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

h ν

O 3 NO 2 NO

Τ

s.s.

~ minutes

O 2 O 3

Aerosol Surface Area

OH, O 3

SOA IPCC AR4

Regional NO x Emission trends Measured Göteborg NO 2 Estimates for total Asian emissions van Aardenne

et al., Atmospheric Environment

33 (1999) 633

Ð

646

outline  Motivations    Global/Regional changes in NO x :VOC emissions NO x emissions as control strategy  2 classes of NO x effects on SOA production  Product distributions / RO 2 chemistry NO 3 + VOC → SOA    Nitrate Radical (NO 3 ) Isoprene + NO 3 SAPHIR experiment Alkyl Nitrate kinetic uptake experiments

SOA NO x Dependence: effects on peroxy radical chemistry RO 2 + HO 2 vs RO 2 + NO Unexplained / not always observed High NO x Kroll

et al

. Environ. Sci. Technol.

2006

, 40, 1869-1877 Presto

et al

. Environ. Sci. Technol.

2005

, 39, 7046-7054

Nitrate Radical (NO 3 ) NO 3 NO 

h ν

 NO 3 

τ

     2NO 2 NO O 3 NO  2 NO  2 NO    NO 3 3   O   N 2 O 5 2 x

Nitrate Radical (NO 3 ) NO 3 NO 

h ν

 NO 3 

τ

     2NO 2 NO O 3 NO  2 NO  2 NO    NO 3 3   O   N 2 O 5 2 x

Nitrate Radical (NO 3 ) NO 3 NO 

h ν

 NO 3 

τ

     2NO 2 NO O 3 NO  2 NO  2 NO    NO 3 3   O   N 2 O 5 2 x Sunset [NO 3 ]≈10’s ppt Brown et al 2004

NO 3 vs OH and O 3 as VOC sinks VOC Isoprene α-pinene Limonene Methacrolein k OH 102 54 170 34 k O3 k NO3 1.28e-5 0.68

8.5e-5 2.0e-4 1.1e-6 6.2

12 4.4e-3 0.5 x 10 7 cm -3 = 0.2 ppt OH 20 ppt NO 3 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 NO 3 .

Products of daytime oxidation persist with high concentrations throughout the night.

Alkene Oxidation by Nitrate Radicals group ONO 2 OH OOH P vap factor 6.8 x 10 -3 5.7 x 10 -3 2.5 x 10 -3   Decrease in vapor pressure of parent molecule upon addition of nitrate group is comparable to products of reaction with OH.

NO 3 reactions dominate at night: lower temperatures, decreased boundary layer / increased concentrations.

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

J ϋlich chamber experiments     SAPHIR chamber ~ 260 m 3 . Near Ambient NO x VOC & Long chamber runs (> 12 hours) NO 3   SOA experiments: Linomene Β-Pinene (high and low RH)  Isoprene (seeded)

Isoprene + NO 3  15 hour run     Max 10 ppb isoprene, 30 ppb NO 2 , 60 ppb O 3 NH 3 (SO 4 ) 2 seed AMS, SMPS, PTRMS, GC, TDLIF Many NO 3 / N 2 O 5 measurements

Isoprene C 5 H 8      440-660 1 TgC / ~1300 2 TgC total non-methane VOC (biogenic + anthropogenic) ≈ 34 – 50% total carbon.

Two double bonds/ multiple oxidation steps / high reactivity to OH, O 3 , NO 3 .

Isoprene SOA potential is poorly understood, small yields of SOA (5% by NO 3 ) could be large Fractions of total global SOA annual production (2-3 TgC / 12-70TgC) 4 Early OH and O 3 experiments (100s of ppbs isoprene and NO x ) concluded Isoprene not an SOA precursor, because 1 st 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 NO 3 observed with high (80%) yields, increase MW and adding functionality. SOA yields reported at 4.3% - 23.8% (increasing with existing OM).

6 1 Guenther

et al

. 2006 2 Goldstein and Galbally 2007 3 Calvert et al. 2000 4 Kanakidou

et al.

2005 5 Zhang

et al.

6 Ng

et al.

2007 2008

Isoprene + NO 3 Products

3-4% 3-4% 70-80%

Chamber Experiment Additions < 10% of isoprene consumed by O 3

SOA from: •NO 3 + initial oxidation products?

•RO 2 + RO 2 vs RO 2 + NO 3 ?

Chamber RO 2 fate RO 2 + NO 3 not expected to produce Less volatile products than RO 2 + RO 2

Modeling Chemistry NO 3

k fit

Second generation oxidation produts

Role of secondary chemistry

Isoprene

→ X → Y

γ   SOA  Isoprene 2% Yield Initial oxidation products Secondary oxidation products

Role of secondary chemistry

Isoprene

→ X → Y

γ   SOA  Isoprene 2 0% Yield 10% Yield Initial oxidation products γ   SOA  1 st Gen.Prod

.

Secondary oxidation products

Importance of NO 3 / nighttime oxidation SAPHIR Ambient Apel et al 2002, JGR VOL. 107, NO. D3, 10.1029/2000JD000225

Aerosol Composition

3-4% 3-4% 70-80%

NO 3 NO 3 RO 2 Observed SOA Composition polymerization, decomposition NO 3 NO 3

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 + NO 3 , not just MVK and MACR.

  AMS indicates 15% mass is nitrate mass High yield of nitrates from initial rxn and correlation of nitrate formation with SOA suggest multiple NO lead to aerosol.

3 additions  2 observations indicate underestimation of aerosol nitrate, or NO x release upon SOA condensation

Thermal Dissociation Laser Induced Fluorescence of Aerosol Nitrates 1.

2.

3.

Thermal desorption of semivolatiles Thermal dissociation of nitrates: XNO 2   X  NO 2 LIF detection of NO 2    Measurements of total aerosol bound nitrate mass in: HNO 3 Organic Nitrates

TD-LIF Aerosol Organic Nitrate Remove gas phase NO y , pass aerosol  Coupled to entrained aerosol flow tube for measurement of uptake coefficients

Pneumatic Nebulizer, (NH 4 ) 2 SO 4 droplets Diffusion Dryer Entrained Aerosol Flow Tube NO y Bubbler

HNO 3 on NH 3 (SO 4 ) 2 particles

k

 

A

 4

ω =

34100 cm/s A = 5 x 10 -3 cm 2 /cm 3

γ

= 0.006

Uptake of synthesized organic nitrates •Salts •Organic particles

NO x / Aerosol Research Questions   Effects of changing NO x / 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 NO 3 oxidation of BVOC’s.

Flow tube uptake measurements of organic nitrates / nitric acid on aerosol surfaces.

Take Home Points    Regulation of NO x emissions is a primary control strategy and we should expect NO x / VOC ratios will change with significant regional differences.

NO 3 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)   Paul Wooldridge F.Z. J ϋlich scientists  Ronald Cohen Astrid Kiendler Scharr Steve Brown, Hendrik Fuchs, Bill Dubé (NOAA)  Sarpong Group (UCB)  Walter Singaram  Massoud Motamed