Chemistry of NOx and SOA: VOC Oxidation by Nitrate Radicals

1
Chemistry of NOx and SOA VOC Oxidation by
Nitrate Radicals

• Andrew Rollins
• Cohen research group, department of chemistry
• University of California, Berkeley, USA

2
NOx NO NO2
O2
O3
h?
?s.s. minutes
NO
NO2
O3
O2
3
OH, O3
Aerosol Surface Area
SOA
IPCC AR4
4
Regional NOx Emission trends
Measured Göteborg NO2
Estimates for total Asian emissions
van Aardenne et al., Atmospheric Environment 33
(1999) 633Ð646
5
outline

• Motivations
• Global/Regional changes in NOxVOC emissions
• NOx emissions as control strategy
• 2 classes of NOx effects on SOA production
• Product distributions / RO2 chemistry
• NO3 VOC ? SOA
• Nitrate Radical (NO3)
• Isoprene NO3 SAPHIR experiment
• Alkyl Nitrate kinetic uptake experiments

6
SOA NOx Dependence effects on peroxy radical
chemistry
RO2 HO2 vs RO2 NO
High NOx and VOC
High NOx and VOC
Unexplained / not always observed
Kroll et al. Environ. Sci. Technol. 2006, 40,
1869-1877 Presto et al. Environ. Sci. Technol.
2005, 39, 7046-7054
7
Nitrate Radical (NO3)
8
Nitrate Radical (NO3)
9
Nitrate Radical (NO3)
Sunset
NO310s ppt
Brown et al 2004
10
NO3 vs OH and O3 as VOC sinks
VOC kOH kO3 kNO3
Isoprene 102 1.28e-5 0.68
a-pinene 54 8.5e-5 6.2
Limonene 170 2.0e-4 12
Methacrolein 34 1.1e-6 4.4e-3
0.5 x 107 cm-3 0.2 ppt OH
20 ppt NO3
Brown et al 2004
11
Blodgett Forest Research Station (Sierra Nevada
Mountains, California) Summer 2007 average

• Decreased but significant BVOC remain at night.
• Isoprene emissions increase with temperature and
  light 10 isoprene processed by NO3.
• Products of daytime oxidation persist with high
  concentrations throughout the night.

12
Alkene Oxidation by Nitrate Radicals

• Decrease in vapor pressure of parent molecule
  upon addition of nitrate group is comparable to
  products of reaction with OH.
• NO3 reactions dominate at night lower
  temperatures, decreased boundary layer /
  increased concentrations.

group Pvap factor
ONO2 6.8 x 10-3
OH 5.7 x 10-3
OOH 2.5 x 10-3
J.H. Kroll, J.H. Seinfeld / Atmospheric
Environment 42 (2008) 35933624
13
J?lich chamber experiments

• SAPHIR chamber 260 m3.
• Near Ambient NOx VOC
• Long chamber runs (gt 12 hours)
• NO3 SOA experiments
• Linomene
• ?-Pinene (high and low RH)
• Isoprene (seeded)

14
Isoprene NO3

• 15 hour run
• Max 10 ppb isoprene, 30 ppb NO2, 60 ppb O3
• NH3(SO4)2 seed
• AMS, SMPS, PTRMS, GC, TDLIF
• Many NO3 / N2O5 measurements

15
Isoprene C5H8

• 440-6601 TgC / 13002 TgC total non-methane VOC
  (biogenic anthropogenic) 34 50 total
  carbon.
• Two double bonds/ multiple oxidation steps / high
  reactivity to OH, O3, NO3.
• Isoprene SOA potential is poorly understood,
  small yields of SOA (5 by NO3) could be large
  Fractions of total global SOA annual production
  (2-3 TgC / 12-70TgC)4
• Early OH and O3 experiments (100s of ppbs
  isoprene and NOx) concluded Isoprene not an SOA
  precursor, because 1st generation oxidation
  products of isoprene are too volatile. More
  recently photochemical experiments demonstrate
  that Isoprene possibly contributes up to 475 of
  global SOA, by polymerization and heterogeneous
  chemistry of initial oxidation products
• Alkyl Nitrate formation by addition of NO3
  observed with high (80) yields, increase MW and
  adding functionality. SOA yields reported at 4.3
  - 23.8 (increasing with existing OM).6

4Kanakidou et al. 2005 5Zhang et al. 2007 6Ng et
al. 2008
1Guenther et al. 2006 2Goldstein and Galbally
2007 3Calvert et al. 2000
16
Isoprene NO3 Products
17
Chamber Experiment Additions
lt 10 of isoprene consumed by O3
18
(No Transcript)
19

• SOA from
• NO3 initial oxidation products?
• RO2 RO2 vs RO2 NO3?

20
Chamber RO2 fate
RO2 NO3 not expected to produce Less volatile
products than RO2 RO2
21
Modeling Chemistry
NO3
kfit
Second generation oxidation produts
22
Role of secondary chemistry
NO3
NO3
Isoprene ? X ? Y
2 Yield
Secondary oxidation products
Initial oxidation products
23
Role of secondary chemistry
NO3
NO3
Isoprene ? X ? Y
2 0 Yield 10 Yield
Secondary oxidation products
Initial oxidation products
24
Importance of NO3 / nighttime oxidation
SAPHIR
Ambient
Apel et al 2002, JGR VOL. 107, NO. D3,
10.1029/2000JD000225
25
Aerosol Composition
NO3
NO3
NO3
RO2
NO3
Observed SOA Composition
polymerization, decomposition
26
Aerosol Composition

• High correlation between AMS nitrate, AMS organic
  and total alkyl nitrates signals indicates
  condensation of organic nitrate is responsible
  for majority of SOA
• High initial yield of nitrate formation from
  initial reaction
• Total mass observed requires SOA by oxidation of
  one of the organic nitrate products of isoprene
  NO3, not just MVK and MACR.

27

• AMS indicates 15 mass is nitrate mass
• High yield of nitrates from initial rxn and
  correlation of nitrate formation with SOA suggest
  multiple NO3 additions lead to aerosol.
• 2 observations indicate underestimation of
  aerosol nitrate, or NOx release upon SOA
  condensation

28
Thermal Dissociation Laser Induced Fluorescence
of Aerosol Nitrates

• Thermal desorption of semivolatiles
• Thermal dissociation of nitrates
• LIF detection of NO2
• Measurements of total aerosol bound nitrate mass
  in
• HNO3
• Organic Nitrates

29
TD-LIF Aerosol Organic Nitrate
Remove gas phase NOy, pass aerosol

• Coupled to entrained aerosol flow tube for
  measurement of uptake coefficients

30
Pneumatic Nebulizer, (NH4)2SO4 droplets
NOy Bubbler
Diffusion Dryer
Entrained Aerosol Flow Tube
31
HNO3 on NH3(SO4)2 particles
? 34100 cm/s A 5 x 10-3 cm2/cm3 ? 0.006
32
Uptake of synthesized organic nitrates

• Salts
• Organic particles

33
NOx / Aerosol Research Questions

• Effects of changing NOx / VOC emissions on the
  total SOA production, and speciation.
• Total yield changes?
• Aerosol composition? If composition, is CCN
  affected?
• Current research
• Chamber SOA and organic nitrate aerosol yields /
  mechanisms from NO3 oxidation of BVOCs.
• Flow tube uptake measurements of organic nitrates
  / nitric acid on aerosol surfaces.

34
Take Home Points

• Regulation of NOx emissions is a primary control
  strategy and we should expect NOx / VOC ratios
  will change with significant regional
  differences.
• NO3 chemistry important for producing higher MW
  organics, is active at night when concentrations
  of primary VOCs are lower compared to oxidation
  products providing an increased opportunity for
  multiple oxidation steps, temperatures are lower.
• Yields for SOA produced from VOCs requiring
  multiple oxidations to achieve low enough vapor
  pressure for condensation may be underestimated.

35
Thanks to

• Cohen Group
• Juliane Fry (Reed College, Oregon)
• Ronald Cohen
• Paul Wooldridge
• F.Z. J?lich scientists
• Astrid Kiendler-Scharr
• Steve Brown, Hendrik Fuchs, Bill Dubé (NOAA)

• Sarpong Group (UCB)
• Walter Singaram
• Massoud Motamed