Transcript Document 7145702

Characterization of Aerosol Nitrate and
its Measurement at IMPROVE sites
Jeffrey L. Collett, Jr.
Colorado State University
Acknowledgments

Funding
–
–

Co-PI
–

Sonia Kreidenweis
Field and lab work
–
–

NPS/IMPROVE
LAWFR
Taehyoung Lee
Xiao-Ying Yu
Project support
–
–
UC Davis
Air Resource Specialists
Motivation




Nitrate is an important
contributor to PM at many
locations, especially in
Midwestern and Western
U.S.
Nitrate may become more
important if sulfate
concentrations decrease
Sampling methodology
developed with focus on
sulfate
Nitrate may be present in
fine or coarse modes and
in different chemical forms
Nitrate characteristics


Chemical form of nitrate
HNO3(g) + NH3(g) NH4NO3(p)
f(T, RH)
HNO3(g) + NaCl(p)  NaNO3(p) + HCl(g)
sea salt
2 HNO3(g) + CaCO3(p)  Ca(NO3)2(p) + CO2 + H2O
soil
Nitrate particle size
–
–
Fine mode, submicron [NH4NO3]
Coarse mode, supermicron [NaNO3, Ca(NO3)2]
Nitrate in Big Bend N.P. (BRAVO)

The sea salt link
–
–
High
particulate
nitrate
associated
with flow from
Gulf
Not
necessarily
high when
total nitrate
(including
HNO3(g)) was
high
Nitrate in Big Bend N.P. (BRAVO)
The sea salt
link
–
–
Sea salt
aerosol
deficient in
ClNO3correlated
with Na+
Typical sea salt ratio line
Slope = 1.798
0.2
0.15
0.1
R2 = 0.69
0.05
0
0
0.05
0.1
0.15
Na+(µg/m3)
0.2
0.25
0.6
0.5
[NO3-] (µg/m3)

[Cl-] (µg/m3)
0.25
R2 = 0.64
0.4
0.3
0.2
0.1
0
0
0.1
0.2
[Na+] (µg/m3)
0.3
Nitrate in Big Bend N.P. (BRAVO)
–
–

Mode size
~4-5 µm
Size
distribution
similar to Na+
PM2.5 size cut
does not
separate fine
and coarse
modes well
25
350
dC/dlog(Dp) (neq/m3)
Found in
coarse
mode
particles
300
nitrate
sulfate
20
250
15
200
150
10
100
5
50
0
0
0.1
dC/dlog(Dp) (neq/m3)

1
10
100
0.1
1
10
100
10
100
30
250
ammonium
200
sodium
25
20
150
15
100
10
50
5
0
0
0.1
1
10
Aerodynam ic Diam eter (µm )
100
0.1
1
Aerodynam ic Diam eter (µm )
Nitrate replacement

NH4NO3 formation not favored
thermodynamically in acidic
aerosol
–
NH3(g) will first neutralize sulfate


H2SO4 NH4HSO4 (NH4)2SO4
Once aerosol is neutralized,
NH4NO3 formation may occur
–

SO4298 g/mole
f(T,RH)
If SO42- is decreased, NO3- may
replace it
–
–
Two NO3- replace each SO42Sulfate reduction could produce
PM mass increase
NO3NO362 g/mole 62 g/mole
Potential for NH4NO3 formation in
BBNP
NH4NO3 could form
–


12
Considerable “excess” sulfate
means large decrease in sulfate
often required before aerosol
neutralized
NH4NO3 formation also not favored
by high T and low RH
)
SO4=
3

BBNP aerosol acidic
If SO42- decreases aerosol
could become neutralized
Concentration (µg/m

10
8
Excess SO4=
Total nitrate(HNO3 + NO3-)
6
4
2
0
8
/2
10
1
/2
10
4
/1
10
/7
10
30
9/
23
9/
16
9/
9
9/
2
9/
26
8/
19
8/
12
8/
5
8/
29
7/
22
7/
15
7/
8
7/
1
7/
What is nitrate situation elsewhere?

Eastern U.S.
–
Model studies show
potential for aerosol
mass increase as
nitrate replaces
sulfate in response to
declining sulfate
concentrations

Western U.S.
–
–
Little known about
potential for nitrate
replacement of sulfate
Large uncertainties in
current aerosol
composition



Acidity?
Ammonia/ammonium?
Is existing nitrate
NH4NO3?
Summer 2002 Yosemite NP study
 24 hr URG PM2.5 cyclone/annular denuder/
filter pack sampler
 24 hr MOUDI impactor
 15 min PM2.5 PILS/IC system
Particle into Liquid Sampler
Ion Chromatograph
Yosemite
results
POM
Black C
2%
Oxalate
1% Na+
Soil
6%
1%


Carbon-dominated
aerosol
(NH4)2SO4 dominant
salt
Soil
Cl-
NH4+
4%
Ions
19%
POM
73%
Black C
NO2NO3-
K+
0%
SO42Oxalate
Mg2+
0%
SO4210%
Na+
NH4+
Ca2+
0%
NO33% NO20%
K+
Mg2+
Cl0%
Ca2+
URG sampler
45
40
NO3-
SO4=
NH4+
35
neq/m3
30
25
20
15
10
5
0
7/14
7/17
7/20
7/23
7/26
7/29
8/1
8/4
8/7
8/10
8/13
8/16
8/19
8/22
8/25
8/28
8/31
9/3
20
Cl- or ((NO3-)+(Cl-))
(neq/m3)
NH4NO3
Yosemite
results - II
15
10
Na+ vs. ClNa+ vs.((NO3-)+(Cl-))
Slope for sea water (1.164)
5
What about nitrate?
–
–
0
0
NaNO3 present at most times

5
10
15
20
Na+ (neq/m3)
Note Cl- present when Na+ > NO3-
NH4NO3 dominant a few times (not shown)
30
2-week excerpt, PILS 15-min data
25
Cl-
NO3-
Na+
20
neq/m3

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
Yosemite results - III

Ion size distributions again show predominance of coarse
mode nitrate
MOUDI trace ion average distributions (August)
3
NH4+
SO4=
Na+
NO3Cl-
12
8
2
2
6
1
4
aerodynamic diameter
>18.0
10.0 - 18.0
5.6 - 10.0
3.2 - 5.6
1.8 - 3.2
1.0 - 1.8
0
0.56 - 1.0
0
0.32 - 0.56
1
0.18 - 0.32
2
< 0.18
NH4+ and SO4=
(neq/m3)
10
3
Na+, NO3-, and Cl(neq/m3)
14
IMPROVE ion special study goals

Determine characteristics of ionic aerosol present at
selected IMPROVE sites
–
–
–

Evaluate IMPROVE ion sampling and analysis
approach
–
–

Ionic composition
Ion size distributions
Gas-particle distribution of NH3(g)/NH4+(p) and HNO3(g)/NO3-(p)
Utilize field and lab studies
Filter choice, Filter extraction method, and denuder protocol
How might fine particle nitrate change in response to
sulfate concentration decreases or other changes?
IMPROVE ion study field
campaigns

6 one-month campaigns



–
–

Bondville (midwest) - February
2003
San Gorgonio (southern CA) –
April and July 2003
Grand Canyon – May 2003 (cosponsored by LAWFR)
Brigantine (NE coastal) –
November 2003
Sequoia (Sierra Nevada) –
February 2004
Measurements
–
–
–
MOUDI sampler – ion size
distributions
3 Parallel URG denuder/filterpack samplers running different
protocols
PILS sampler – 15 minute PM2.5
anions and cations
•Modules 1 and 2
PM2.5
HNO3 denuder
NH3 denuder
N filter (IC)
HNO3 denuder
NH3 denuder
•Undenuded sampling on
Teflon filter
NH3 denuder
•Aerosol acidity/NH4NO3
volatilization
NH3 denuder
•Replicates for precision
HNO3 denuder
•Day/night sampling
Filter A
N filter (H2O)
HNO3 denuder
•Module 3
PM2.5
•Provide gas-particle phase
distribution for N(-III) and
N(V)
NH3 denuder
•Examine loss of HNO3 and
NH3 from nylon filter
HNO3 denuder
•Compare nylon filter
extraction (H2O vs.
carbonate/bicarbonate)
PM2.5
•Daily, 24 hr samples
Bondville
highlights
February 2003
Variable composition

NO3- and SO42- both
important
NO3-
12
SO4=
10
8
6
4
2
NH4NO3 observed in
submicron mode
2/26
2/24
2/22
2/20
2/18
2/16
2/14
2/12
2/10
2/8
2/6
0
2/4
–
14
2/2

16
SO4= and NO3-µg/m3

Bondville Anions
Bondvile PM2.5 - 2/03
400
2/3/03
600
Conc. (µN)
500
NO3-
SO4=
NH4+
400
300
200
100
0
Concentration (neq/m3)
350
NO3- + SO42NH4+
300
250
200
150
100
50
< 0.18 0.18 - 0.32 - 0.56 0.32 0.56
1.0
1.0 1.8
1.8 3.2
Stages
3.2 5.6
5.6 10.0
10.0 - >18.0
18.0
0
2/1
2/3
2/5
2/7
2/9 2/11 2/13 2/15 2/17 2/19 2/21 2/23 2/25 2/27
Sampling and extraction issues

Does water efficiently extract
nitrate from nylon filters?
–

Nitric acid collected on nylon
filters not efficiently recovered
with water extraction
What happens to NH4NO3
volatilized from nylon filters?
–
–
NH3(g) + HNO3 (g)  NH4NO3(p)
HNO3 trapped? Decrease in
water extraction efficiency?
NH3 lost? Bias in measured
PM2.5 ammonium?
NH4NO3
NH3(g)
Nylon filter (DI water extract) µg/m3
NO3- comparison
Bondville
test results

Nylon filter
extraction by
water looks
good
20
15
10
5
0
0
5
10
15
20
Nylon filter (IC eluent extract)
µg/m3
Nylon filter losses - Bondville
0.3

Up to 18% of
NH4+ lost from
nylon filter
Fraction lost
NH4+
NO3-
0.2
0.1
0
1/29
2/3
2/8
2/13
2/18
2/23
2/28
3/5
San Gorgonio highlights


April 2003
Sample analysis results still
being processed


PILS shows lots of NH4NO3
Peak NH4NO3 ~ 45 µg/m3 at
17:00 on April 9th
San Gorgonio (4/4/03 - 4/26/03)
700
600
neq/m3
500
NH4+ neq/m3
NO3- neq/m3
SO42- neq/m3
400
300
200
100
0
4/4 4/5 4/6 4/7 4/8 4/9 4/10 4/11 4/12 4/13 4/14 4/15 4/16 4/17 4/18 4/19 4/20 4/21 4/22 4/23 4/24 4/25 4/26
Grand Canyon
highlights
Grand Canyon timelines of Anions
2
ClNO3-
0.5
Concentrations
similar to
IMPROVE
historic data
5/23
5/24
5/25
5/26
5/27
5/28
5/29
5/30
Grand Canyon timelines of cations
1
Na+
NH4+
Ca2+
0.75
0.5
0.25
5/30
5/28
5/29
5/26
5/27
5/24
5/25
5/22
5/23
5/20
5/21
5/18
5/19
5/16
5/17
5/14
5/15
5/12
5/13
5/10
5/11
5/8
5/9
0
5/6
5/7
NH4+, Na+, and
Ca2+ all important
cations
5/8
5/9
5/10
5/11
5/12
5/13
5/14
5/15
5/16
5/17
5/18
5/19
5/20
5/21
5/22
5/1
5/2
5/3
5/4
5/5
5/6
5/7
0
5/4
5/5

1
5/2
5/3
–
SO4=
5/1

May 2003
Variable
composition with
sulfate dominating
by mass
µg/m3

µg/m3
1.5
Grand Canyon

Enough
NH4+ to
neutralize
sulfate
Grand Canyon
45
40

Is NO3paired with
Na+ and/or
Ca2+ ?
Conc. (neq/m3)
35
30
25
SO42Na+
Ca2+
NO3NH4+
20
15
10
5
0
4/29
5/4
5/9
5/14
5/19
5/24
5/29
6/3
Grand Canyon
12
10

Concentration (neq/m3)
Grand Canyon
Sea salt deficient in Cl-
8
Cl6
NO3- + Clsea salt
4
2
NO3- shows some
“tracking” with Na+ and
Ca2+
20
Concentration (neq/m3)

0
0
2
4
6
8
10
Na+ (neq/m3)
NO3Na+
15
Ca2+
10
5
0
5/7
5/8
5/9
5/10
5/11
5/12
5/13
5/14
5/15
5/16
5/17
5/18
5/19
Grand Canyon
Fine mode is (NH4)2SO4
Coarse mode is complex mix of
Na+, Ca2+, NO3-, and SO42Fine and coarse modes again
separated at ~ 1 µm





NO3- and Na+ have similar size
distributions but NO3- > Na+
HNO3 rxns. with sea salt and soil
dust both important
Grand Canyon MOUDI average
12
SO4=
10
NH4+
neq/m3
8
NO36
Na+
4
Ca2+
2
0
< 0.18
0.18 - 0.32
0.32 - 0.56
0.56 - 1.0
1.0 - 1.8
1.8 - 3.2
aerodynamic diameter (µm)
3.2 - 5.6
5.6 - 10.0
10.0 - 18.0
>18.0
Grand Canyon test results
Water again efficient for NO3extraction from nylon filter

–
NO3- comparison
not yet corrected for denuder
efficiency
1
Nylon filter losses - Grand Canyon
0.8
0.7
0.6
0.4
0.2
0
0
0.2
0.4
0.6
0.8
Nylon filter (IC eluent extract)
µg/m3
1
Fraction lost from nylon filter
Nylon filter DI water extract (µg/m3)
NH4+ loss from nylon filter again
evident
0.6
NH4+
0.5
NO3-
0.4
0.3
0.2
0.1
0
5/1
5/2
5/3
5/4
5/5
5/6
5/7
5/8
5/9
5/10
5/11
5/12
5/13
5/14
5/15
5/16
5/17
5/18
5/19
5/20
5/21
5/22
5/23
5/24
5/25
5/26
5/27
5/28
5/29
5/30

Grand Canyon gas concentration
1
Grand Canyon
gas phase
HNO3(g)
SO2(g)
0.8
µg/m3
NH3(g)
0.6
0.4
0.2

5/30
5/28
5/29
5/25
5/26
5/27
5/23
5/24
5/21
5/22
5/18
5/19
5/20
5/16
5/17
5/14
5/15
5/11
5/12
5/13
5/9
5/10
5/7
5/8
5/4
5/5
5/6
5/2
5/3
5/1
0
1
HNO3/N(V)
SO2/(SO2+SO4=)
0.8
NH3/N(-III)
0.6
0.4
0.2
0
5/1
5/2
5/3
5/4
5/5
5/6
5/7
5/8
5/9
5/10
5/11
5/12
5/13
5/14
5/15
5/16
5/17
5/18
5/19
5/20
5/21
5/22
5/23
5/24
5/25
5/26
5/27
5/28
5/29
5/30

Gaseous HNO3, NH3
and SO2 give potential
for additional PM2.5
formation
HNO3 is highest,
indicating potential for
additional particle
nitrate formation
Most nitrate is
currently in the gas
phase
Ratio


Grand Canyon
nitrate formation

–
–
–
–


PM2.5 assumed internally mixed
no Ca2+ in model
Measured T
Varied RH (20 and 50%)
No NH4NO3 formation predicted
even at 50% RH
–
ISORROPIA aerosol
thermodynamic model used to
simulate aerosol composition
Important model limitations

Decrease sulfate and watch
what happens
Formation at night (low T, high
RH) ?
Mass increase on 5/2 and 5/5 for
25% SO42- comes from
replacement of Na2SO4 by
NaNO3
Grand Canyon ISORROPIA mass for 50% RH
3.0
2.5
µg/m3
2.0
1.5
1.0
0.5
0.0
4/30
5/2
5/4
5/6
5/8
5/10
5/12
100% SO4=
5/14
75% SO4=
5/16
5/18
50% SO4=
5/20
5/22
25% SO4=
5/24
5/26
5/28
5/30
Summary and PRELIMINARY
Conclusions

Nitrate may be present in
–
Submicron ammonium nitrate particles


–
Coarse mode sodium or calcium nitrate particles




Big Bend NP, TX
Grand Canyon NP, AZ
Yosemite NP, CA
PM1 size cut would better separate coarse and fine modes than
PM2.5
Use of a nylon filter with deionized water extraction
–
–

Bondville, IL
San Gorgonio, CA
No strong bias observed (yet) in nitrate recovery
May yield negatively biased NH4+ concentrations
Sulfate reductions at Big Bend and Grand Canyon appear unlikely
to produce increases in PM mass
Future Work


Continue analysis of data from San Gorgonio,
Bondville, and Grand Canyon
Complete 1-month campaigns in
–
–


Brigantine, NJ
Sequoia NP, CA
Mobile laboratory?
Recommend procedures for accurate measurement
of IMPROVE PM ion composition
Initial findings

Nylon filter extraction by water?
–
–

EPA study of fall filters collected at numerous STN
and IMPROVE sites gave average 90% extraction
efficiency
CSU Fort Collins samples (Spring 2002) yielded no
evidence of lower water extraction efficiency
Fate of volatilized NH4NO3?
–
EPA study indicated significant ammonia loss
IMPROVE sampling approach


4 modules
Module B for PM2.5 ions
–
–
Carbonate-coated denuder removes acidic gases
Nylon filter


Extracted with carbonate/bicarbonate solution (anion IC
eluent) for anion analysis
Extracted with water for anion + cation analysis
–

Sodium interference from IC eluent
Analyzed by IC