Oxalic Acid, Oxalates, Malonic Acids & Malonates in Transboundary Biomass Burning Aerosols:
Measurements and Temporal Trends
Liming YANG and Liya E. YU Division of Environmental Science & Engineering
National University of Singapore
For
A&WMA International Specialty ConferenceLeapfrogging Opportunities for Air Quality Improvement
Xi’an, ShanxiChina
10-14 May, 2010
Oxalic Acid & Malonic AcidWhat has been reported in literature?
• 1980s – present: > 160 studies
• Locations:
Asia, Africa & America; Urban, suburban, and remote
& marine atmospheres
• Primary emissions
• Secondary organic aerosols
C2 DCA
C3 DCA
Oxalic Acid & Malonic AcidWhat has been reported in literature?
• > 125 studies: Most abundant DCAs
• Some studies: < detection limit
Oxalic acid in PM at the same location during winter,
• < detection limit
• most abundant DCA
• < detection limit
Solvent extraction → silylation → GC-MS analysis
• most abundant DCA
Water extraction → butylation → GC-MS analysis
Oxalic Acid & Malonic Acid
PM (Filter) samples
Water extraction
Additional sample preparatione.g., concentration, derivatization…
Instrumental analyses e.g., GC-MS, IC, …
Organic solvent extraction
What has been reported in literature?
Measurement ApproachesWhat have we learnt from reported studies?
Extraction approach
Derivatization(Analysis)
DetectionNo. of
studiesOxalic acid
Malonic acid
1. Water -- (IC) √√√√ √√√√ 67
2. Water -- (CE) √√√√ √√√√ 13
3. Organic solvents Methylation (GC/GC-MS)
ND ND 35
4. Organic solvents→ water
Propylation(GC/GC-MS)
√√√√ √√√√ 4
5. Water Butylation (GC/GC-MS)
√√√√ √√√√ 38
6. Organic solvents Silylation (GC/GC-MS)
ND √√√√ 16
Streamlined Approaches
Water Extraction
Approach (a)
IC
Aerosol Samples
Approach (a) – Approach (b) = DCA salts
⇒⇒⇒⇒ Total oxalates (oxalic acid + oxalate salts)
Approach (b)
Solvent Extraction
ICSolvent
Replacement (Solvents → water)
⇒⇒⇒⇒ Oxalic acid
Atmospheric DicarboxylatesImportance of atmospheric dicarboxylates
Hygroscopicity:
Sodium succinate (C4 dicarboxylate) > succinic acid
(Peng and Chan, Atmos. Environ., 2001)
Photooxidation rate:
Oxalates >> oxalic acid
(Yang et al., Atmos. Environ., 2008)
Transboundary Smoke of Biomass BurningBiomass Burning in Southeast Asia, 2008
Transboundary Smoke of Biomass BurningField Campaign, Singapore, 2008
• Duration: 16 September–5 October (JDs 260-279), 2008
• PM2.5 samples: 24-hour daily samples
• Analyses: Gravimetric measurements & organic speciation
Julian Day
260 265 270 275
PM
Co
ncen
trati
on
(µµ µµ
g m
-3)
0
10
20
30
40
50
PM10
PM2.5
Transboundary Smoke of Biomass BurningTemporal Trend in PM2.5 & PM10
During the smoke episode,
• PM10: 35.6–46.4 µg/m3; Average: 41.6 µg/m3, ~41% higher than the non-smoke episode period
• PM2.5: 13.9–24.0 µg/m3; Average: 19.2 µg/m3 , ~46% higher than the non-smoke episode period
Temporal Trend in Oxalic Acid and Oxalates
Julian Day
260 265 270 275
Oxala
tes (
ng
m-3
)
0
100
200
300
400
500
Oxali
c A
cid
(n
g m
-3)
0
20
40
60
80
100
120
Transboundary Smoke of Biomass Burning
During the smoke episode,
• Total oxalates (oxalic acid & oxalate salts): 186.7–423.7 ng/m3;
Average: 341.5 ng/m3, ~2.6 times of non-smoke episode period
• Oxalates: 169.9–398.0 ng/m3; Average: 312.2 ng/m3
• Oxalic acid: 16.8–51.9 ng/m3; Average: 29.3 ng/m3
Temporal Trend in Malonic Acid and Malonates
Julian Day
260 265 270 275
Malo
nate
s a
nd
Malo
nic
Acid
(n
g m
-3)
0
20
40
60
Malonicacid
Malonates
Transboundary Smoke of Biomass Burning
During the smoke episode,
• Total malonates (malonic acid & malonate salts): 58.7–80.9 ng/m3;
Average: 71.7 ng/m3, ~67% higher than non-smoke-episode period
• Malonates: 26.6–65.0 ng/m3; Average: 51.0 ng/m3
• Malonic acid: 12.1–39.8 ng/m3; Average: 20.6 ng/m3
Conclusions
During the smoke-episode period,
• PM10: 35.6–46.4 µg/m3, ~1.4 times of PM10 during non-smoke episode
• PM2.5: 13.9–24.0 ng/m3, ~1.5 times of PM2.5 during non-smoke episode
• [Oxalates + oxalic acid]: 186.7–423.7 ng/m3 , ~2.6 times of that during non-smoke-episode period
• [Malonates + malonic acid]: 58.7–80.9 ng/m3 ~1.7 times of that during non-smoke-episode period
Field Observations in 2008
Thank You !
Q&A
