CVAO

16° 52' N, 24° 52' W

Volatile organic compound observations

at the Cape Verde Atmospheric

Observatory (CVAO)

Lucy Carpenter, Katie Read, Shalini Punjabi, Ally Lewis, James Hopkins, James Lee, -

NCAS, University of York

Luis Mendes, Helder Lopez - INMG, Cape Verde

Steve Arnold - Earth and Environment, University of Leeds

Rachael Beale, Phil Nightingale – PML, UK

www.ncas.ac.uk/capeverdeobservatory/

Dispersion footprints of air arriving at Cape Verde

1) Atlantic and African coastal, 2) Atlantic marine,

3) North American and Atlantic 4) North American and coastal African,

5) European, 6) African, 7) European and African NAME model. Z. Fleming

Downwind of area of high biological productivity (Mauritanian upwelling)

0

0.1

0.2

0.3

0.4

0.5

0.6

Jul-0

6

Oct-0

6

Jan-0

7

Ap

r-07

Jul-0

7

Oct-0

7

Jan-0

8

May-0

8

Au

g-08

No

v-08

Feb-0

9

May-0

9

Au

g-09

No

v-09

Feb-1

0

Ch

l-a

(mg/

m3) MODIS

Measurement Method

Met stations at 10, 30m Various

O3 UV absorption

NO/NOx/NOy Chemiluminesence

CO VUV Fluorescence

C2-C8 NMHCs and DMS dc-GC-FID

C1-C5 O-VOC dc-GC-FID

Halocarbons GC-MS

JO1D Radiometer

VOC sampling

J.R Hopkins et al. J. Environ.Monit., 5 (1) , 8-13

Dual-bed

adsorbent trap

In-situ sampling

from 10-m tower

Condensation trap

10m LOWOX

column

50m PLOT

column

FID 2 FlD 1 Agilent

6890

Per Carbon Response factor (P.C.R.F)

Calibration: NMHCs

•Multi component VOC mixture NPL- 30 component mix (4 ppb range)

•Calibration frequency : every two-four weeks

Results of GAW audit for NMHCs

• RSD of CVAO NMHC cals < 2% for most compounds

R.f. of OVOC = conversion

factor x Response factor of

propane

Precision ~ 15%

Estimated accuracy ~ 20%

Calibration: OVOCs

0.000

0.005

0.010

0.015

0.020

0.025

are

a/p

pb

v/m

l a)

0.000

0.002

0.004

0.006

0.008

area

/ppb

v/m

l

b)

0.000

0.003

0.006

0.009

0.012

area

/ppb

v/m

l c)

Black squares = permeation

tubes (Kintek)

Grey squares = relative

response to propane based on

Apel-Reimer 14 component mix

standard analysed in York 2005

Error bars = average standard

deviation (1 ) of the perm tube

measurements

methanol

acetone

acetaldehyde

Integration – GC Werks

NMHC time series

First-look trends (Apr-May averages)

First-look trends (Apr-May averages)

CO flask data

from M.

Heimann,

Jena

Ethane

CH4 (Monthly mean - 5 year running mean)

Ethane and CH4 growth rate

CH

4 (

5 y

ea

r ru

nn

ing

me

an

)

Methane data

from M.

Heimann, Jena

• 1985-2010 saw global ethane decline of 190 pptv

(24%) (Simpson et al., Nature, 2012)

• Declining fugitive fossil fuel emissions

• At CVAO, [ethane] and CH4 growth rate fairly

stable over last 5 years

Biogenic VOCs: Isoprene

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0.1

0.2

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0.4

0.5

0.6

Aug

-06

Dec-06

Apr-07

Aug

-07

No

v-07

Mar-0

8

Jul-08

No

v-08

Mar-0

9

Jul-09

No

v-09

Mar-1

0

Jul-10

No

v-10

Ch

l-a

(mg/

m3 )

MODIS

0.00

5.00

10.00

15.00

20.00

25.00

30.00

35.00

40.00

Aug/06 Mar/07 Sep/07 Apr/08 Oct/08 May/09 Dec/09 Jun/10 Jan/11 Jul/11

Iso

pre

ne

/ p

ptv

hourly data

monthly average with std dev

Comparison of model with CVAO isoprene data

Arnold et al., ACP, 2009. Model runs for Cape Verde.

Observations generally fall between lower and upper estimates of marine isoprene emissions

0.001

0.01

0.1

1

10

100

DecJanFebMarAprMayJun Jul AugSepOctDec

iso

pre

ne

(pp

tv)

top down 1.7 Tg C/yr

bottom up 0.27 Tg C/yr

2008/2009/2010 CVAO data

Daytime maximum in atmospheric isoprene

Mean diurnal cycles in summertime (May-Oct only)

atmospheric isoprene at Cape Verde 2006-2010

0.00

1.00

2.00

3.00

4.00

5.00

6.00

0.00 6.00 12.00 18.00 24.00

Iso

pre

ne

/ p

ptv

UTC

0.0E+00

1.0E+09

2.0E+09

3.0E+09

00:00 06:00 12:00 18:00 00:00

iso

pre

ne

em

issi

on

s, m

ole

c cm

-2s-1

Predicted oceanic isoprene emissions

Liakakou et al. 2010 (eastern Med) : Inferred fluxes of 108 molec cm-2 s-1

(March) to 6 x109 molec cm-2 s-1 (June) from atmospheric meas

Gannt et al. 2009: Predicted fluxes from ~5 x105 to 6 x108 molec cm-2 s-1

Emissions calculated from

atmospheric isoprene

measurements and

calculated losses due to OH

and O3

(preliminary data)

•Over tropical waters, marine isoprene-derived SOA could contribute

over 40% of the total sub-micron OC fraction of marine aerosol, and

up to 100% (during midday hours) to sub-micron marine OC fluxes

Marine isoprene-derived SOA?

% contribution of 1 hr averaged daily maximum

isoprene-derived SOA to corresponding total sub-micron marine OC emissions for July --Gantt et al. ACP,

2009

Used 3% yield isoprene-SOA

Predicted

fluxes from ~5

x105 to 6 x108

molec cm-2 s-1

Oxygenated volatile organic compounds (OVOCs)

N

Methanol

Acetaldehyde

Acetone

Atmospheric OVOCs

Cape Verde Atmospheric

Observatory (CVAO)

Ocean: source or sink?

Biogenic

sources

Anthropogenic and

biomass burning sources

OH loss in marine

boundary layer

Primary and secondary sources

CH3C(O)O2

NO2 PAN

HO2 organic

acids

HCHO, HOx, CH3O2

h , O2, OH

h , O2, OH

Source of HOx, O3 and PAN

CAM-Chem vs measurements

acetone (ppt)

methanol (ppt)

acetaldehyde (ppt)

OVOC Water Measurements

-25

-20

-15

-10

-5

0

5

10

15

20

25

0 2 4 6 8

oN

oS

Acetaldehyde (nM)

Lati

tud

e

• Methanol,

acetaldehyde

and acetone

quantified in

seawater via

MI-PTR/MS

0

5

10

15

20

25

30

0 1 2 3 4 5 6 7

Acetaldehyde in Mauritanian Upwelling (ICON)

Filament 1

Filament 2 A

ceta

ldeh

yd

e (n

M)

Days since patch initiation (T0)

AMT track

Beale, R. Quantif ication of oxygenated volatile organic compounds (OVOCs) in

seawater, 2011, Ph.D thesis, University of East Anglia, UK. Manuscripts in preparation.

Role of the tropical Atlantic oceans?

CDOM

hv OVOC

•Jacob et al. (2002)- ocean a

significant source of acetone

Does inclusion of ocean sources/sinks improve model?

•Better agreement overall

•Missing acetone source in

autumn?

•Missing acetaldehyde all year

round

Biogenic contributions

Biomass

burning

Terrestrial

biosphere

Anthro-

pogenic

Observations

Standard model Ocean model

•Model may be missing

terrestrial biogenic OVOC

emissions

•Model scheme for OVOCs

Constrained by OVOC

observations No OVOCs Ocean model

Effect on [OH]

• Low model bias in [OVOC] may result in up to 25% missing model OH

reactivity

• Underestimation of [acetaldehyde] responsible for ~70% of OVOC

reduction of [OH

• If results representative of oceans, could result in up to 8%

underestimation of the global CH4 lifetime

Acknowledgements

Funding:

Bruno Faria, INMG

Martin Heimann and Lena

Kozlova for CH4 data