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Chemistry of NO x and SOA: VOC Oxidation by Nitrate Radicals. Andrew Rollins Cohen research group, department of chemistry University of California, Berkeley, USA. NO x = NO + NO 2. O 2. O 3. h ν. Τ s.s. ~ minutes. NO. NO 2. O 2. O 3. OH, O 3. Aerosol Surface Area. SOA.

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chemistry of no x and soa voc oxidation by nitrate radicals

Chemistry of NOx and SOA:VOC Oxidation by Nitrate Radicals

Andrew Rollins

Cohen research group, department of chemistry

University of California, Berkeley, USA

no x no no 2
NOx = NO + NO2



Τs.s. ~ minutes






OH, O3






regional no x emission trends
Regional NOx Emission trends

Measured Göteborg


Estimates for total

Asian emissions

van Aardenne et al., Atmospheric Environment 33 (1999) 633Ð646

  • Motivations
    • Global/Regional changes in NOx:VOC 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
soa no x dependence effects on peroxy radical chemistry
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

nitrate radical no 32
Nitrate Radical (NO3)


[NO3]≈10’s ppt

Brown et al 2004

no 3 vs oh and o 3 as voc sinks
NO3 vs OH and O3 as VOC sinks

0.5 x 107 cm-3 = 0.2 ppt OH

20 ppt NO3

Brown et al 2004


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.
alkene oxidation by nitrate radicals
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.

J.H. Kroll, J.H. Seinfeld / Atmospheric Environment 42 (2008) 3593–3624

j lich chamber experiments
Jϋlich chamber experiments
  • SAPHIR chamber ~ 260 m3.
  • Near Ambient NOx & VOC
  • Long chamber runs (> 12 hours)
  • NO3 SOA experiments:
    • Linomene
    • Β-Pinene (high and low RH)
    • Isoprene (seeded)
isoprene no 3
Isoprene + NO3
  • 15 hour run
  • Max 10 ppb isoprene, 30 ppb NO2, 60 ppb O3
  • NH3(SO4)2 seed
  • Many NO3 / N2O5 measurements
isoprene c 5 h 8
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 47%5 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

chamber experiment additions
Chamber Experiment Additions

< 10% of isoprene consumed by O3


SOA from:

    • NO3 + initial oxidation products?
    • RO2 + RO2 vs RO2 + NO3?
chamber ro 2 fate
Chamber RO2 fate

RO2 + NO3 not expected to produce

Less volatile products than RO2 + RO2

modeling chemistry
Modeling Chemistry



Second generation

oxidation produts

role of secondary chemistry
Role of secondary chemistry



Isoprene → X → Y

2% Yield

Secondary oxidation products

Initial oxidation products

role of secondary chemistry1
Role of secondary chemistry



Isoprene → X → Y

2 0% Yield

10% Yield

Secondary oxidation products

Initial oxidation products

importance of no 3 nighttime oxidation
Importance of NO3 / nighttime oxidation



Apel et al 2002, JGR VOL. 107, NO. D3, 10.1029/2000JD000225

aerosol composition




Aerosol Composition











aerosol composition1
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.

Aerosol Composition
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

thermal dissociation laser induced fluorescence of aerosol nitrates
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
td lif aerosol organic nitrate
TD-LIF Aerosol Organic Nitrate

Remove gas phase NOy, pass aerosol

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





NOy Bubbler

Diffusion Dryer

Entrained Aerosol Flow Tube

hno 3 on nh 3 so 4 2 particles
HNO3 on NH3(SO4)2 particles

ω = 34100 cm/s

A = 5 x 10-3 cm2/cm3

γ = 0.006

no x aerosol research questions
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 BVOC’s.
    • Flow tube uptake measurements of organic nitrates / nitric acid on aerosol surfaces.
take home points
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 VOC’s are lower compared to oxidation products providing an increased opportunity for multiple oxidation steps, temperatures are lower.
  • Yields for SOA produced from VOC’s requiring multiple oxidations to achieve low enough vapor pressure for condensation may be underestimated.
thanks to
Cohen Group

Juliane Fry (Reed College, Oregon)

Ronald Cohen

Paul Wooldridge

F.Z. Jϋlich scientists

Astrid Kiendler-Scharr

Steve Brown, Hendrik Fuchs, Bill Dubé (NOAA)

Sarpong Group (UCB)

Walter Singaram

Massoud Motamed

Thanks to…