbulence. Mean wind, cumulus-scale.
Thickness 100 – 3000 m, f (time/space). 8 – 18 km, less variable.
Diurnal oscillations over land. Slow time variations.
PBL strongly influenced by Earth’s surface, responding to surface forcings within 30-60 min
March 24, 2004 EAS 4/8803 21
Turbulence in PBL
Assuming an air parcel rises or sinks adiabatically, i.e. no energy is supplied nor removed, it expands and cools as it reaches lower ambient pressure aloft, or compresses and warms as it reaches higher pressure below. If the ambient vertical temperature profile (lapse rate) is less steep, the air parcel will continue to rise or fall once in (vertical) motion.
Superadiabatic T profile (unstable layer)
March 24, 2004 EAS 4/8803 22
Consequences for Dispersion/Dilution
Weakly instable to neutral layer: Dispersion driven by advection (horizontal WS).
Highly instable layer: Dispersion driven by thermal looping (vertical & horizontal).
March 24, 2004 EAS 4/8803 23
Effects of Terrain (Friction)
March 24, 2004 EAS 4/8803 24
Temperature Inversion
Assuming an air parcel rises or sinks adiabatically, i.e. no energy is supplied nor removed, it expands and cools as it reaches lower ambient pressure aloft, or compresses and warms as it reaches higher pressure below. If the ambient vertical temperature profile (lapse rate) is steeper, the air parcel will return to its original position.
Subadiabatic T profile (stable layer)
March 24, 2004 EAS 4/8803 25
Inversion Types and Formation
Elevated
Surface
Subsidence inversion: Large scale sinking of cold (but warming) air meets rising cooling air (thermals) under regional high pressure conditions.Frontal inversion: Warm moist air from S glides over cold dry air from N.
Radiational inversion: Radiative heat loss at night from the Earth’s ground into space according to Tg
4.
March 24, 2004 EAS 4/8803 26
Typical PBL Evolution in Summer
Stull, R. B., 1988: An Introduction to Boundary Layer Meteorology. Kluwer Academic, 666 pp.
March 24, 2004 EAS 4/8803 27
Potential Temperature () Profiles…is T an air parcel at P and T would have if it were at Ps (conserved for adiabatic motions, i.e., d/dt = 0).
Afternoon After sunset Before sunrise After sunrise Before noon Noon
March 24, 2004 EAS 4/8803 28
PBL Winter vs Summer
March 24, 2004 EAS 4/8803 29
00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00
Time (EST)
WINTER HALF NOV-APRMac '01/'02 '00/'01Col '01/'02 '00/'01Aug '01/'02 '00/'01
25
20
15
10
5
0
PM
2.5
(
g m
-3)
00:00 03:00 06:00 09:00 12:00 15:00 18:00 21:00 00:00
Time (EST)
SUMMER HALF MAY-OCTGrif '02Mac '02 '01 '00Col '02 '01 '00Aug '02 '01 '00
Seasonal Differences in Diurnal Cycles of PM2.5
Midday minimum due to BL mixing seems compensated by SOA in summer.
PM2.5 sources near Columbus drive nighttime averages in winter 2001/02.
Summer stagnation with high O3 also leads to high PM2.5 (e.g. 2000).
Annual PM2.5 NAAQS (15 g m-3) sensitive to:
- SOA formed under regional stagnation in summer;
- Primary PM2.5 from local sources at night in winter.
WinterSummer
March 24, 2004 EAS 4/8803 30
30
20
10
0WS
(m
/s)
Tm
ax-
Tm
in(C
)
3000
2000
1000
0
BL
H-d
ay
(m)
1000
800
600
400
200
0
Ft B
ac
r bu
rne
d B
LH
-nig
ht (m
)
10/17/01 10/21/01 10/25/01 10/29/01 11/2/01 11/6/01 11/10/01 11/14/01 11/18/01 11/22/01 11/26/01
Time (EST)
4
68
10
2
4
68
100
2
4
24
h -
PM
2.5
(
µg
m-3
)
Columbus OLCGriffin Macon Augusta
wild firesprescribed
-10
0
10
Win
d B
arb
PM2.5 Exceedances at Columbus in Oct-Nov 2001
March 24, 2004 EAS 4/8803 31
PM2.5 at Columbus in Oct-Dec 2001
2.52.01.51.00.5
24h - WS (m s-1
)
448
142
600500400300200100GFC-BLHnight (m agl)
448142
300020001000GFC-BLHday (m agl)
448142
10008006004002000
FtB total acr burned
448142
80
60
40
20
0
24h
- P
M2
.5
(µg
m-3
)
2015105Tmax- Tmin (K)
448
142
Critical parameters driving [PM2.5]:
• size of burn, distance and plume trajectory
• atmospheric divergence (horizontal wind speed)
• {vertical} boundary layer stability (T difference)
• BL mixing depth at night (BLHnight)
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