Continuous measurement of
airborne particles and gases
Jeff Collett and Taehyoung Lee
Atmospheric Science Department
Colorado State University
Funding: USDA/AES and NPS
Outline
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Why measure particles and gases at high
time resolution?
Examples of previous applications
Measurement approach
Initial results
Summary and future research plans
Emissions, transport and
deposition of pollutants


Atmospheric particles can be emitted directly or produced by
reactions in the atmosphere
Adverse impacts (health, visibility, ecosystem) occur on local to
regional scales
Aneja et al. (2006)
Particle
composition

Many particles in
polluted
atmospheres are
combinations of
ammonium with
sulfate and/or
nitrate
Northern Front Range Air Quality Study – 1997 Winter
Particle formation

Gaseous sulfur dioxide reacts to
form particulate sulfuric acid/sulfate
H2SO4(p) + 2NH3(g)  (NH4)2SO4(p)

Gaseous nitrogen oxides react to
form gaseous nitric acid
HNO3(g) + NH3(g) NH4NO3(p)

Particulate ammonium nitrate
generally forms only when
ammonia > sulfate
Data from the IMPROVE program
http://vista.cira.colostate.edu/improve/Default.htm
Why measure
particles + gases?

Particles are regulated
–
–
Regional haze rule
Health-based NAAQS
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Gases are precursors
to particle formation
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Partitioning between
gases and particles
changes over time
Contrasting afternoon visibilities at
Great Sand Dunes NP
Why measure at high time resolution?
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Source
characterization
–
–
–
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Emission rates
change
Upwind composition
may change
Wind direction
changes source
influence
Ambient air quality
–
–
Pollutant transport
changes
“Tracking” between
species helps us
understand
composition
Example 1. changes in aerosol composition at
an agricultural site in Illinois
36
NH4+_ug/m3
NO3-_ug/m3
SO4=_ug/m3
31
Nitrate and sulfate both important

21
–
–
16
Acidic sulfate aerosol at times
NH4NO3 and (NH4)2SO4 at times
11
6
Date
2/23/2003
2/22/2003
2/21/2003
2/20/2003
2/19/2003
2/18/2003
2/17/2003
2/16/2003
2/15/2003
2/14/2003
2/13/2003
2/12/2003
2/11/2003
2/10/2003
2/9/2003
2/8/2003
2/7/2003
2/6/2003
2/5/2003
2/4/2003
2/3/2003
1
2/2/2003
Concentration, ug/m3
26
Example 2. Southern California
mountain wilderness area
700
NH4+, neq/m3
NO3-, neq/m3
SO4=, neq/m3
NH4NO3 particles dominate
Large daily variability tied to mountain-valley winds

500

400
300
200
4/27
4/26
4/25
4/24
4/23
4/22
4/21
4/20
4/19
4/18
4/17
4/16
4/15
4/14
4/13
4/12
4/11
4/10
4/9
4/8
4/7
4/6
0
4/5
100
4/4
Concentration, neq/m3
600
Example 3. Yosemite National Park
Note “tracking” of sodium and nitrate
Nitrate replaced chloride in sea salt
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
HNO3(g) + NaCl(p)  NaNO3(p) + HCl(g)
30
25
Cl-
NO3-
Na+
neq/m3
20
15
10
5
0
8/12
8/13
8/14
8/15
8/16
8/17
8/18
8/19
8/20
8/21
8/22
8/23
8/24
8/25
8/26
8/27
Particle nitrate
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Fine (submicron) ammonium nitrate particles
–
–
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Coarse (supermicron) reacted sea salt or soil dust particles
–
–
–
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Favored at low T, high RH, high NH3
HNO3(g) + NH3(g) NH4NO3(p)
More likely at high T and low NH3
HNO3(g) + NaCl(p)  NaNO3(p) + HCl(g)
2 HNO3(g) + CaCO3(p)  Ca(NO3)2(p) + CO2 + H2O
Lesson: careful characterization of ammonia availability and
chemical speciation of particle nitrate key to understanding
impacts of agricultural ammonia on regional particle formation
Particle nitrate speciation
Ca(NO3)2
16%
NaNO3
4%
NH4NO3
80%
NH4NO3
25%
Ca(NO3)2
7%
Ca(NO3)2
35%
NH4NO3
49%
Bondville (Feb), f (T, RH)
Ca(NO3)2
6%
NaNO3
40%
NaNO3
44%
summer
Grand Canyon (May), f (T, RH, Soil)
Yosemite (Aug), f (T, RH, Sea salt)
Ca(NO3)2
7%
NaNO3
9%
Ca(NO3)2
15%
NH4NO3
36%
NaNO3
39%
NH4NO3
1%
NH4NO3
55%
Brigantine (Nov), f (T, RH, Sea salt)
NH4NO3
5%
Ca(NO3)2
26%
Ca(NO3)2
NH4NO3
NaNO3
84%
49%
NaNO3
73%
San Gorgonio (April), f (T, RH, Sea salt)
summer
San Gorgonio (July), f (T, RH, Sea salt)
41%
NaNO3
54%
summer
Big Bend (July - Oct), f (T, RH, Sea salt)
summer
GRSM (Aug), f (T, RH, H+, Soil/sea salt)
New continuous measurement
applications
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Modify approach to permit gas + particle
measurement at 10-15 min time resolution
Measure ammonia emissions from dairies
–
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Make system mobile to permit upwind + downwind
measurements
Examine impacts of emitted ammonia on airborne
particle concentrations
Project runs: Fall 2005 – Summer 2008
Conceptual picture
+hv, VOC
NOx
HNO3 + NH3  NH4NO3(p)
Measurement approach
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Collect
particles in
liquid stream
Inject stream
into ion
chromatograph
for chemical
analysis
Switch
between
“gas+particle”
and “particle
only” sampling
Field deployment
November, 2005
Modified Particle-Into-Liquid Sampler
11/21/2005 12:00
11/21/2005 6:00
11/21/2005 0:00
11/20/2005 18:00
1.5
11/20/2005 12:00
11/20/2005 6:00
11/20/2005 0:00
11/19/2005 18:00
11/19/2005 12:00
11/19/2005 6:00
11/19/2005 0:00
11/18/2005 18:00
11/18/2005 12:00
11/18/2005 6:00
11/18/2005 0:00
11/17/2005 18:00
11/17/2005 12:00
µg/m3
Initial Observations - Sulfate
2.0
Total = particle + SO2
Particle sulfate
1.0
0.5
0.0
11/21/2005 12:00
11/21/2005 6:00
11/21/2005 0:00
11/20/2005 18:00
11/20/2005 12:00
7.5
7.0
6.5
6.0
5.5
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
11/20/2005 6:00
11/20/2005 0:00
11/19/2005 18:00
11/19/2005 12:00
11/19/2005 6:00
11/19/2005 0:00
11/18/2005 18:00
11/18/2005 12:00
11/18/2005 6:00
11/18/2005 0:00
11/17/2005 18:00
11/17/2005 12:00
µg/m3
Initial Observations - Nitrate
Total = particle + HNO3
Particle nitrate
11/21/2005 12:00
11/21/2005 6:00
11/21/2005 0:00
80
11/20/2005 18:00
90
11/20/2005 12:00
11/20/2005 6:00
11/20/2005 0:00
11/19/2005 18:00
11/19/2005 12:00
11/19/2005 6:00
11/19/2005 0:00
11/18/2005 18:00
11/18/2005 12:00
11/18/2005 6:00
11/18/2005 0:00
11/17/2005 18:00
11/17/2005 12:00
µg/m3
Initial Observations – Ammonia
100
Total = particle +NH3
Particle ammonium
70
60
50
40
30
20
10
0
Initial Conclusions
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Particle nitrate and sulfate
agree well with filter
measurements
Lots of ammonia
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–
–
–
>> particle ammonium
Denuders to remove
NH3(g) last only ~4-5
hours
Lose NH3(g) in instrument
Change sampler design
to better capture NH3(g)
2
P-NO3
P-SO4=
T-NO3
T-SO4=
1:1
1.5
URG (ug/m3)

1
0.5
0
0
0.5
1
PILS (ug/m 3)
1.5
2
Summary and future work
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Nitrate and sulfate important components of airborne particles
NH3(g) availability affects particle formation
–
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New approach to semi-continuous particle + gas measurements can help
resolve
–
–
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Emissions
Changes in particle amount and composition due to emissions
Modifications are needed to measurement approach to
–
–
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BUT, not all particle nitrate is NH4NO3
Improve NH3(g) collection efficiency (steam sampler)
Enhance capacity of denuder for NH3(g) removal in particle only measurement
Modified instruments will be redeployed
–
Look at particle and gas concentrations
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–
At high time resolution
Over longer periods than feasible for manual filter-pack sampling
Evaluate how emissions vary between source types on a dairy