Atmospheric Aerosol From the Source to the Receptor Insights from the Pittsburgh Supersite

1
Atmospheric Aerosol From the Source to the
Receptor Insights from the Pittsburgh Supersite

• Spyros Pandis, Allen Robinson, and Cliff Davidson
• Department of Engineering and Public Policy
• Carnegie Mellon University

2
Aerosol Size Distribution
3
Air Pollution in Pittsburgh
USX Tower
July 2, 2001
PM2.54 mg m-3
July 18, 2001
PM2.545 mg m-3
4
FRM PM2.5 Concentrations During PAQS
PM2.5 (µg/m3)
2001 2002
5
Fine PM Composition
PM2.5 mass
PM2.5 (mg/m3)
Jul Aug Sep Oct Nov Dec
Jan Feb Mar Apr May Jun

2001 2002

6
PM2.5 Mass Balance (July and August 2001)
Crustal
EC
Ammonium
Nitrate
Sulfate
PM2.5 (µg/m3)
Organics
1 8 15 22 29 5
12 19 26
July
August
7
Mass Balance Closure July 2001
Water
Crustal
NO3
SO4
NH4
EC
60
OC1.8
FRM
50
40
PM2.5 (mg m-3)
30
20
10
0
1 4 7 10 13
16 19 22 25 28
31
Date (July 2001)
Good mass balance was achieved for the winter
months
8
Satellite Sites Outside Pittsburgh
Steubenville
Greensburg
Holbrook
Athens
9
Sulfate Mass at Main Site and Satellite Sites
10
Continuous Sulfate Measurements and Long Range
Transport
000 EST 1200 EST

• July 26, 2002
• (16.2 mg m-3)
• Increase as winds shift direction
• Decrease after a front passed, wind
  speeds decreased, and some rain fell

PM2.5 Sulfate (mg/m3)
2400
Hour (EST)
11
The Source-Receptor Challenge Interactions
between Fine PM and Their Precursors
Crustal
Primary Inorganic PM emissions
Ammonium
EC
NH3 emissions
Primary Organic emissions
Organics
VOC emissions
Sulfate
SO2 emissions
Nitrate
NOx emissions
PM2.5 Composition during the Winter
12
Ammonium Nitrate Formation

• The formation of ammonium nitrate requires
• Nitric acid (major sources of NOx in the US are
  transportation and power plants)
• Free ammonia (ammonia not taken up by sulfate)
• The formation reaction is favored at
• Low temperatures (night, winter, fall, spring)
• High relative humidity
• Hypothesis A significant fraction of the sulfate
  reduced will be replaced by nitrate when SO2
  emissions are reduced.

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Modeling Nitrate Partitioning
Summer
Aerosol Nitrate (mg m-3)
Winter
Date
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Effect of Sulfate Concentration Changes on
Inorganic PM2.5
Inorganic PM2.5 (mg m-3)
Sulfate Reduction
15
Reductions of Sulfuric and Nitric Acid
(Pittsburgh, July 2001)
3
0
2
0
Inorganic PM2.5 Reduction ()
-50 Nitric Acid
1
0
Same Nitric Acid
0
0
1
0
2
0
3
0
Sulfate Reduction ()
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Reductions in Ammonia(July 2001)
20 Sulfate Reduction
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Reducing Inorganic PM2.5

• Using an observation-based model
• Controls of SO2 will reduce sulfate and PM2.5 in
  all seasons.
• A fraction of the now existing sulfate will be
  replaced by nitrate.
• The lifetime of nitrate will increase during the
  summer because it will move from the gas to the
  aerosol phase
• For Pittsburgh, ammonia controls in all seasons
  can minimize the replacement of sulfate by
  nitrate.
• For Pittsburgh, NOx controls will help reduce the
  nitrate during the winter but they will have a
  small effect during the summer.

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Source Apportionment of Organic Aerosol
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OC and EC Measurements
OC and EC (mg C/m3)
July
August

• Use of 3 samplers (TQQQ, denuder-based,
  semi-continuous)
• Five sets of measurements for EC-OC

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Ozone as indicator of SOA Production
Ozone
OC/EC Ratio
O3 (ppb)
OC/EC Ratio (front quartz)
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Daily Averaged OC Composition (July 2001)
Secondary
Primary
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Monthly Average SOA
50
40
30
SOA ( OC)
20
10
0
Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr
May Jun Jul
2002
2001
23
Primary Biogenic Contribution
24
(No Transcript)
25
Fence Line Sampling to Characterize Emissions
from Coke Facility
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Fingerprinting a Coke Processing Plant
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Looking at Single Particles from the Coke Facility
Single Particle Mass Spectrometry (Wexler, UC
Davis)
C3H8N
C
C5H12N
NH
C4H10N
C2H6N
Alkyl Amines (81 of particles)
CH4N
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Iron and Cerium Class from Steel Facility
N
Fe
Ce
CeO
CeO2
FeO, Ce2
140o
Wind Direction
29
Typical PM Size Distribution EvolutionAugust 10,
2001
30
Nucleation and Growth a Few Hours After Sunrise
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Nucleation and Visibility
USX Tower
USX Tower
32
Nucleation Frequency
Fraction of Days With Nucleation
2001
2002

• Significant fraction of days (30)
• Most prevalent in spring, fall

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Aerosol Number and Mass
20x104
Pittsburgh, PA 2001-2002
10x104
Number (/cm3)
Aerosol Mass (µg/m3)
PM2.5 (mg m-3)

• Negative correlation related to nucleation
  activity

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Composition of 10-60 nm Particles(Jimenez, U.
Colorado and Worsnop, Aerodyne)
Mass Fraction (10-60 nm Particles) Aerosol Mass
Spectrometer
Nitrate
100
Ammonium
Sulfate
Mass Fraction 10-60 nm
Organics
50
0
500
100
Particle Size (nm)
10
0000
0600
1200
1800
2400
Zhang Jimenez (Univ. Colorado-Boulder)
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Nucleation Model Evaluation (July 27, 2001)
Measured
Predicted
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Nucleation and Ultrafine Particles

• The model was successful in reproducing the
  observed behavior (nucleation or lack of) in all
  simulated dates in July (10) and January (10)
• Strong evidence that the nuclei are sulfuric
  acid/ammonium/water clusters
• Growth with the help of organics
• Discrepancies in the nucleation rates
• the model tends to predict higher rates
• Ammonia appears to be the controlling reactant !
• Small to modest reductions of ammonia can turn
  off the nucleation in the area especially during
  the summer

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PMCAMx Modeling Domain
PM2.5 Sulfate

• 36x36 km grid, 14 levels up to 6 km
• 10 aerosol sections, 13 aerosol species
• 20 million differential equations
• 8 CPU hours on a PC per simulation day
  (EQUIlibrium module)

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PM2.5 Sulfate Simulation (July 2001)
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SOA Simulation (July 2001)
Anthropogenic
Biogenic
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PMCAMx Evaluation in Pittsburgh
PM2.5
Nitrate
Sulfate
Ammonium
OM
EC
41
Predicted vs. Estimated in Pittsburgh (Primary
and Secondary OA)
Predicted ?g/m3
Estimated ?g/m3
EC Tracer Method (Cabada et al., 2003)
42
PM2.5 Response () to 30 SO2 Emission Reduction

July 18, 2001
Concentration Change (mg m-3)
Percent Change
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Conclusions

• Water is retained in the FRM filters during the
  days with high sulfate and acidity
• The water can be estimated with a thermodynamic
  model and it will decrease as sulfate decreases
• Large regional contributions for both sulfate and
  organics
• Development of observation based model for the
  substitution of sulfate by nitrate (requires
  nitric acid and ammonia measurements)
• SO2 reductions will reduce sulfate and PM2.5 but
  nitrate will also increase in all seasons
• Ammonia reductions can prevent the nitrate
  increase
• NOx reductions can help during the winter
• Organic aerosol sources
• Roughly 30-40 of the organic PM is secondary
  during the summer (higher in worst days) and
  around 10 during the winter.
• Evidence for significant primary biogenic PM
  during the summer (around 30)
• Transportation and biomass burning are the other
  significant sources in the area

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Conclusions (continued)

• New technologies (Single Particle Mass
  Spectrometry, semi-continuous metal measurements)
  allow the fingerprinting of point sources.
• Frequent nucleation events (around 100 per year)
• At low PM concentrations
• Sunlight
• Evidence for regional scale (100-300 km)
• Sulfuric acid/ammonia/water nuclei
• Ammonia appears to be the limiting reactant for
  most events
• Supersite data together with the results from
  other studies and networks will allow us to
  evaluate our understanding of atmospheric PM in
  the US
• First results of PMCAMx for summer 2001 are
  encouraging
• Consistency between 3D CTM results and
  observation based models for nitrate and SOA.