Science highlights from the Cape Verde Observatory (CVAO) Lee, J.D. a - - PowerPoint PPT Presentation

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Science highlights from the Cape Verde Observatory (CVAO) Lee, J.D. a - - PowerPoint PPT Presentation

Jul 07, 2023 228 likes •429 views

Science highlights from the Cape Verde Observatory (CVAO) Lee, J.D. a , Read, K.A. b , Carpenter, L.J. a , Lewis, A.C. a , Moller, S.J. a , Mendes, L.M. c , Fleming Z. d , Evans, M. J. e a National Centre for Atmospheric Science (NCAS), University

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SLIDE 1

Science highlights from the Cape Verde Observatory (CVAO)

Lee, J.D.a, Read, K.A.b , Carpenter, L.J.a, Lewis, A.C.a, Moller, S.J.a, Mendes, L.M.c, Fleming Z.d, Evans, M. J.e

a National Centre for Atmospheric Science (NCAS), University of York, UK bFacility for Ground based Atmospheric Measurements (FGAM), NCAS, University of York, UK cInstituto de Naçional de Meteorologia e Geofísica (INMG), Mindelo, Cape Verde d NCAS, University of Leicester, UK e University of Leeds, UK

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SLIDE 2

Cape Verde Observatory

Using Met office NAME model, Carpenter et al., 2011

5 10 15

30 60 90 120 150 180 210 240 270 300 330

5 10 15

wind speed / ms-1

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SLIDE 3

O3 < 340nm O1D H2O OH HO2

CO

H2O2 NO NO2 O3 CH3O2 CH3O Peroxides NO NO2 O3 O2 HCHO

CH4/ VOCs

CO2 HO2 HO2

Atmospheric photochemistry

Overview of Talk

  • Discussion of O3 measurements
  • Comparison to GEOSCHEM
  • Influence of radiation and NOx on O3 depletion
  • CO record
  • Comparison to GEOSCHEM
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SLIDE 4

Tropospheric ozone record

10 20 30 40 50 60 Aug/2006 Aug/2007 Aug/2008 Aug/2009 Aug/2010 O3 (ppbV) O3 (monthly ave) 20.0 25.0 30.0 35.0 40.0 45.0 00:00 04:48 09:36 14:24 19:12 00:00 O3 (ppbV) winter spring summer autumn

Diurnal cycle of O3 by season for 2007 (left) and 2010 (right).

20.0 25.0 30.0 35.0 40.0 45.0 00:00 04:48 09:36 14:24 19:12 00:00 O3 (ppbV) winter spring summer autumn

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SLIDE 5

Ozone diurnals and halogen influence

In 2008 we published a paper where we modelled the depletion and found that we had to invoke halogen chemistry to reproduce the measurements.

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2

Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep

delta O3 / ppb day-1

Read et al., Nature, 2008 ∆O3 – ppb O3 loss per day

Measured ∆O3 GEOSCHEM ∆O3 Box model ∆O3 without halogens (MCM 3.1) Box model ∆O3 with IO and BrO chemistry

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1 2 3 4 00 06 12 18 00

BrO / pptv

1 2 00 06 12 18 00

IO / pptv

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SLIDE 6

y = 0.2139x - 4.658 R2 = 0.368

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2 4 6 8 5 10 15 20 25 30 35 40 NO / pptv delta O3 / ppbv in 8 hours

Tropospheric O3 budget

  • Photolysis plays a significant role although balanced to some

extent by the entrainment term.

  • Competition between photochemical loss and production of

O3 through: -

NO2 + hν (+O2) → NO + O3 NO + HO2 → OH + NO2 OH + RO (+O2) → HO2 + RO2

….leads to a nonlinear dependency of O3 on NOx.

  • Lee et al. looked at this relationship and found that in this

region there is a level of NOx at which there is a switch from net destruction to production of O3, the “O3 compensation point” (Lee et al., J. Geophys. Res., 2009).

  • In the MBL bromine and iodine atoms have been shown

to be important in the role of O3 destruction in this region (Read et al., Nature, 2008).

X + O3 → XO + O2 XO + XO → 2X + O2 XO + IO → X + OIO XO + HO2 → HOX + O2 HOX + hu → OH + X XO + NO → NO2 + X

  • XO causes a decrease in the NO/NO2 ratio but O3 is not

increased because the X formed will likely destroy O3.

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SLIDE 7

Delta O3 , the role of photolysis and air mass history

  • Better agreement when

sampling Atlantic conditions than coastal African conditions.

  • The modelled and

measured follow the same trend most of the time in-line with the dominance of the O3 photolysis term.

10 20 30 40 50 60 70 80 90 100 Mar/08 Apr/08 May/08 Jun/08 Jul/08 Aug/08 Sep/08 Oct/08 Nov/08 % contribution of each sector

African (dust) Polluted Coastal African Atlantic Continental Atlantic Marine

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2 Oct/06 Apr/07 Nov/07 May/08 Dec/08 Jul/09 Jan/10 Delta O3 / ppbv 100 200 300 400 500 600 700 800 900 1000

measured monthly average GEOSCHEM monthly average Slr_W_Avg

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2 Oct/06 Apr/07 Nov/07 May/08 Dec/08 Jul/09 Jan/10 Delta O3 / ppbv 100 200 300 400 500 600 700 800 900 1000

measured monthly average GEOSCHEM monthly average Slr_W_Avg

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SLIDE 8

GEOS CHEM comparisons O3

10 20 30 40 50 60 Oct/06 Feb/07 Jul/07 Dec/07 May/08 Oct/08 Mar/09 Aug/09 Jan/10 O3 (ppbV) GEOSCHEM O3 CVAO O3

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SLIDE 9

NOx

5 10 15 20 25 30 Oct-06 Apr-07 Oct-07 Apr-08 Oct-08 Apr-09 Oct-09 NO / pptv NO measured NO GEOS

25 50 75 100 NO2 / pptv NO2 measured NO2 GEOS

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SLIDE 10

Delta O3 and NO/NO2 ratio

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2 Oct/06 Apr/07 Nov/07 May/08 Dec/08 Jul/09 Jan/10 Delta O3 / ppbv

  • 2.25
  • 1.75
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0.25 0.75 measured monthly average GEOSCHEM monthly average measured NO/NO2 ratio GEOSCHEM NO/NO2 ratio

y = 0.2139x - 4.658 R2 = 0.368 y = 0.3531x - 2.8144 R2 = 0.3537

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2 4 6 8 5 10 15 20 25 30 35 40 NO / pptv delta O3 / ppbv in 8 hours

  • The modelled NO/NO2 ratio is

generally too high although agrees better in 2009.

  • However NO2 (and often NO-

see plot below) are also much higher in the measurements compared to the model (sometimes by 5x).

  • NO correlates with delta O3 in

the measurements and model

  • Not enough XO to explain the

difference in modelled to measured NO / NO2 ratio

  • Other processes going on
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SLIDE 11

GEOS / meas comparisons NOy

NOy = Sum NOx, NO3, HNO3, N2O5, PANs, HONO, alkyl nitrates and particulate nitrate.

10 20 30 40 50 60 70 80 90 100 Oct/06 Mar/07 Aug/07 Jan/08 Jun/08 Nov/08 Apr/09 Sep/09 % contribution of each sector

African (dust) Polluted Coastal African Atlantic Continental Atlantic Marine

100 200 300 400 500 600 700 800 900 1000 NOy / pptv NOy meas NOy GEOS

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SLIDE 12

25 50 75 100 125 150 175 200 Sep-06 Feb-07 Jul-07 Dec-07 May-08 Oct-08 Mar-09 Aug-09 Dec-09 May-10 Oct-10 CO / ppbv

CO meas CO GEOS CO (ppb)

CO and ethane comparison to GEOS CHEM

Is the amplitude of the CO correct for the wrong reasons? Can the emissions be underestimated all year? If we increase the Spring emissions to similar to those needed for ethane then the amplitude is too large, need additional sources in summer.

500 1000 1500 2000 2500 Sep/06 Feb/07 Jul/07 Dec/07 May/0 Oct/08 Mar/0 Aug/09 Jan/10 Jun/10 Oct/10 ethane (pptv) 500 1000 1500 2000 2500 Sep/06 Feb/07 Jul/07 Dec/07 May/08 Oct/08 Mar/09 Aug/09 Jan/10 Jun/10 Oct/10 ethane (pptv) ethane measured GEOS ethane

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SLIDE 13

Other sites CO with GFDL GCTM model

Purple measured Black-modelled Red-Fossil fuel Blue- Biogenic hydrocarbon Green-Biomass Orange - Methane oxidation

Holloway et al., 2000

The relative contributions show that fossil fuel emissions dominate in late winter/early spring but other sources compete in summer. No seasonal distribution assumed in fossil fuel emissions so changes arise from changes in transport and OH conc. Methane oxidation is similar all year. We fall between Tenerife and Ascension, you can see the difference in the contributions between the two sites…… Biogenic hydrocarbon influence in summer….

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SLIDE 14
  • CO and ethane share some common

sources e.g. fossil fuel emissions, and biomass burning. The ratio of CO : ethane emissions from these sources is not thought to vary seasonally.

  • “n[OH]” can be calculated from ethane

and applied to calculate a theoretical CO assuming no other sources exist and all loss routes are also shared.

  • If the modelled CO amplitude is correct

then is there a year-round underestimate

  • f emissions?

50 100 150 200

Oct/06 Dec/06 Jan/07 Mar/07 May/07 Jul/07 Sep/07 Nov/07 Jan/08 Mar/08

CO (ppbV) 500 1000 1500 2000 2500 3000 3500 ethane (pptV) OH dependent fit to CO Sinusoidal fit to ethane OH dependent fit to ethane

Read et al., J. Geophys. Res., 2009

Using ethane to interpret CO

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SLIDE 15

Seasonal distribution

  • Methanol shows variability with air

mass trajectory.

  • Higher levels during Spring (Mar-

Apr) in-line with the precursor NMHC and their shared sources (later for methanol than acetone). OH is also lowest at this time.

  • June-radiation decreases.
  • (Elevated levels are also observed in

Aug-September correlating with maximum in air temperature (increased biogenic sources, photochemical influence on secondary chemistry).

  • Source of CO from NMVOC is a

cause of high uncertainty (>factor of 3) in models (Holloway et al., 2000) Potentially up to 60% of the observed summer CO is from summertime increases in the seasonal trend of NMVOC (and methane) oxidation.

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500 1000 1500 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec acetone and propane (pptV) 20 25 30 35 40 Air temperature (°C)

'NCA COASTAL NAA AM AFR propane 24 per. Mov. Avg. (AirTC_Avg)

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500 1000 1500 2000 2500 3000 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec methanol (pptV) 1800 1820 1840 1860 1880 1900 1920 1940 1960 1980 methane (ppbV)

NCA COASTAL NAA AM AFR methane

Read et al., J. Geophys. Res., 2009

y = 13.32x + 461.80 R2 = 0.53 y = 7.36x + 628.90 R2 = 0.83 y = 13.52x + 622.33 R2 = 0.64

500 1000 1500 2000 2500

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20 40 60 80 100 CO measurements - CO fit (ppbv)

  • voc (pptv)

acetone acetaldehyde methanol

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SLIDE 16

Summary

  • The O3 depletion measurements have inspired much interest in the

Observatory.

  • Poorer model/measured delta O3 agreement when NO and ratio of NO/NO2 is
  • low. Is the difference in measured O3 depletion between 2007 and 2008 (with

changing NO) simply due to measurement variability of budget terms? What is the impact of halogens?

  • Better agreement with the global model when the NO is higher, and the ratio
  • f NO/NO2 is higher but the concentrations of NO and NO2 are

underestimated.

  • The distribution of NOx is well simulated in Atlantic marine conditions but not

when considering data from the continents. More NOx source information is needed to be addressed through NOy measurements.

  • CO shows fairly poor agreement to the global model.
  • Additional emissions in spring would lead to overestimation of concentrations

in summer.

  • VOC (acetone and methanol) peak in summer and through secondary

production could explain CO concentrations at this time.

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SLIDE 17

Acknowledgements

Atmospheric Group at York (Lucy Carpenter, Ally Lewis, Sarah Moller and others) Site Manager Luis Neves and Site Technician Helder Lopes Jens Tschitter for BrO and IO data Elena Koslova, Martin Heimann for CO data Zöe Fleming for NAME analyses SOLAS, TENATSO and now the National Centre for Atmospheric Science (NCAS) through FGAM for funding

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SLIDE 18

150oC Quartz

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Molybdenum converter 350oC Quartz

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600oC Quartz

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ΣPans  NO2 Sample in Aerosol >2µm removed by filter To Chemiluminescence NO analyser Photolytic converter NO2  NO ΣPans +ΣAlk Nit  NO2 ΣPans +ΣAlk Nit +HNO3  NO2 ‘All’ NOy  NO

  • NOx-main sources urban,

industrial areas

  • Oxidation to HNO3, PAN,

alkylnitrates <1 day.

  • Diurnal cycles in NOx may

indicate production from PAN, HNO3, HONO

NOy speciation