Uncertainties in the atmospheric oxidation of biogenic volatile organic compounds (BVOCs) : implications for air quality and climate Jingqiu Mao (Princeton/GFDL)

Uncertainties in the atmospheric oxidation of biogenic volatile organic compounds (BVOCs) :

implications for air quality and climate

Jingqiu Mao (Princeton/GFDL)

Yale University, 02/20/2014

Acknowledgement

Measurements: William Brune (Penn State), Xinrong Ren (NOAA/UMD)

Modeling: Fabien Paulot (Harvard), Daniel Jacob(Harvard), Ron Cohen (UC Berkeley), Paul Wennberg(Caltech), Larry Horowitz(GFDL)

BEARPEX science team (Biosphere Effects on Aerosols and Photochemistry Experiment)ICARTT science team (International Consortium on Atmospheric Transport and Transformation)SENEX science team (Southeast Nexus)

O3

O2

O3

OH HO2

hn, H2O

Deposition

NO

H2O2

CH4, CO, VOCs

NO2

STRATOSPHERE

TROPOSPHERE

8-18 km

Tropospheric radical chemistry

Air Quality

Climate

hn

hn

NOx = NO + NO2

HOx = OH + HO2

Global Emissions (Tg/yr)

0

200

400

600

Isoprene Methanol Other BiogVOCs

All AnthroVOCs

VOCs affect air quality and climate

Isoprene

Most important non-methane VOCGlobal emissions ~ methane(but > 104 times more reactive) ~ 6x anthropogenic VOC emissions

How we understand isoprene oxidation…ten years ago!

OH

Organic peroxy radicals

NOx

~10%

~90%

Alkyl nitrates

HCHO + MVK + MACR + other compounds

HO2

Organic peroxides

deposited Terminal sink for radicals

Terminal sink for radicals

IsopreneRO2

ROOH

RONO2

• OH is the main driver for isoprene oxidation!• OH concentration can be modulated by isoprene.

NO2

O3

NO

h

Part 1 : Uncertainties in OH concentrations

Model underestimates measured OH by a factor of 2-10 in forested regions.

(Lelieveld et al., Nature, 2008)

Pristine forests over South America

(Hofzumahaus, Science, 2009) (Ren et al., 2008, JGR)

Southern China (isoprene-rich)

Eastern US(isoprene-rich)

OH

Organic peroxy radicals

NOx

~10%

~90%

Alkyl nitrates

HCHO + MVK + MACR + other compounds

HO2

Organic peroxides

deposited Terminal sink for radicals

Terminal sink for radicals

IsopreneRO2

ROOH

RONO2

New understanding on the fate of organic peroxides

OH

O OH

+ OH

(Paulot et al., 2009, Science)

Epoxide

• Epoxide is an important precursor for secondary organic aerosols.

• Regeneration of OH from epoxide was not enough to close the gap.

OH

Organic peroxy radicals

NOx

~10%

~90%

Alkyl nitrates

HCHO + MVK + MACR + other compounds

HO2

Organic peroxides

Terminal sink for radicals

Isoprene

RO2

ROOH

RONO2

OH

O OH

+ OH

(Peeters et al., 2009, Phys. Chem. Chem. Phys.)

The third pathway proposed by Peeters et al. – unimolecular isomerization!

HOOO

isomerization

OHphotolysis

HPALDTo match observed OH, isomerization needs to be much faster than other channels!

Epoxide

This was a theoretical prediction!

If the isomerization is fast, the impact on global OH is huge!

(Taraborrelli et al., 2012, Nature Geoscience)

• this increases global OH by 14%, from 1.08 to 1.22 x 106 molecules cm-3.• methane lifetime is reduced from 8.0 to 7.2 years.

o Current observation-based estimate is 9.1 ± 0.9 years (Prather et al., 2012, GRL)

OH + isoprene → n OH

Laboratory measurements show much slower rate of isomerization…

Percentage of peroxy radicals going through isomerization

OH discrepancy still exists!

(Wolfe et al., 2012, PCCP)

(Crounse et al., 2011, PCCP)

laser

electronics

Vacuum pumps

optical fibers

OH cellHO2 cell

scaffolding tower

laboratory

inlet

(b)

A new study – BEARPEX 2007/2009

Located at the University of California Berkeley Blodgett Forest Research Station

Bitter Experimentalists Always Repairing Pieces of Equipment eXperiment

Biosphere Effects on Aerosols and Photochemistry Experiment

-40 -30 -20 -10 0 10 20 30 400

50

100

150

200

250

300

350

400

wavelength

OH

sig

na

l

OH difference by wavelength

off-line

on-line

off-line

off-line off-line

on-line

OH measured by the traditional Laser induced fluorescence (LIF) method …

Laser

Air

Vacuum Pump

OH cell308 nm

change wavelength between on-line (OH fluorescence) to off-line (background) every 20 sec (called OHwave).

and also by a second method …

• remove OH with an OH reactant (called chemical modulation or OHchem) every two minutes

Laser

Air

Vacuum Pump

OH cell308 nm

OH scrubber

(Mao et al., 2012, ACP)

The results were really shocking…!

• The high OH measured in forests are likely biased due to some instrumental interference.

• This interference is confirmed by other instruments.

Traditional measured OH

OH measured by the new method, “true” OH

(Mao et al., 2012, ACP)

The interference signal increases with temperature, pointing to the evidence of BVOCs!

Temperature (K)

OH does not deplete at high temperature (high BVOCs), suggesting some level of OH recycling in the atmosphere.

Traditional measured OH

OH measured by the new method, “true” OH

(Mauldin et al. Nature, 2013)

One possible candidate for causing this interference is Criegee Intermediate

Criegee Intermediate is found to be ubiquitous in forests.

Summary on OH uncertainties

• OH discrepancy between measurements and modeling may be largely due to the instrumental inferences, likely from oxidation products from BVOCs.

• OH recycling from isoprene oxidation does exist, but not as strong as theoretical study suggested.

Part 2: Uncertainties in ozone production

OH

Organic peroxy radicals

NOx

~10%

~90%

Alkyl nitrates

HCHO + MVK + MACR + other compounds

HO2

Organic peroxides

Terminal sink for radicals

Isoprene

RO2

ROOH

RONO2

OH

O OH

+ OH

HOOO

isomerization

OHphotolysis

HPALD

Epoxide

Uncertainties on ozone production

OH

NOx

~10%

~90%

Alkyl nitrates

HCHO + MVK + MACR + other compounds

Terminal sink for NOx and HOxIsoprene

RO2RONO2

NO2

O3

NO

hCompetition between ozone production and suppression

Major uncertainties lie in two aspects:

• How much RONO2 is produced, experimental results vary from 4% to 12%.

• What is fate of RONO2? Will they release NOx after degradation?

If these nitrates act as HNO3, they will be a sink for both NOx and HOx (0% recycling).

If they react with OH/O3 and release NOx, they will recycle NOx (100% recycling).

The conclusion can differ by more than 10 ppb depending on different assumptions on the recycling efficiency.

(Ito et al., 2009, JGR)

Response of summer surface ozone to an increase in BVOC emissions caused by a 5K temperature increase…

First generation of isoprene nitrates degraded to second generation nitrates!

OH

ONO2

ISOPN (1,4)

OH

ONO2

ISOPN (1,2)

OH

ONO2

ISOPN (4,3)

ONO2

OH

ISOPN (4,1)

O

OH

ONO2

methylvinylketone nitrate (MVKN)

O

ethanal nitrate(ETHLN)

O

propanone nitrate(PROPNN)

O

methacrolein nitrate(MACRN)

ONO2

OH

OH/O2

OH

ONO2

OH

OO

NO

OH

ONO2

OH

O

OH

ONO2

OH

OO

NO

OH

ONO2

OH

O

ONO2

OH

OH

OO

NO

ONO2

OH

OH

O

OH

ONO2

OH

OO

NO

OH

ONO2

OH

O

OH/O2OH/O2OH/O2

O2NO

O2NO

Second generation isoprene nitrates (C3-C4)

First generation isoprene nitrates (C5)

Laboratory measurements show that recycling efficiency is around 55%!

(Paulot et al., 2009, ACP)

The International Consortium on Atmospheric Transport and Transformation (ICARTT) aircraft study: July-August 2004

Extensive measurements on isoprene oxidation products, including total alkyl nitrates (∑ANs)

Chemical transport model (GEOS-Chem)

What is so unique for Eastern US?

(Millet et al., 2008, JGR)(Martin et al., 2008, AE)

Surface NOx is mainly produced from anthropogenic activities

HCHO is mainly produced from biogenic emissions (isoprene in particular)

Anthropogenic + Natural

A new isoprene chemistry for global models

(Mao et al., JGR, 2013)

ISOPO2 + NO is based on Paulot et al. (2009, ACP).ISOPO2 + HO2 is based on Paulot et al. (2009, Science).Isomerization of ISOPO2 is based onPeeters et al. (2009, PCCP) and Crounse et al. (2011, PCCP) .

NO

12

34

OH

11.7%

O

MVK

First generation isoprene nitrates

O

MACRH

O

H

HCHO

88%Organic peroxides

OH

OO

OO

OH

-hydroxyl peroxy radicaland isomers

-hydroxyl peroxy radicaland isomers

71% 29%

HO2 1,6-H shif t isomerization

4.7%

7.3%

12%26% 40% 66%

HOOO

HPALDs

hvOH100%

100%

C2 and C3 carbonyl compounds

ISOPO2 ISOPO2

This chemistry was implemented in GEOS-Chem

Ozone in the boundary layer during ICARTT 2004

Observations Model

Obs vs. Model

Improved O3-CO correlations due to:1. Recycling of NOx

from isoprene nitrates

2. HO2 uptake (lower OH and increase NOx lifetime).

(Mao et al., 2013, JGR)

Mean vertical profiles during ICARTT

O3 has no bias in boundary layer and free troposphere.HCHO provides good constraint on isoprene emissions.

ObservationsModel (GEOS-Chem)

(Mao et al., 2013, JGR)

Total alkyl nitrates (∑ANs) during ICARTT

Model well reproduced ∑ANs.

∑ ANs is dominated by secondary organic nitrates(C3-C4).

∑ANs vs. HCHO ∑ANs vs. O3

Model well reproduced ∑ANs vs. HCHO and ∑ANs vs. O3 correlations.

These correlations cannot be reproduced by a fast isomerization channel of RO2.

Vertical profiles Speciation of ∑ANs

(Mao et al., 2013, JGR)

NOy budget in eastern U.S. boundary layer for July 2004

Species Emission Chemical(P-L)

Dry Deposition

Wet Deposition

Net Export

NOx 386 -337 44 ------ 5

PANs   24 13 ------ 11

∑ANs          

ANs   18 7.4 3.6 7

R4N2   10 0.5 ------- 10

HNO3   277 180 110 -3

Export of ∑ANs > Export of PANs

(Mao et al., 2013, JGR)

New chemistry

Previous studies without NOx recycling

Current anthro NOx emissions (2004)

Reduce current anthro NOx emissions by 50%

Isoprene↑NOx ↓OH ↓O3 ↓ due to O3+ISOP

Surface ozone response to isoprene emissions

NOx emissions↓

Sensitivity of ozone to isoprene emissions ↓

(Mao et al., 2013, JGR)

Summary on ozone uncertainties

• Current best estimate of isoprene nitrate yield is 12%, with ~50% recycling efficiency of NOx.

• This results in a positive dependence of ozone on isoprene emissions throughout the U.S.

• Good agreement between observed and modeled total alkyl nitrates provides additional evidence on the isomerization rates.

Part 3: Uncertainties in nighttime chemistry

NO3

ONO2

OO

NO3

ONO2

O

ONO2

O

OH

O2NO

O

R4N2

Nighttime chemistry

Nighttime yield of organic nitrates is 70%>> daytime yield (11.7%)

(Horowitz et al., 2007, JGR) (Mao et al., 2013, JGR)

R4N2 is mainly produced at nightNO3 oxidation dominates organic nitrate production

All current models show that a large portion of daytime alkyl nitrates are from nighttime oxidation.

Sunrise

Entrainment zone

Boundary layer structure by Stull (1988).

How does nighttime chemistry affect global nitrogen/ozone budget?

Sunset

Part 4 : New effort on understanding BVOCs oxidation

Field studies over Southeast US in the summer of 2013SENEX (NOAA)

SOAS (NSF & EPA)NOMADSS (NCAR)

Two aircrafts based at Smyrna, TN and a tower located at Centerville, Alabama.

Measurements include VOC, NOx, ozone, aerosols, CCN etc.

GFDL provided C180 nudge simulations to SENEX data archive.

A modeling workshop to be held in GFDL this summer.

GFDL AM3 configuration for SENEX• Fully coupled chemistry-climate model

o Parameterizes aerosol activation into liquid cloud dropletso solves both tropospheric and stratospheric chemistry over the full domain

• Nudging wind with GFS meteorological field• High resolution (50 x 50 km) and coarse resolution (200 x 200 km)• MEGAN biogenic emissions (process-based emission)• Anthropogenic emissions use RCP 8.5 scenario (0.5 x 0.5 degree)• New isoprene chemistry (Mao et al., 2013 JGR)

C48 (200 x 200km) C180 (50 x 50km)

Monthly mean ozone for July of 2012

NOx emissions has been reduced by 34% from 2005 to 2011

OMI NO2 column in 2005 (summer)

OMI NO2 column in 2011 (summer)

difference

(Russell et al. 2012, ACP)

OH

Organic peroxy radicals

NOx

~10%

~90%

Alkyl nitrates

HCHO + MVK + MACR + other compounds

HO2

Organic peroxides

Terminal sink for radicals

Isoprene

RO2

ROOH

RONO2

OH

O OH

+ OH

HOOO

isomerization

OHphotolysis

HPALD

Epoxide

Based on our current understanding…

Can we see a shift from high NOx pathway to low NOx pathways?Would that mean we will have more SOA with the reduction of NOx?

SENEX (Southeast) flight track

Preliminary model results

Next step: Organic aerosols over Southeast US

fuel/industry open fires

OH, O3,NO3SOG SOA

POA

K

vegetation fuel/industry open fires

700

isopreneterpenesoxygenates…

30 alkenesaromaticsoxygenates…

VOC EMISSION PRIMARY EMISSION

VOC

50 20 100

20

Global sources in Tg C y-1

Two-product

SOA ≡ secondary organic aerosolPOA ≡ primary organic aerosol

Aqueous reactions

?

?

Uptake on aerosols

Temperature trend over past century1950-2006 for May-June (Unit: K/Decade)

(Leibensperger et al., 2012, ACP)

This temperature trend cannot be explained by the change in precipitation or dynamic patterns (El Niňo, NAO) (Portmann et al., 2009, PNAS).

1930-1990 change in Annual Mean Surface Temperature

Current hypothesis: this warming hole is, at least partially, due to the secondary organic aerosols over the eastern US (Goldstein et al., 2009, PNAS).

Thanks!

Model of Emission of Gases and Aerosols from Nature (MEGAN)Process-based emission inventory

ageLAIPART

Temperature dependence Light dependence

Leaf age

6

1iiiE

Emission factor

Fractional coverage

Leaf Area Index